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<document id="9AE42FA18F7CEDA356160FAB09FFB09A" ID-CLB-Dataset="23013" ID-DOI="10.1126/sciadv.aax6250" ID-GBIF-Dataset="60d937e4-d9be-45e7-a532-afd33e2c5283" ID-PMC="PMC6938697" ID-PubMed="31911944" ID-Zenodo-Dep="3749024" IM.bibliography_approvedBy="felipe" IM.metadata_approvedBy="admin" IM.taxonomicNames_approvedBy="admin" IM.treatments_approvedBy="admin" checkinTime="1586697798913" checkinUser="jeremy" docAuthor="Holly N. Woodward, Katie Tremaine, Scott A. Williams, Lindsay E. Zanno, John R. Horner &amp; Nathan Myhrvold" docDate="2020" docId="03E8486CFFE30E52FFBE5400FBC3FE74" docLanguage="en" docName="Woodwardetal2020.pdf" docOrigin="Science Advances (eaax 6250) 6" docStyle="DocumentStyle{}" docTitle="Tyrannosaurus rex Osborn 1905" docType="treatment" docVersion="14" lastPageNumber="7" masterDocId="FFD13014FFE30E54FFDE5763FF88FF89" masterDocTitle="Growing up Tyrannosaurus rex: Osteohistology refutes the pygmy “ Nanotyrannus ” and supports ontogenetic niche partitioning in juvenile Tyrannosaurus" masterLastPageNumber="8" masterPageNumber="1" pageNumber="1" updateTime="1727402517684" updateUser="ExternalLinkService">
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<mods:title id="F132D6AEFB8A9AE0339236ACC5335A77">Growing up Tyrannosaurus rex: Osteohistology refutes the pygmy “ Nanotyrannus ” and supports ontogenetic niche partitioning in juvenile Tyrannosaurus</mods:title>
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<mods:namePart id="0553F979604B8A4553C6CF41CF4A3053">Holly N. Woodward</mods:namePart>
<mods:affiliation id="80FFE6EF49B1F74E3066938201F3143A">Department of Anatomy and Cell Biology, Oklahoma State University Center for Health Sciences, 1111 W. 17 th St., Tulsa, OK 74104, USA</mods:affiliation>
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<mods:namePart id="4226D3A6F939FBC341D6C373309FDE6E">Katie Tremaine</mods:namePart>
<mods:affiliation id="97ECD2340CF329D57332FD952FCB08EC">Department of Earth Science, Montana State University, P. O. Box 173480, Bozeman, MT 59717, USA. Museum of the Rockies, Montana State University, 600 W. Kagy Blvd., Bozeman, MT 59717, USA</mods:affiliation>
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<mods:namePart id="DE5AB0F549E0CCBE42485194082A3154">Scott A. Williams</mods:namePart>
<mods:affiliation id="E50151B185F60029B50950016B0F98AD">Museum of the Rockies, Montana State University, 600 W. Kagy Blvd., Bozeman, MT 59717, USA</mods:affiliation>
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<mods:namePart id="77A8AAA14334140E0023B8B04AA0BE04">Lindsay E. Zanno</mods:namePart>
<mods:affiliation id="2EC71DE62DCA2A3539CA5256E4D4A36A">Paleontology, North Carolina Museum of Natural Sciences, 11 W. Jones St., Raleigh, NC 27601, USA. Department of Biological Sciences, North Carolina State University, 3510 Thomas Hall, Campus Box 7614, Raleigh, NC 2769, USA</mods:affiliation>
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<mods:namePart id="B1C176E1EC5FDD43EA5055C9285B53BE">John R. Horner</mods:namePart>
<mods:affiliation id="AC3B93F2E866C43F9C5BA5575F4EC30E">Chapman University, 1 University Dr., Orange, CA 92866, USA</mods:affiliation>
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<mods:namePart id="FF87E6C5E8CF73E2DD4AD9373C046A8F">Nathan Myhrvold</mods:namePart>
<mods:affiliation id="B755FB9F1C55A37DC8531FDC3AF99AEA">Intellectual Ventures, 3150 139 th Avenue Southeast, Bellevue, WA 98005, USA.</mods:affiliation>
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<treatment id="03E8486CFFE30E52FFBE5400FBC3FE74" ID-DOI="http://doi.org/10.5281/zenodo.3808815" ID-GBIF-Taxon="190305446" ID-Zenodo-Dep="3808815" LSID="urn:lsid:plazi:treatment:03E8486CFFE30E52FFBE5400FBC3FE74" httpUri="http://treatment.plazi.org/id/03E8486CFFE30E52FFBE5400FBC3FE74" lastPageId="6" lastPageNumber="7" pageId="0" pageNumber="1">
<subSubSection id="C35BAAF1FFE30E54FFBE5400FEF4FC5A" pageId="0" pageNumber="1" type="nomenclature">
<paragraph id="8BFEF97AFFE30E54FFBE5400FEF4FC5A" blockId="0.[96,776,837,1595]" pageId="0" pageNumber="1">
After the publication of its discovery from the famous Hell Creek Formation (HCF) in 1905, the carnivorous dinosaur
<taxonomicName id="4C4182F9FFE30E54FD8A54E2FC80FC11" authorityName="Osborn" authorityYear="1905" box="[596,776,897,920]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="1" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE30E54FD8A54E2FC80FC11" box="[596,776,897,920]" italics="true" pageId="0" pageNumber="1">Tyrannosaurus rex</emphasis>
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(
<bibRefCitation id="EFD0848BFFE30E54FFB654FEFFFCFC3C" author="H. F. Osborn" box="[104,116,925,949]" journalOrPublisher="Bull. Am. Mus. Nat. Hist." pageId="0" pageNumber="1" pagination="259 - 265" part="21" refId="ref7084" refString="1. H. F. Osborn, Tyrannosaurus and other Cretaceous carnivorous dinosaurs. Bull. Am. Mus. Nat. Hist. 21, 259 - 265 (1905)." title="Tyrannosaurus and other Cretaceous carnivorous dinosaurs" type="journal article" year="1905">
<emphasis id="B9352568FFE30E54FFB654FEFFFCFC3C" box="[104,116,925,949]" italics="true" pageId="0" pageNumber="1">1</emphasis>
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) was met with intense scientific interest and public popularity, which persists to the present day (
<bibRefCitation id="EFD0848BFFE30E54FEBD54D8FEE7FC5A" author="S. L. Brusatte &amp; M. A. Norell &amp; T. D. Carr &amp; G. M. Erickson &amp; J. R. Hutchinson &amp; A. M. Balanoff &amp; G. S. Bever &amp; J. N. Choiniere &amp; P. J. Makovicky &amp; X. Xu" box="[355,367,955,979]" journalOrPublisher="science" pageId="0" pageNumber="1" pagination="1481 - 1485" part="329" refId="ref7118" refString="2. S. L. Brusatte, M. A. Norell, T. D. Carr, G. M. Erickson, J. R. Hutchinson, A. M. Balanoff, G. S. Bever, J. N. Choiniere, P. J. Makovicky, X. Xu, Tyrannosaur paleobiology: New research on ancient exemplar organisms. science 329, 1481 - 1485 (2010)." title="Tyrannosaur paleobiology: New research on ancient exemplar organisms" type="journal article" year="2010">
<emphasis id="B9352568FFE30E54FEBD54D8FEE7FC5A" box="[355,367,955,979]" italics="true" pageId="0" pageNumber="1">2</emphasis>
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).
</paragraph>
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<paragraph id="8BFEF97AFFE30E54FE5E54D8FDC9FA6A" blockId="0.[96,776,837,1595]" pageId="0" pageNumber="1">
Numerous hypotheses concerning
<taxonomicName id="4C4182F9FFE30E54FD0F54D8FC80FC5B" authorityName="Osborn" authorityYear="1905" box="[721,776,955,978]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="1" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE30E54FD0F54D8FC80FC5B" box="[721,776,955,978]" italics="true" pageId="0" pageNumber="1">T. rex</emphasis>
</taxonomicName>
biology and behavior result from decades of research primarily focused on skeletal morphology and biomechanics [e.g., (
<bibRefCitation id="EFD0848BFFE30E54FD545496FD1EFB84" author="P. L. Larson &amp; K. Carpenter" box="[650,662,1013,1037]" journalOrPublisher="Indiana Univ. Press, Bloomington" pageId="0" pageNumber="1" refId="ref7198" refString="3. P. L. Larson, K. Carpenter, Tyrannosaurus Rex, the Tyrant King. (Indiana Univ. Press, Bloomington, 2008)." title="Tyrannosaurus Rex, the Tyrant King" type="book" year="2008">
<emphasis id="B9352568FFE30E54FD545496FD1EFB84" box="[650,662,1013,1037]" italics="true" pageId="0" pageNumber="1">3</emphasis>
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) and references therein]. Only within the past 15 years has bone histology been applied to investigate the aspects of
<taxonomicName id="4C4182F9FFE30E54FE075352FD9EFBC1" authorityName="Osborn" authorityYear="1905" box="[473,534,1073,1096]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="1" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE30E54FE075352FD9EFBC1" box="[473,534,1073,1096]" italics="true" pageId="0" pageNumber="1">T. rex</emphasis>
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life history inaccessible from gross examinations, addressing questions concerning ontogenetic age, growth rate, skeletal maturity, and sexual maturity. In 2004, two teams independently assessed the growth dynamics of
<taxonomicName id="4C4182F9FFE30E54FD5153EAFD42FB29" authorityName="Osborn" authorityYear="1905" box="[655,714,1161,1184]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="1" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE30E54FD5153EAFD42FB29" box="[655,714,1161,1184]" italics="true" pageId="0" pageNumber="1">T. rex</emphasis>
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using osteohistology. Their results suggest that
<taxonomicName id="4C4182F9FFE30E54FDD853C5FDC8FB34" authorityName="Osborn" authorityYear="1905" box="[518,576,1190,1213]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="1" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE30E54FDD853C5FDC8FB34" box="[518,576,1190,1213]" italics="true" pageId="0" pageNumber="1">T. rex</emphasis>
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had an accelerated growth rate compared with other tyrannosaurids and achieved adult size in approximately two decades (
<bibRefCitation id="EFD0848BFFE30E54FE685383FE4AFB71" author="G. M. Erickson &amp; P. J. Makovicky &amp; P. J. Currie &amp; M. A. Norell &amp; S. A. Yerby &amp; C. A. Brochu" box="[438,450,1248,1272]" journalOrPublisher="Nature" pageId="0" pageNumber="1" pagination="772 - 775" part="430" refId="ref7228" refString="4. G. M. Erickson, P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, C. A. Brochu, Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature 430, 772 - 775 (2004)." title="Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs" type="journal article" year="2004">
<emphasis id="B9352568FFE30E54FE685383FE4AFB71" box="[438,450,1248,1272]" italics="true" pageId="0" pageNumber="1">4</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE30E54FE125383FE50FB7E" author="J. R. Horner &amp; K. Padian" box="[460,472,1248,1271]" journalOrPublisher="Proc. R. soc. Lond. B Biol. sci." pageId="0" pageNumber="1" pagination="1875 - 1880" part="271" refId="ref7285" refString="5. J. R. Horner, K. Padian, Age and growth dynamics of Tyrannosaurus rex. Proc. R. soc. Lond. B Biol. sci. 271, 1875 - 1880 (2004)." title="Age and growth dynamics of Tyrannosaurus rex" type="journal article" year="2004">
<emphasis id="B9352568FFE30E54FE125383FE50FB7E" box="[460,472,1248,1271]" italics="true" pageId="0" pageNumber="1">5</emphasis>
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). The teams focused on growth curves, rather than on detailed analyses or interpretations of bone tissue microstructures. However, osteohistology is critical for establishing a baseline against which skeletal maturity and growth changes in cortical morphology related to life events in this taxon can be tested. Identifying the timing of growth acceleration and empirically quantifying juvenile
<taxonomicName id="4C4182F9FFE30E54FEE952F2FEFBFA21" authorityName="Osborn" authorityYear="1905" box="[311,371,1425,1448]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="1" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE30E54FEE952F2FEFBFA21" box="[311,371,1425,1448]" italics="true" pageId="0" pageNumber="1">T. rex</emphasis>
</taxonomicName>
growth rates are of special importance because the juvenile growth record is lost in older individuals because of bone remodeling and resorption (
<bibRefCitation id="EFD0848BFFE30E54FDD152A8FD93FA6A" author="G. M. Erickson &amp; P. J. Makovicky &amp; P. J. Currie &amp; M. A. Norell &amp; S. A. Yerby &amp; C. A. Brochu" box="[527,539,1483,1507]" journalOrPublisher="Nature" pageId="0" pageNumber="1" pagination="772 - 775" part="430" refId="ref7228" refString="4. G. M. Erickson, P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, C. A. Brochu, Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature 430, 772 - 775 (2004)." title="Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs" type="journal article" year="2004">
<emphasis id="B9352568FFE30E54FDD152A8FD93FA6A" box="[527,539,1483,1507]" italics="true" pageId="0" pageNumber="1">4</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE30E54FDF952A8FDBBFA6B" author="J. R. Horner &amp; K. Padian" box="[551,563,1483,1506]" journalOrPublisher="Proc. R. soc. Lond. B Biol. sci." pageId="0" pageNumber="1" pagination="1875 - 1880" part="271" refId="ref7285" refString="5. J. R. Horner, K. Padian, Age and growth dynamics of Tyrannosaurus rex. Proc. R. soc. Lond. B Biol. sci. 271, 1875 - 1880 (2004)." title="Age and growth dynamics of Tyrannosaurus rex" type="journal article" year="2004">
<emphasis id="B9352568FFE30E54FDF952A8FDBBFA6B" box="[551,563,1483,1506]" italics="true" pageId="0" pageNumber="1">5</emphasis>
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).
</paragraph>
</subSubSection>
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Here, we examine the femur and tibia bone microstructure of two tyrannosaur skeletons of controversial taxonomic status recovered from the HCF: BMRP (Burpee Museum of Natural History) 2002.4.1, a largely complete specimen composed of nearly the entire skull and substantial postcranial material, and
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, a more fragmentary specimen. Respectively, we estimate these specimens to be 54 and 59% the body length of
<materialsCitation id="3B29F327FFE30E54FBB154FDFBBAFC5A" ID-GBIF-Occurrence="3396425373" collectionCode="FMNH" pageId="0" pageNumber="1" specimenCode="FMNH PR2081">FMNH (Field Museum of Natural History) PR 2081 (“Sue”)</materialsCitation>
(
<bibRefCitation id="EFD0848BFFE30E54FB9D54D8FBC7FC5A" author="J. R. Hutchinson &amp; K. T. Bates &amp; J. Molnar &amp; V. Allen &amp; P. J. Makovicky" box="[1091,1103,955,979]" journalOrPublisher="PLOs ONE" pageId="0" pageNumber="1" pagination="e 26037" part="6" refId="ref7327" refString="6. J. R. Hutchinson, K. T. Bates, J. Molnar, V. Allen, P. J. Makovicky, A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth. PLOs ONE 6, e 26037 (2011)." title="A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth" type="journal article" year="2011">
<emphasis id="B9352568FFE30E54FB9D54D8FBC7FC5A" box="[1091,1103,955,979]" italics="true" pageId="0" pageNumber="1">6</emphasis>
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,
<bibRefCitation id="EFD0848BFFE30E54FB8354D8FBE1FC5B" author="P. J. Currie" box="[1117,1129,955,978]" journalOrPublisher="Can. J. Earth sci." pageId="0" pageNumber="1" pagination="651 - 665" part="40" refId="ref7386" refString="7. P. J. Currie, Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia. Can. J. Earth sci. 40, 651 - 665 (2003)." title="Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia" type="journal article" year="2003">
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), one of the largest known
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<emphasis id="B9352568FFE30E54FA5354D8FA42FC5B" box="[1421,1482,955,978]" italics="true" pageId="0" pageNumber="1">T. rex</emphasis>
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. The ontogenetic age of
<materialsCitation id="3B29F327FFE30E54FBC654BAFB3FFC79" ID-GBIF-Occurrence="3396425367" box="[1048,1207,984,1008]" collectionCode="BMRP" pageId="0" pageNumber="1" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
was previously reported by Erickson (
<bibRefCitation id="EFD0848BFFE30E54FC505496FC12FB84" author="G. M. Erickson" box="[910,922,1013,1037]" journalOrPublisher="Trends Ecol. Evol." pageId="0" pageNumber="1" pagination="677 - 684" part="20" refId="ref7429" refString="8. G. M. Erickson, Assessing dinosaur growth patterns: A microscopic revolution. Trends Ecol. Evol. 20, 677 - 684 (2005)." title="Assessing dinosaur growth patterns: A microscopic revolution" type="journal article" year="2005">
<emphasis id="B9352568FFE30E54FC505496FC12FB84" box="[910,922,1013,1037]" italics="true" pageId="0" pageNumber="1">8</emphasis>
</bibRefCitation>
) as 11 years based on fibula osteohistology. However, because the fibula grows more slowly than the weight-bearing femur and tibia, it does not reflect annual increases in body size or relative skeletal maturity as accurately [e.g., (
<bibRefCitation id="EFD0848BFFE30E54FB4C532EFB16FBEC" author="H. N. Woodward &amp; J. R. Horner &amp; J. O. Farlow" box="[1170,1182,1101,1125]" journalOrPublisher="PeerJ" pageId="0" pageNumber="1" pagination="e 422" part="2" refId="ref7460" refString="9. H. N. Woodward, J. R. Horner, J. O. Farlow, Quantification of intraskeletal histovariability in Alligator mississippiensis and implications for vertebrate osteohistology. PeerJ 2, e 422 (2014)." title="Quantification of intraskeletal histovariability in Alligator mississippiensis and implications for vertebrate osteohistology" type="journal article" year="2014">
<emphasis id="B9352568FFE30E54FB4C532EFB16FBEC" box="[1170,1182,1101,1125]" italics="true" pageId="0" pageNumber="1">9</emphasis>
</bibRefCitation>
)]. We use femur and tibia data to (i) provide detailed comparative intra- and interskeletal histological descriptions, (ii) quantify the ontogenetic age and relative skeletal maturity of these specimens, and (iii) allow empirical observation of annual growth rate, with emphasis on variability during the life history of tyrannosaurs (
<bibRefCitation id="EFD0848BFFE30E54FBDB5383FB95FB71" author="K. Padian &amp; E. - T. Lamm" box="[1029,1053,1248,1272]" journalOrPublisher="University of California Press, Berkeley" pageId="0" pageNumber="1" pagination="285" refId="ref7502" refString="10. K. Padian, E. - T. Lamm, Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation (University of California Press, Berkeley, 2013), p. 285." title="Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation" type="book chapter" year="2013">
<emphasis id="B9352568FFE30E54FBDB5383FB95FB71" box="[1029,1053,1248,1272]" italics="true" pageId="0" pageNumber="1">10</emphasis>
</bibRefCitation>
).
</paragraph>
<paragraph id="8BFEF97AFFE30E54FC96539DFB01FA4F" blockId="0.[808,1488,837,1478]" pageId="0" pageNumber="1">
Moreover, by histologically quantifying the ontogenetic age of
<materialsCitation id="3B29F327FFE30E54FCF65278FC4DFABA" ID-GBIF-Occurrence="3396425352" box="[808,965,1307,1331]" collectionCode="BMRP" pageId="0" pageNumber="1" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
<materialsCitation id="3B29F327FFE30E54FC2B5278FB1AFABA" ID-GBIF-Occurrence="3396425332" box="[1013,1170,1307,1331]" collectionCode="BMRP" pageId="0" pageNumber="1" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
and inferring skeletal maturity, we present new data that can be used to evaluate competing taxonomic hypotheses regarding these and other mid-sized tyrannosaur specimens discovered in the HCF, specifically whether
<materialsCitation id="3B29F327FFE30E54FAE75210FA58FA02" ID-GBIF-Occurrence="3396425309" box="[1337,1488,1395,1419]" collectionCode="BMRP" pageId="0" pageNumber="1" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
(and by proxy other specimens) represents an adult “pygmy” genus of tyrannosaurid, “
<taxonomicName id="4C4182F9FFE30E54FC3652CDFBF1FA4C" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[1000,1145,1454,1477]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="1" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE30E54FC3652CDFBF1FA4C" box="[1000,1145,1454,1477]" italics="true" pageId="0" pageNumber="1">Nanotyrannus</emphasis>
</taxonomicName>
.”
</paragraph>
</subSubSection>
<subSubSection id="C35BAAF1FFE30E56FCF65166FB64F989" lastPageId="2" lastPageNumber="3" pageId="0" pageNumber="1" type="description">
<paragraph id="8BFEF97AFFE30E54FCF65166FC0FF995" blockId="0.[808,1488,1541,1888]" box="[808,903,1541,1564]" pageId="0" pageNumber="1">
<heading id="D0B64E16FFE30E54FCF65166FC0FF995" allCaps="true" bold="true" box="[808,903,1541,1564]" fontSize="9" level="2" pageId="0" pageNumber="1" reason="6">
<emphasis id="B9352568FFE30E54FCF65166FC0FF995" bold="true" box="[808,903,1541,1564]" pageId="0" pageNumber="1">RESULTS</emphasis>
</heading>
</paragraph>
<paragraph id="8BFEF97AFFE30E54FCF65140FA0CF8E9" blockId="0.[808,1488,1541,1888]" pageId="0" pageNumber="1">
For detailed, orientation-specific histology descriptions, refer to the Supplementary Materials. In general, the femur and tibia cortical bones of
<materialsCitation id="3B29F327FFE30E54FC9C513DFC57F9FC" ID-GBIF-Occurrence="3396425423" box="[834,991,1629,1653]" collectionCode="BMRP" pageId="0" pageNumber="1" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
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can be classified as a wovenparallel complex. Vascularity and osteocyte lacuna density are uniformly high throughout (
<figureCitation id="137AE5FFFFE30E54FBF751FBFBE4F939" box="[1065,1132,1688,1712]" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="0" pageNumber="1">Figs. 1</figureCitation>
and
<figureCitation id="137AE5FFFFE30E54FB4151FBFB26F939" box="[1183,1198,1688,1712]" captionStart="Fig" captionStartId="2.[96,126,773,793]" captionTargetBox="[313,1271,161,757]" captionTargetId="figure@2.[312,1272,160,758]" captionTargetPageId="2" captionText="Fig. 2. Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canalsι the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories." figureDoi="http://doi.org/10.5281/zenodo.3749028" httpUri="https://zenodo.org/record/3749028/files/figure.png" pageId="0" pageNumber="1">2</figureCitation>
). In the femora, the primary and secondary osteons surrounding vascular canals are frequently isotropic in the transverse section (
<figureCitation id="137AE5FFFFE30E54FB5551B0FAABF962" box="[1163,1315,1747,1771]" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="0" pageNumber="1">Fig. 1, A and B</figureCitation>
) and anisotropic in the longitudinal section (
<figureCitation id="137AE5FFFFE30E54FB9F5193FB05F881" box="[1089,1165,1776,1800]" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="0" pageNumber="1">Fig. 1C</figureCitation>
). Also in the transverse section, femur primary tissue exhibits moderate anisotropy regionally and weak anisotropy locally, corresponding to a loose arrangement of mineralized fibers in parallel (e.g.,
<figureCitation id="137AE5FFFFE30E54FB85502BFB7BF8D6" box="[1115,1267,1864,1888]" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="0" pageNumber="1">Fig. 1, A and B</figureCitation>
, and
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).
</paragraph>
<footnote id="E85AE574FFE30E54FFBE5106FF30F8D6" pageId="0" pageNumber="1">
<paragraph id="8BFEF97AFFE30E54FFBE5106FDB0F8BB" blockId="0.[96,778,1637,1887]" pageId="0" pageNumber="1">
<superScript id="7C345432FFE30E54FFBE5106FFEFF9FB" attach="right" box="[96,103,1637,1650]" fontSize="5" pageId="0" pageNumber="1">1</superScript>
Department of Anatomy and Cell Biology, Oklahoma State University Center for Health Sciences, 1111 W.17th St., Tulsa, OK 74104, USA.
<superScript id="7C345432FFE30E54FDC65118FD97F901" attach="right" box="[536,543,1659,1672]" fontSize="5" pageId="0" pageNumber="1">2</superScript>
Department of Earth Science, Montana State University, P.O. Box 173480, Bozeman, MT 59717, USA.
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Museum of the Rockies, Montana State University, 600 W.Kagy Blvd., Bozeman, MT 59717, USA.
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Paleontology, North Carolina Museum of Natural Sciences, 11 W. Jones St., Raleigh, NC 27601, USA.
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Department of Biological Sciences, North Carolina State University, 3510 Thomas Hall, Campus Box 7614, Raleigh, NC 2769, USA.
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<docAuthorAffiliation id="935E3619FFE30E54FFB95064FDD9F892" box="[103,593,1799,1819]" pageId="0" pageNumber="1">Chapman University, 1 University Dr., Orange, CA 92866, USA</docAuthorAffiliation>
.
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Intellectual Ventures, 3150 139th Avenue Southeast, Bellevue, WA 98005, USA.
</paragraph>
<paragraph id="8BFEF97AFFE30E54FFBE5057FF30F8D6" blockId="0.[96,778,1637,1887]" pageId="0" pageNumber="1">*Corresponding author. Email: holly.ballard@okstate.edu, holly.n.woodward@ gmail.com</paragraph>
</footnote>
<caption id="DF3EA9F2FFE20E55FFBE5327FE4EFAF6" ID-DOI="http://doi.org/10.5281/zenodo.3749026" ID-Zenodo-Dep="3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="1" pageNumber="2" startId="1.[96,125,1092,1112]" targetBox="[313,1271,161,1076]" targetPageId="1">
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Fig. 1. Femur histology of tyrannosaurid specimens
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and
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.
</emphasis>
(
<emphasis id="B9352568FFE20E55FC825327FCE1FBD1" bold="true" box="[860,873,1092,1112]" pageId="1" pageNumber="2">A</emphasis>
) Mid-cortex of the transverse thin section of
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.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (
<emphasis id="B9352568FFE20E55FED953F7FE9BFB21" bold="true" box="[263,275,1172,1192]" pageId="1" pageNumber="2">B</emphasis>
) Mid-cortex of the transverse thin section of
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. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(
<emphasis id="B9352568FFE20E55FBBA53A9FBF8FB57" bold="true" box="[1124,1136,1226,1246]" pageId="1" pageNumber="2">C</emphasis>
) Longitudinal section of the mid-cortex of
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.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse section, the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (
<emphasis id="B9352568FFE20E55FE525257FE12FAC1" bold="true" box="[396,410,1332,1352]" pageId="1" pageNumber="2">D</emphasis>
) On the posteromedial side of the transverse section of
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, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(
<emphasis id="B9352568FFE20E55FD57522CFD1CFAEA" bold="true" box="[649,660,1359,1379]" pageId="1" pageNumber="2">E</emphasis>
) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae.
</paragraph>
</caption>
<paragraph id="8BFEF97AFFE20E55FF5E52A9FD19F8AC" blockId="1.[96,777,1482,1887]" pageId="1" pageNumber="2">
In the tibia transverse section of
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(
<figureCitation id="137AE5FFFFE20E55FDB052A9FD30FA6B" box="[622,696,1482,1506]" captionStart="Fig" captionStartId="2.[96,126,773,793]" captionTargetBox="[313,1271,161,757]" captionTargetId="figure@2.[312,1272,160,758]" captionTargetPageId="2" captionText="Fig. 2. Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canalsι the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories." figureDoi="http://doi.org/10.5281/zenodo.3749028" httpUri="https://zenodo.org/record/3749028/files/figure.png" pageId="1" pageNumber="2">Fig. 2A</figureCitation>
and
<httpUri id="B5C027D0FFE20E55FD3652A9FFF3FA76" httpUri="https://advances.sciencemag.org/content/suppl/2019/12/20/6.1.eaax6250.DC1" pageId="1" pageNumber="2">fig. S4</httpUri>
), longitudinal primary osteons are isotropic in circularly polarized light (CPL), but fibers of primary osteons encircling laminar, circular, and plexiform vascular canals are anisotropic. In contrast, primary osteons in the tibia of
<materialsCitation id="3B29F327FFE20E55FE7D5123FDCBF9DE" ID-GBIF-Occurrence="3396425340" box="[419,579,1599,1623]" collectionCode="BMRP" pageId="1" pageNumber="2" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
are frequently isotropic regardless of vascular canal orientation. Because of its proximal sampling location, the cortical shape of the tibia from
<materialsCitation id="3B29F327FFE20E55FD1A5119FF39F926" ID-GBIF-Occurrence="3396425347" collectionCode="BMRP" pageId="1" pageNumber="2" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
in transverse section differs from that of
<materialsCitation id="3B29F327FFE20E55FD9A51FBFD54F926" ID-GBIF-Occurrence="3396425397" box="[580,732,1687,1711]" collectionCode="BMRP" pageId="1" pageNumber="2" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and incorporates the fibular crest on the lateral side (
<httpUri id="B5C027D0FFE20E55FD9951D6FF15F963" httpUri="https://advances.sciencemag.org/content/suppl/2019/12/20/6.1.eaax6250.DC1" pageId="1" pageNumber="2">figs. S2D and S8, A and F</httpUri>
). Highly vascularized reticular woven tissue is present on the anterior and anterolateral periosteal surfaces (
<figureCitation id="137AE5FFFFE20E55FDE9518CFD0DF88E" box="[567,645,1775,1799]" captionStart="Fig" captionStartId="2.[96,126,773,793]" captionTargetBox="[313,1271,161,757]" captionTargetId="figure@2.[312,1272,160,758]" captionTargetPageId="2" captionText="Fig. 2. Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canalsι the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories." figureDoi="http://doi.org/10.5281/zenodo.3749028" httpUri="https://zenodo.org/record/3749028/files/figure.png" pageId="1" pageNumber="2">Fig. 2C</figureCitation>
). In both individuals, the thickest tibial cortex is located anteriorly.
</paragraph>
<paragraph id="8BFEF97AFFE20E55FF5E5049FC14F9DE" blockId="1.[96,777,1482,1887]" lastBlockId="1.[808,1488,1482,1888]" pageId="1" pageNumber="2">
Of special note, within the medullary cavity of the femur and tibia of
<materialsCitation id="3B29F327FFE20E55FFA7502BFE9DF8D6" ID-GBIF-Occurrence="3396425398" box="[121,277,1863,1887]" collectionCode="BMRP" pageId="1" pageNumber="2" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, isotropic, vascularized, primary tissue is separated from the cortex by a lamellar endosteal layer. These features are morphologically consistent with medullary bone (
<bibRefCitation id="EFD0848BFFE20E55FADB5284FA96FA76" author="M. H. Schweitzer &amp; W. Zheng &amp; L. Zanno &amp; S. Werning &amp; T. Sugiyama" box="[1285,1310,1511,1535]" journalOrPublisher="sci. Rep." pageId="1" pageNumber="2" pagination="23099" part="6" refId="ref7543" refString="11. M. H. Schweitzer, W. Zheng, L. Zanno, S. Werning, T. Sugiyama, Chemistry supports the identification of gender-specific reproductive tissue in Tyrannosaurus rex. sci. Rep. 6, 23099 (2016)." title="Chemistry supports the identification of gender-specific reproductive tissue in Tyrannosaurus rex" type="journal article" year="2016">
<emphasis id="B9352568FFE20E55FADB5284FA96FA76" box="[1285,1310,1511,1535]" italics="true" pageId="1" pageNumber="2">11</emphasis>
</bibRefCitation>
); however, additional studies on the systemic nature of this tissue throughout
<materialsCitation id="3B29F327FFE20E55FA535166FCF3F9B3" ID-GBIF-Occurrence="3396425339" collectionCode="BMRP" pageId="1" pageNumber="2" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
and biochemical tests on this tissue are necessary to test this hypothesis.
</paragraph>
<paragraph id="8BFEF97AFFE20E56FC96513EFE92FABB" blockId="1.[808,1488,1482,1888]" lastBlockId="2.[96,777,1071,1888]" lastPageId="2" lastPageNumber="3" pageId="1" pageNumber="2">
Cyclical growth marks (CGMs), resembling tree rings in transverse thin section, were observed in the femora and tibiae of both BMRP specimens. Studies on extant vertebrates demonstrate that CGMs result from brief interruptions in osteogenesis, occurring with annual periodicity and typically coinciding with the nadir (
<bibRefCitation id="EFD0848BFFE20E55FAA251B1FA1CF963" author="M. Kohler &amp; N. Marin-Moratalla &amp; X. Jordana &amp; R. Aanes" box="[1404,1428,1746,1770]" journalOrPublisher="Nature" pageId="1" pageNumber="2" pagination="358 - 361" part="487" refId="ref7590" refString="12. M. Kohler, N. Marin-Moratalla, X. Jordana, R. Aanes, Seasonal bone growth and physiology in endotherms shed light on dinosaur physiology. Nature 487, 358 - 361 (2012)." title="Seasonal bone growth and physiology in endotherms shed light on dinosaur physiology" type="journal article" year="2012">
<emphasis id="B9352568FFE20E55FAA251B1FA1CF963" box="[1404,1428,1746,1770]" italics="true" pageId="1" pageNumber="2">12</emphasis>
</bibRefCitation>
). The annual pauses in bone apposition are recorded as CGMs in cortical microstructure as either pronounced lines of arrested growth (LAGs) or diffuse annulus rings. On the basis of counting CGMs,
<materialsCitation id="3B29F327FFE20E55FA555049FCF5F8D6" ID-GBIF-Occurrence="3396425345" collectionCode="BMRP" pageId="1" pageNumber="2" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
was at least 13 years old at death (13 CGMs in the femur and 10 CGMs in the tibia), and
<materialsCitation id="3B29F327FFE10E56FE405353FDB3FBC1" ID-GBIF-Occurrence="3396425346" box="[414,571,1072,1096]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
was at least 15 years old at death (15 CGMs in the femur and 13 to 18 CGMs in the tibia). Typically, vertebrate long bone cortices will exhibit widely spaced CGMs within the cortex when young, corresponding to high annual osteogenesis. In subadults, CGMs become more closely spaced as osteogenesis decreases approaching adult size [e.g., (
<bibRefCitation id="EFD0848BFFE10E56FDB953A1FDF7FB53" author="K. Padian &amp; E. - T. Lamm" box="[615,639,1218,1242]" journalOrPublisher="University of California Press, Berkeley" pageId="2" pageNumber="3" pagination="285" refId="ref7502" refString="10. K. Padian, E. - T. Lamm, Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation (University of California Press, Berkeley, 2013), p. 285." title="Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation" type="book chapter" year="2013">
<emphasis id="B9352568FFE10E56FDB953A1FDF7FB53" box="[615,639,1218,1242]" italics="true" pageId="2" pageNumber="3">10</emphasis>
</bibRefCitation>
)]. In contrast to these frequently observed patterns, the spacing of CGMs was unexpectedly variable throughout the femur and tibia cortices of both BMRP specimens.
</paragraph>
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<paragraph id="8BFEF97AFFE10E56FFBE5466FCF2FC66" blockId="2.[96,1490,773,1007]" pageId="2" pageNumber="3">
<emphasis id="B9352568FFE10E56FFBE5466FCD7FC90" bold="true" box="[96,863,773,793]" pageId="2" pageNumber="3">
Fig. 2. Tibia histology of tyrannosaurid specimens
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and
<materialsCitation id="3B29F327FFE10E56FD0D5466FCD3FC90" ID-GBIF-Occurrence="3396425318" box="[723,859,773,793]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
.
</emphasis>
(
<emphasis id="B9352568FFE10E56FCB75466FCFEFC90" bold="true" box="[873,886,773,793]" pageId="2" pageNumber="3">A</emphasis>
) Transverse mid-cortex thin section of
<materialsCitation id="3B29F327FFE10E56FB625465FAB1FC93" ID-GBIF-Occurrence="3396425401" box="[1212,1337,774,794]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (
<emphasis id="B9352568FFE10E56FFB85436FFFAFCE0" bold="true" box="[102,114,853,873]" pageId="2" pageNumber="3">B</emphasis>
) Longitudinal thin section of the mid-cortex of
<materialsCitation id="3B29F327FFE10E56FE225435FDF0FCE3" ID-GBIF-Occurrence="3396425335" box="[508,632,854,874]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canals, the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (
<emphasis id="B9352568FFE10E56FD2854C6FC8AFC30" bold="true" box="[758,770,933,953]" pageId="2" pageNumber="3">C</emphasis>
) In transverse thin section, the periosteal surface of
<materialsCitation id="3B29F327FFE10E56FB6E54C5FAA2FC33" ID-GBIF-Occurrence="3396425421" box="[1200,1322,934,954]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(
<emphasis id="B9352568FFE10E56FD1D54A3FD59FC5D" bold="true" box="[707,721,960,980]" pageId="2" pageNumber="3">D</emphasis>
) Within the anterior and anteromedial innermost cortex of
<materialsCitation id="3B29F327FFE10E56FB6354A3FAB0FC5D" ID-GBIF-Occurrence="3396425403" box="[1213,1336,960,980]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories.
</paragraph>
</caption>
<paragraph id="8BFEF97AFFE10E56FF5E525BFE81F994" blockId="2.[96,777,1071,1888]" pageId="2" pageNumber="3">
In the femur of
<materialsCitation id="3B29F327FFE10E56FEFD525BFE4BFAD9" ID-GBIF-Occurrence="3396425357" box="[291,451,1336,1360]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, there is an annulus at the periosteal surface on the medial side (
<figureCitation id="137AE5FFFFE10E56FE695236FD8DFAE4" box="[439,517,1365,1389]" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="2" pageNumber="3">Fig. 1D</figureCitation>
), but when followed posteriorly, the annulus is within the outer cortex, while fibrolamellar tissue makes up the cortex of the periosteal surface (
<figureCitation id="137AE5FFFFE10E56FDBB52F3FD25FA21" box="[613,685,1424,1448]" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="2" pageNumber="3">Fig. 1E</figureCitation>
). Within the innermost cortex on the anterolateral side, six LAGs are closely spaced (
<figureCitation id="137AE5FFFFE10E56FF6A52A9FE8EFA6B" box="[180,262,1482,1506]" captionStart="Fig" captionStartId="2.[96,126,773,793]" captionTargetBox="[313,1271,161,757]" captionTargetId="figure@2.[312,1272,160,758]" captionTargetPageId="2" captionText="Fig. 2. Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canalsι the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories." figureDoi="http://doi.org/10.5281/zenodo.3749028" httpUri="https://zenodo.org/record/3749028/files/figure.png" pageId="2" pageNumber="3">Fig. 2D</figureCitation>
). Because of resorption from the medullary drift, these LAGs are absent within the innermost cortex of the posterior and lateral sides.
</paragraph>
<paragraph id="8BFEF97AFFE10E56FF5E5141FB64F989" blockId="2.[96,777,1071,1888]" lastBlockId="2.[808,1489,1072,1536]" pageId="2" pageNumber="3">
Prondvai
<emphasis id="B9352568FFE10E56FF385140FE91F9B3" box="[230,281,1570,1594]" italics="true" pageId="2" pageNumber="3">et al.</emphasis>
(
<bibRefCitation id="EFD0848BFFE10E56FEF65140FEC8F9B2" author="E. Prondvai &amp; K. H. W. Stein &amp; A. de Ricqles &amp; J. Cubo" box="[296,320,1571,1595]" journalOrPublisher="Biol. J. Linn. soc." pageId="2" pageNumber="3" pagination="799 - 816" part="112" refId="ref7631" refString="13. E. Prondvai, K. H. W. Stein, A. de Ricqles, J. Cubo, Development-based revision of bone tissue classification: the importance of semantics for science. Biol. J. Linn. soc. 112, 799 - 816 (2014)." title="Development-based revision of bone tissue classification: the importance of semantics for science" type="journal article" year="2014">
<emphasis id="B9352568FFE10E56FEF65140FEC8F9B2" box="[296,320,1571,1595]" italics="true" pageId="2" pageNumber="3">13</emphasis>
</bibRefCitation>
) demonstrated that inaccurate bone microstructure interpretations are possible if the mineralized tissue is observed in only a single plane; specifically, the more slowly formed parallel-fibered mineral arrangement could be mistaken for the rapidly deposited woven-fibered mineral arrangement, which has direct bearing on growth rate interpretations. Therefore, the femur of
<materialsCitation id="3B29F327FFE10E56FD1B51D5FF27F963" ID-GBIF-Occurrence="3396425337" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
was longitudinally sectioned in an anterolateral-posteromedial plane, and the tibia of
<materialsCitation id="3B29F327FFE10E56FEEA5193FE43F881" ID-GBIF-Occurrence="3396425388" box="[308,459,1776,1800]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
was sectioned in a medial-lateral plane to accurately assess tissue organization and associated relative growth rates (
<figureCitation id="137AE5FFFFE10E56FF325049FEC8F8CA" box="[236,320,1834,1859]" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="2" pageNumber="3">Figs. 1C</figureCitation>
and
<figureCitation id="137AE5FFFFE10E56FEAC5048FE06F8CA" box="[370,398,1835,1859]" captionStart="Fig" captionStartId="2.[96,126,773,793]" captionTargetBox="[313,1271,161,757]" captionTargetId="figure@2.[312,1272,160,758]" captionTargetPageId="2" captionText="Fig. 2. Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canalsι the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories." figureDoi="http://doi.org/10.5281/zenodo.3749028" httpUri="https://zenodo.org/record/3749028/files/figure.png" pageId="2" pageNumber="3">2B</figureCitation>
, and
<httpUri id="B5C027D0FFE10E56FE1B5049FD68F8CA" box="[453,736,1834,1859]" httpUri="https://advances.sciencemag.org/content/suppl/2019/12/20/6.1.eaax6250.DC1" pageId="2" pageNumber="3">figs. S2, B and C, S5, and S7</httpUri>
). In the femur of
<materialsCitation id="3B29F327FFE10E56FF36502BFE01F8E9" ID-GBIF-Occurrence="3396425315" box="[232,393,1864,1888]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, vascular canals are arranged parallel to the plane of section and to the shaft of the long bone. Adjacent to the vascular canals, bone fibers are highly anisotropic in CPL and contain osteocyte lacunae with long axes arranged parallel to the vascular canals and plane of section. Tissue of the laminae between primary osteons varies locally in degree of isotropy, with corresponding variable shape in osteocyte lacunae. On the medial side of the longitudinal section through the tibia of
<materialsCitation id="3B29F327FFE10E56FB105383FAF9FB71" ID-GBIF-Occurrence="3396425377" box="[1230,1393,1248,1272]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
, vascular canals are arranged obliquely with numerous communications (
<httpUri id="B5C027D0FFE10E56FAA5539EFA4EFA9C" box="[1403,1478,1277,1301]" httpUri="https://advances.sciencemag.org/content/suppl/2019/12/20/6.1.eaax6250.DC1" pageId="2" pageNumber="3">fig.S5B</httpUri>
). From the mid- to the outer cortex, vascular canals are more uniformly parallel to the bone shaft, with fewer transverse Volkmann’s canals (
<httpUri id="B5C027D0FFE10E56FCF15236FC0AFAE4" box="[815,898,1365,1389]" httpUri="https://advances.sciencemag.org/content/suppl/2019/12/20/6.1.eaax6250.DC1" pageId="2" pageNumber="3">fig. S5C</httpUri>
). Adjacent to vascular canals, fibers of the primary osteons are anisotropic in CPL with longitudinally flattened osteocyte lacunae. Fibers within the primary laminae vary locally in isotropy and osteocyte lacuna orientation (
<figureCitation id="137AE5FFFFE10E56FB8852CEFB2AFA4C" box="[1110,1186,1453,1477]" captionStart="Fig" captionStartId="2.[96,126,773,793]" captionTargetBox="[313,1271,161,757]" captionTargetId="figure@2.[312,1272,160,758]" captionTargetPageId="2" captionText="Fig. 2. Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canalsι the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories." figureDoi="http://doi.org/10.5281/zenodo.3749028" httpUri="https://zenodo.org/record/3749028/files/figure.png" pageId="2" pageNumber="3">Fig. 2B</figureCitation>
). The lateral cortex is thinner than the medial cortex, and vascular canals are more closely spaced with fewer communicating canals (
<httpUri id="B5C027D0FFE10E56FB55528BFB68F989" box="[1163,1248,1512,1536]" httpUri="https://advances.sciencemag.org/content/suppl/2019/12/20/6.1.eaax6250.DC1" pageId="2" pageNumber="3">fig. S5D</httpUri>
).
</paragraph>
</subSubSection>
<subSubSection id="C35BAAF1FFE10E56FCF65123FC26F9DE" box="[808,942,1600,1623]" pageId="2" pageNumber="3" type="discussion">
<paragraph id="8BFEF97AFFE10E56FCF65123FC26F9DE" blockId="2.[808,1488,1600,1888]" box="[808,942,1600,1623]" pageId="2" pageNumber="3">
<heading id="D0B64E16FFE10E56FCF65123FC26F9DE" allCaps="true" bold="true" box="[808,942,1600,1623]" fontSize="9" level="2" pageId="2" pageNumber="3" reason="6">
<emphasis id="B9352568FFE10E56FCF65123FC26F9DE" bold="true" box="[808,942,1600,1623]" pageId="2" pageNumber="3">DISCUSSION</emphasis>
</heading>
</paragraph>
</subSubSection>
<paragraph id="8BFEF97AFFE10E56FCF65138FC51F91B" blockId="2.[808,1488,1600,1888]" pageId="2" pageNumber="3">
<heading id="D0B64E16FFE10E56FCF65138FC51F91B" bold="true" fontSize="10" level="3" pageId="2" pageNumber="3" reason="0">
<emphasis id="B9352568FFE10E56FCF65138FC51F91B" bold="true" pageId="2" pageNumber="3">Limb bones exhibit moderate growth rates and tension loading</emphasis>
</heading>
</paragraph>
<paragraph id="8BFEF97AFFE10E57FCF651FBFD47FEE2" blockId="2.[808,1488,1600,1888]" lastBlockId="3.[96,777,160,656]" lastPageId="3" lastPageNumber="4" pageId="2" pageNumber="3">
Comparison of
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and
<materialsCitation id="3B29F327FFE10E56FB4251FBFAB3F939" ID-GBIF-Occurrence="3396425402" box="[1180,1339,1688,1712]" collectionCode="BMRP" pageId="2" pageNumber="3" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
bone fiber organization in the transverse and longitudinal sections using CPL confirms that primary tissue is generally poorly organized parallel fibered to weakly woven. Dense osteocyte lacunae and poor bone fiber organization, in combination with a rich vascular network of reticular, laminar, and plexiform primary osteons, are characteristics that empirically correspond to elevated osteogenesis ranging from 5 to 90 μ m/day (
<bibRefCitation id="EFD0848BFFE00E57FF3C57C0FF72FF32" author="K. Padian &amp; E. - T. Lamm" box="[226,250,163,187]" journalOrPublisher="University of California Press, Berkeley" pageId="3" pageNumber="4" pagination="285" refId="ref7502" refString="10. K. Padian, E. - T. Lamm, Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation (University of California Press, Berkeley, 2013), p. 285." title="Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation" type="book chapter" year="2013">
<emphasis id="B9352568FFE00E57FF3C57C0FF72FF32" box="[226,250,163,187]" italics="true" pageId="3" pageNumber="4">10</emphasis>
</bibRefCitation>
). Nonetheless, the frequency of longitudinal vascularity, as well as regionally prevalent poorly organized parallel fiber bundles within the transverse sections, suggests that annual growth rates were nearer the lower bound (
<bibRefCitation id="EFD0848BFFE00E57FE195798FE57FE9A" author="K. Padian &amp; E. - T. Lamm" box="[455,479,251,275]" journalOrPublisher="University of California Press, Berkeley" pageId="3" pageNumber="4" pagination="285" refId="ref7502" refString="10. K. Padian, E. - T. Lamm, Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation (University of California Press, Berkeley, 2013), p. 285." title="Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation" type="book chapter" year="2013">
<emphasis id="B9352568FFE00E57FE195798FE57FE9A" box="[455,479,251,275]" italics="true" pageId="3" pageNumber="4">10</emphasis>
</bibRefCitation>
). The BMRP individuals did, however, experience occasional periods of faster growth indicated by bands of regionally isotropic woven laminae with reticular vascularity (e.g.,
<figureCitation id="137AE5FFFFE00E57FF685631FE8EFEE2" box="[182,262,338,363]" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="3" pageNumber="4">Figs. 1E</figureCitation>
and
<figureCitation id="137AE5FFFFE00E57FEE65630FEDFFEE2" box="[312,343,339,363]" captionStart="Fig" captionStartId="2.[96,126,773,793]" captionTargetBox="[313,1271,161,757]" captionTargetId="figure@2.[312,1272,160,758]" captionTargetPageId="2" captionText="Fig. 2. Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canalsι the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories." figureDoi="http://doi.org/10.5281/zenodo.3749028" httpUri="https://zenodo.org/record/3749028/files/figure.png" pageId="3" pageNumber="4">2C</figureCitation>
, and
<httpUri id="B5C027D0FFE00E57FE525631FD1AFEE2" box="[396,658,338,363]" httpUri="https://advances.sciencemag.org/content/suppl/2019/12/20/6.1.eaax6250.DC1" pageId="3" pageNumber="4">figs. S6D and S8, C and D</httpUri>
) (
<bibRefCitation id="EFD0848BFFE00E57FD765630FD48FEE2" author="K. Padian &amp; E. - T. Lamm" box="[680,704,339,363]" journalOrPublisher="University of California Press, Berkeley" pageId="3" pageNumber="4" pagination="285" refId="ref7502" refString="10. K. Padian, E. - T. Lamm, Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation (University of California Press, Berkeley, 2013), p. 285." title="Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation" type="book chapter" year="2013">
<emphasis id="B9352568FFE00E57FD765630FD48FEE2" box="[680,704,339,363]" italics="true" pageId="3" pageNumber="4">10</emphasis>
</bibRefCitation>
).
</paragraph>
<paragraph id="8BFEF97AFFE00E57FF5E5613FD46FD19" blockId="3.[96,777,160,656]" pageId="3" pageNumber="4">
In both BMRP specimens, the majority of primary osteons as well as some secondary osteons were isotropic in the transverse section. Corresponding anisotropy in longitudinal examination confirms that the fiber bundles within osteons are longitudinally arranged (
<figureCitation id="137AE5FFFFE00E57FD0956ABFFF5FE74" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="3" pageNumber="4">Figs. 1C</figureCitation>
and
<figureCitation id="137AE5FFFFE00E57FF6C5686FF47FE74" box="[178,207,485,509]" captionStart="Fig" captionStartId="2.[96,126,773,793]" captionTargetBox="[313,1271,161,757]" captionTargetId="figure@2.[312,1272,160,758]" captionTargetPageId="2" captionText="Fig. 2. Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canalsι the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories." figureDoi="http://doi.org/10.5281/zenodo.3749028" httpUri="https://zenodo.org/record/3749028/files/figure.png" pageId="3" pageNumber="4">2B</figureCitation>
, and
<httpUri id="B5C027D0FFE00E57FED75686FE15FE74" box="[265,413,485,509]" httpUri="https://advances.sciencemag.org/content/suppl/2019/12/20/6.1.eaax6250.DC1" pageId="3" pageNumber="4">fig. S5, B to D</httpUri>
). Studies on long bone response to loading show that longitudinal collagen fiber orientation within secondary osteons is commonly found in habitually tension-loaded regions (
<bibRefCitation id="EFD0848BFFE00E57FF67555EFF59FDDC" author="J. G. Skedros &amp; S. D. Mendenhall &amp; C. J. Kiser &amp; H. Winet" box="[185,209,573,597]" journalOrPublisher="Bone" pageId="3" pageNumber="4" pagination="392 - 403" part="44" refId="ref7685" refString="14. J. G. Skedros, S. D. Mendenhall, C. J. Kiser, H. Winet, Interpreting cortical bone adaptation and load history by quantifying osteon morphotypes in circularly polarized light images. Bone 44, 392 - 403 (2009)." title="Interpreting cortical bone adaptation and load history by quantifying osteon morphotypes in circularly polarized light images" type="journal article" year="2009">
<emphasis id="B9352568FFE00E57FF67555EFF59FDDC" box="[185,209,573,597]" italics="true" pageId="3" pageNumber="4">14</emphasis>
</bibRefCitation>
), which may also apply to primary osteon collagen fiber orientation. As such, future studies on tyrannosaurid locomotion biomechanics may benefit from incorporation of osteohistology.
</paragraph>
<paragraph id="8BFEF97AFFE00E57FFBE55D2FE08FD43" blockId="3.[96,777,689,1272]" box="[96,384,689,714]" pageId="3" pageNumber="4">
<heading id="D0B64E16FFE00E57FFBE55D2FE08FD43" bold="true" box="[96,384,689,714]" fontSize="10" level="3" pageId="3" pageNumber="4" reason="0">
<emphasis id="B9352568FFE00E57FFBE55D2FE08FD43" bold="true" box="[96,384,689,714]" pageId="3" pageNumber="4">Relative skeletal maturity</emphasis>
</heading>
</paragraph>
<paragraph id="8BFEF97AFFE00E57FFBE55B3FE88FB71" blockId="3.[96,777,689,1272]" pageId="3" pageNumber="4">
Rather than exhibiting an external fundamental system (EFS) (
<figureCitation id="137AE5FFFFE00E57FD1D55B3FD73FD61" box="[707,763,720,744]" captionStart="Fig" captionStartId="3.[808,838,1079,1099]" captionTargetBox="[813,1484,161,1063]" captionTargetId="figure@3.[812,1484,160,1064]" captionTargetPageId="3" captionText="Fig. 3. The presence of an EFS at the periosteal surface of a long bone indicates skeletal maturity, while the absence of an EFS indicates that the bone is still growing at the time of death. (A) An EFS composed of tightly stacked birefringent LAGs (between blue arrowheads) at the periosteal surface of an Alligator mississippiensis. (B) The EFS (between blue arrowheads) in an ostrich (struthio camelus) is made of nearly avascular, birefringent parallel-fibered to lamellar primary tissue.(C) No EFS is present at the periosteal surface of the femur of BMRP 2002.4.1, (D) the tibia of BMRP 2002.4.1, (E) the femur of BMRP 2006.4.4, or (F) the tibia of BMRP 2006.4.4.All panels are shown in transverse thin section, with CPL." figureDoi="http://doi.org/10.5281/zenodo.3749030" httpUri="https://zenodo.org/record/3749030/files/figure.png" pageId="3" pageNumber="4">Fig. 3</figureCitation>
), a woven-parallel complex extends to the periosteal surface in both tyrannosaurid specimens. Thus, histology supports morphological observations that
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and
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were skeletally immature individuals at death (
<bibRefCitation id="EFD0848BFFE00E57FE4C5426FE21FCD4" author="K. Padian &amp; E. - T. Lamm" box="[402,425,837,861]" journalOrPublisher="University of California Press, Berkeley" pageId="3" pageNumber="4" pagination="285" refId="ref7502" refString="10. K. Padian, E. - T. Lamm, Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation (University of California Press, Berkeley, 2013), p. 285." title="Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation" type="book chapter" year="2013">
<emphasis id="B9352568FFE00E57FE4C5426FE21FCD4" box="[402,425,837,861]" italics="true" pageId="3" pageNumber="4">10</emphasis>
</bibRefCitation>
). In lieu of epiphyseal fusion, which most reptile taxa lack, an EFS is the only way to conclusively confirm attainment of asymptotic adult body length from the long bones of a vertebrate. When present, the EFS occupies the periosteal surface as either closely spaced LAGs (separated by micrometers) (
<figureCitation id="137AE5FFFFE00E57FD6A54D9FC89FC5A" box="[692,769,954,979]" captionStart="Fig" captionStartId="3.[808,838,1079,1099]" captionTargetBox="[813,1484,161,1063]" captionTargetId="figure@3.[812,1484,160,1064]" captionTargetPageId="3" captionText="Fig. 3. The presence of an EFS at the periosteal surface of a long bone indicates skeletal maturity, while the absence of an EFS indicates that the bone is still growing at the time of death. (A) An EFS composed of tightly stacked birefringent LAGs (between blue arrowheads) at the periosteal surface of an Alligator mississippiensis. (B) The EFS (between blue arrowheads) in an ostrich (struthio camelus) is made of nearly avascular, birefringent parallel-fibered to lamellar primary tissue.(C) No EFS is present at the periosteal surface of the femur of BMRP 2002.4.1, (D) the tibia of BMRP 2002.4.1, (E) the femur of BMRP 2006.4.4, or (F) the tibia of BMRP 2006.4.4.All panels are shown in transverse thin section, with CPL." figureDoi="http://doi.org/10.5281/zenodo.3749030" httpUri="https://zenodo.org/record/3749030/files/figure.png" pageId="3" pageNumber="4">Fig. 3A</figureCitation>
) or as a thick, primarily avascular annulus (
<figureCitation id="137AE5FFFFE00E57FDD854BBFDC6FC79" box="[518,590,984,1008]" captionStart="Fig" captionStartId="3.[808,838,1079,1099]" captionTargetBox="[813,1484,161,1063]" captionTargetId="figure@3.[812,1484,160,1064]" captionTargetPageId="3" captionText="Fig. 3. The presence of an EFS at the periosteal surface of a long bone indicates skeletal maturity, while the absence of an EFS indicates that the bone is still growing at the time of death. (A) An EFS composed of tightly stacked birefringent LAGs (between blue arrowheads) at the periosteal surface of an Alligator mississippiensis. (B) The EFS (between blue arrowheads) in an ostrich (struthio camelus) is made of nearly avascular, birefringent parallel-fibered to lamellar primary tissue.(C) No EFS is present at the periosteal surface of the femur of BMRP 2002.4.1, (D) the tibia of BMRP 2002.4.1, (E) the femur of BMRP 2006.4.4, or (F) the tibia of BMRP 2006.4.4.All panels are shown in transverse thin section, with CPL." figureDoi="http://doi.org/10.5281/zenodo.3749030" httpUri="https://zenodo.org/record/3749030/files/figure.png" pageId="3" pageNumber="4">Fig. 3B</figureCitation>
) (
<bibRefCitation id="EFD0848BFFE00E57FDBD54BBFDF3FC79" author="K. Padian &amp; E. - T. Lamm" box="[611,635,984,1008]" journalOrPublisher="University of California Press, Berkeley" pageId="3" pageNumber="4" pagination="285" refId="ref7502" refString="10. K. Padian, E. - T. Lamm, Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation (University of California Press, Berkeley, 2013), p. 285." title="Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation" type="book chapter" year="2013">
<emphasis id="B9352568FFE00E57FDBD54BBFDF3FC79" box="[611,635,984,1008]" italics="true" pageId="3" pageNumber="4">10</emphasis>
</bibRefCitation>
). CGMs close to the periosteal surface can sometimes be mistaken for an EFS. In the case of
<materialsCitation id="3B29F327FFE00E57FF0A5370FEFEFBA3" ID-GBIF-Occurrence="3396425390" box="[212,374,1042,1066]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, an annulus is present at the periosteal surface of both the femur (
<figureCitation id="137AE5FFFFE00E57FEB65353FE3CFBC1" box="[360,436,1072,1096]" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="3" pageNumber="4">Fig. 1D</figureCitation>
) and tibia (
<httpUri id="B5C027D0FFE00E57FDFB5353FDFDFBC1" box="[549,629,1072,1096]" httpUri="https://advances.sciencemag.org/content/suppl/2019/12/20/6.1.eaax6250.DC1" pageId="3" pageNumber="4">fig. S8E</httpUri>
), but when the annulus is followed around the cortex, in both cases it becomes embedded within the outer cortex and superseded by woven primary tissue (
<figureCitation id="137AE5FFFFE00E57FF7C53EBFF67FB29" box="[162,239,1160,1184]" captionStart="Fig" captionStartId="1.[96,125,1092,1112]" captionTargetBox="[313,1271,161,1076]" captionTargetId="figure@1.[312,1272,160,1077]" captionTargetPageId="1" captionText="Fig. 1. Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1.Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons.In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL.CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae.(C) Longitudinal section of the mid-cortex of BMRP 2006.4.4.Vascular canals appear as near-vertical, thin, dark columns. As in the transverse sectionι the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line).Photographed in CPL.(E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae." figureDoi="http://doi.org/10.5281/zenodo.3749026" httpUri="https://zenodo.org/record/3749026/files/figure.png" pageId="3" pageNumber="4">Figs. 1E</figureCitation>
and
<figureCitation id="137AE5FFFFE00E57FEC053EBFEB5FB29" box="[286,317,1160,1184]" captionStart="Fig" captionStartId="2.[96,126,773,793]" captionTargetBox="[313,1271,161,757]" captionTargetId="figure@2.[312,1272,160,758]" captionTargetPageId="2" captionText="Fig. 2. Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canalsι the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories." figureDoi="http://doi.org/10.5281/zenodo.3749028" httpUri="https://zenodo.org/record/3749028/files/figure.png" pageId="3" pageNumber="4">2C</figureCitation>
). The proximity of the annulus to the periosteal surface instead suggests that
<materialsCitation id="3B29F327FFE00E57FE5C53C5FD97FB34" ID-GBIF-Occurrence="3396425353" box="[386,543,1189,1213]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
died soon after growth resumed following the annual hiatus and that cortical osteogenesis was directional.
</paragraph>
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<paragraph id="8BFEF97AFFE00E57FCF65354FA49FAA8" blockId="3.[808,1489,1079,1314]" pageId="3" pageNumber="4">
<emphasis id="B9352568FFE00E57FCF65354FBDDFB08" bold="true" pageId="3" pageNumber="4">Fig. 3. The presence of an EFS at the periosteal surface of a long bone indicates skeletal maturity, while the absence of an EFS indicates that the bone is still growing at the time of death.</emphasis>
(
<emphasis id="B9352568FFE00E57FB81530EFBE4FB08" bold="true" box="[1119,1132,1133,1153]" pageId="3" pageNumber="4">A</emphasis>
) An EFS composed of tightly stacked birefringent LAGs (between blue arrowheads) at the periosteal surface of an
<taxonomicName id="4C4182F9FFE00E57FA5753E4FC21FB3F" baseAuthorityName="Daudin" baseAuthorityYear="1802" class="Reptilia" family="Alligatoridae" genus="Alligator" kingdom="Animalia" order="Crocodylia" pageId="3" pageNumber="4" phylum="Chordata" rank="species" species="mississippiensis">
<emphasis id="B9352568FFE00E57FA5753E4FC21FB3F" italics="true" pageId="3" pageNumber="4">Alligator mississippiensis</emphasis>
</taxonomicName>
. (
<emphasis id="B9352568FFE00E57FC6453C1FC4EFB3F" bold="true" box="[954,966,1186,1206]" pageId="3" pageNumber="4">B</emphasis>
) The EFS (between blue arrowheads) in an ostrich (
<emphasis id="B9352568FFE00E57FA5053C1FCE2FB58" italics="true" pageId="3" pageNumber="4">struthio camelus</emphasis>
) is made of nearly avascular, birefringent parallel-fibered to lamellar primary tissue.(
<emphasis id="B9352568FFE00E57FC4853B4FC2AFB62" bold="true" box="[918,930,1239,1259]" pageId="3" pageNumber="4">C</emphasis>
) No EFS is present at the periosteal surface of the femur of BMRP 2002.4.1, (
<emphasis id="B9352568FFE00E57FC5E5391FC06FA8F" bold="true" box="[896,910,1266,1286]" pageId="3" pageNumber="4">D</emphasis>
) the tibia of BMRP 2002.4.1, (
<emphasis id="B9352568FFE00E57FB5E5391FB03FA8F" bold="true" box="[1152,1163,1266,1286]" pageId="3" pageNumber="4">E</emphasis>
) the femur of
<materialsCitation id="3B29F327FFE00E57FADE5390FAF4FA8E" ID-GBIF-Occurrence="3396425395" box="[1280,1404,1267,1287]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, or (
<emphasis id="B9352568FFE00E57FA7E5391FA23FA8F" bold="true" box="[1440,1451,1266,1286]" pageId="3" pageNumber="4">F</emphasis>
) the tibia of
<materialsCitation id="3B29F327FFE00E57FCB9526DFC6CFAAB" ID-GBIF-Occurrence="3396425385" box="[871,996,1294,1314]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
.All panels are shown in transverse thin section, with CPL.
</paragraph>
</caption>
<paragraph id="8BFEF97AFFE00E57FFBE527AFE94FABB" blockId="3.[96,776,1305,1888]" box="[96,284,1305,1330]" pageId="3" pageNumber="4">
<heading id="D0B64E16FFE00E57FFBE527AFE94FABB" bold="true" box="[96,284,1305,1330]" fontSize="10" level="3" pageId="3" pageNumber="4" reason="0">
<emphasis id="B9352568FFE00E57FFBE527AFE94FABB" bold="true" box="[96,284,1305,1330]" pageId="3" pageNumber="4">Ontogenetic age</emphasis>
</heading>
</paragraph>
<paragraph id="8BFEF97AFFE00E57FFBE525BFEEAF9FC" blockId="3.[96,776,1305,1888]" pageId="3" pageNumber="4">
On the basis of femur CGM count,
<materialsCitation id="3B29F327FFE00E57FE62525BFDDEFAD9" ID-GBIF-Occurrence="3396425334" box="[444,598,1336,1360]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
was&gt;13 years old at death, which is 2 years older than the original estimate by Erickson (
<bibRefCitation id="EFD0848BFFE00E57FFB75210FFFDFA02" author="G. M. Erickson" box="[105,117,1395,1419]" journalOrPublisher="Trends Ecol. Evol." pageId="3" pageNumber="4" pagination="677 - 684" part="20" refId="ref7429" refString="8. G. M. Erickson, Assessing dinosaur growth patterns: A microscopic revolution. Trends Ecol. Evol. 20, 677 - 684 (2005)." title="Assessing dinosaur growth patterns: A microscopic revolution" type="journal article" year="2005">
<emphasis id="B9352568FFE00E57FFB75210FFFDFA02" box="[105,117,1395,1419]" italics="true" pageId="3" pageNumber="4">8</emphasis>
</bibRefCitation>
) based on fibula CGM count. The slightly larger
<materialsCitation id="3B29F327FFE00E57FDB45210FC80FA03" ID-GBIF-Occurrence="3396425325" box="[618,776,1394,1418]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
was&gt;15 years old. The number of CGMs missing due to medullary expansion is unknown, precluding an exact age at death for
<materialsCitation id="3B29F327FFE00E57FD1B52CDFF39FA6A" ID-GBIF-Occurrence="3396425413" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
<materialsCitation id="3B29F327FFE00E57FF3E52A8FEF3FA6B" ID-GBIF-Occurrence="3396425389" box="[224,379,1482,1506]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
. Although the number of missing CGMs could be predicted on the basis of innermost zonal thicknesses and a process of retrocalculation [e.g., (
<bibRefCitation id="EFD0848BFFE00E57FE165165FE5CF994" author="J. R. Horner &amp; K. Padian" box="[456,468,1542,1565]" journalOrPublisher="Proc. R. soc. Lond. B Biol. sci." pageId="3" pageNumber="4" pagination="1875 - 1880" part="271" refId="ref7285" refString="5. J. R. Horner, K. Padian, Age and growth dynamics of Tyrannosaurus rex. Proc. R. soc. Lond. B Biol. sci. 271, 1875 - 1880 (2004)." title="Age and growth dynamics of Tyrannosaurus rex" type="journal article" year="2004">
<emphasis id="B9352568FFE00E57FE165165FE5CF994" box="[456,468,1542,1565]" italics="true" pageId="3" pageNumber="4">5</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE00E57FE3E5166FE70F994" author="K. Padian &amp; E. - T. Lamm" box="[480,504,1541,1565]" journalOrPublisher="University of California Press, Berkeley" pageId="3" pageNumber="4" pagination="285" refId="ref7502" refString="10. K. Padian, E. - T. Lamm, Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation (University of California Press, Berkeley, 2013), p. 285." title="Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation" type="book chapter" year="2013">
<emphasis id="B9352568FFE00E57FE3E5166FE70F994" box="[480,504,1541,1565]" italics="true" pageId="3" pageNumber="4">10</emphasis>
</bibRefCitation>
)], the variable spacing between CGMs observed in
<materialsCitation id="3B29F327FFE00E57FEB45140FD81F9B2" ID-GBIF-Occurrence="3396425328" box="[362,521,1571,1595]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
<materialsCitation id="3B29F327FFE00E57FDE25140FD53F9B3" ID-GBIF-Occurrence="3396425331" box="[572,731,1570,1594]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
and other tyrannosaurs (
<bibRefCitation id="EFD0848BFFE00E57FEF55123FECBF9D1" author="L. E. Zanno &amp; R. T. Tucker &amp; A. Canoville &amp; H. M. Avrahami &amp; T. A. Gates &amp; P. J. Makovicky" box="[299,323,1600,1624]" journalOrPublisher="Commun. Biol." pageId="3" pageNumber="4" pagination="64" part="2" refId="ref7736" refString="15. L. E. Zanno, R. T. Tucker, A. Canoville, H. M. Avrahami, T. A. Gates, P. J. Makovicky, Diminutive fleet-footed tyrannosauroid narrows the 70 - million-year gap in the North American fossil record. Commun. Biol. 2, 64 (2019)." title="Diminutive fleet-footed tyrannosauroid narrows the 70 - million-year gap in the North American fossil record" type="journal article" year="2019">
<emphasis id="B9352568FFE00E57FEF55123FECBF9D1" box="[299,323,1600,1624]" italics="true" pageId="3" pageNumber="4">15</emphasis>
</bibRefCitation>
) renders the technique unreliable in this case, and it was not attempted.
</paragraph>
<paragraph id="8BFEF97AFFE00E57FF5E5119FBF7F944" blockId="3.[96,776,1305,1888]" lastBlockId="3.[808,1489,1394,1888]" pageId="3" pageNumber="4">
Within the innermost cortex of
<materialsCitation id="3B29F327FFE00E57FE175118FDE2F91B" ID-GBIF-Occurrence="3396425322" box="[457,618,1658,1682]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, there is a tight stacking of six CGMs (
<figureCitation id="137AE5FFFFE00E57FE9951FBFE1EF939" box="[327,406,1688,1712]" captionStart="Fig" captionStartId="2.[96,126,773,793]" captionTargetBox="[313,1271,161,757]" captionTargetId="figure@2.[312,1272,160,758]" captionTargetPageId="2" captionText="Fig. 2. Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4. (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section.Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1.Vascular canals appear as near-vertical, dark columns.Adjacent to the vascular canalsι the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP.Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue.(D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially.Blue lines highlight the LAG trajectories." figureDoi="http://doi.org/10.5281/zenodo.3749028" httpUri="https://zenodo.org/record/3749028/files/figure.png" pageId="3" pageNumber="4">Fig. 2D</figureCitation>
). Because the CGMs remain parallel about the cortex and do not merge, they either represent a single hiatus in which growth repeatedly ceased and resumed (totaling 13 years of growth) or up to 6 years where relatively little growth occurred annually (totaling up to 18 years of growth) (
<bibRefCitation id="EFD0848BFFE00E57FDFC506EFDA6F8AC" author="H. N. Woodward &amp; J. R. Horner &amp; J. O. Farlow" box="[546,558,1805,1829]" journalOrPublisher="PeerJ" pageId="3" pageNumber="4" pagination="e 422" part="2" refId="ref7460" refString="9. H. N. Woodward, J. R. Horner, J. O. Farlow, Quantification of intraskeletal histovariability in Alligator mississippiensis and implications for vertebrate osteohistology. PeerJ 2, e 422 (2014)." title="Quantification of intraskeletal histovariability in Alligator mississippiensis and implications for vertebrate osteohistology" type="journal article" year="2014">
<emphasis id="B9352568FFE00E57FDFC506EFDA6F8AC" box="[546,558,1805,1829]" italics="true" pageId="3" pageNumber="4">9</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE00E57FDE7506EFDD9F8AC" author="M. H. Caetano &amp; J. Castanet" box="[569,593,1805,1829]" journalOrPublisher="Amphibia Reptilia" pageId="3" pageNumber="4" pagination="117 - 129" part="14" refId="ref7799" refString="16. M. H. Caetano, J. Castanet, Variability and microevolutionary patterns in Triturus marmoratus from Portugal: age, size, longevity and individual growth. Amphibia Reptilia 14, 117 - 129 (1993)." title="Variability and microevolutionary patterns in Triturus marmoratus from Portugal: age, size, longevity and individual growth" type="journal article" year="1993">
<emphasis id="B9352568FFE00E57FDE7506EFDD9F8AC" box="[569,593,1805,1829]" italics="true" pageId="3" pageNumber="4">16</emphasis>
</bibRefCitation>
). This tight stacking of six CGMs is not observed in the femur of
<materialsCitation id="3B29F327FFE00E57FDBE5048FC8CF8CB" ID-GBIF-Occurrence="3396425378" box="[608,772,1834,1858]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, which preserves 15 CGMs. The CGM count from the partial tibia of
<materialsCitation id="3B29F327FFE00E57FCF65210FC4CFA03" ID-GBIF-Occurrence="3396425366" box="[808,964,1394,1418]" collectionCode="BMRP" pageId="3" pageNumber="4" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
is questionable because the proximal sampling location away from midshaft incorporates the fibular crest, introducing associated regions of remodeling and directional growth affecting apposition interpretations. Because of this and their absence in the femur, the observed grouping of six CGMs is conservatively interpreted as a single hiatus event. Similar instances of a single hiatus represented by narrowly spaced LAGs are reported in other tyrannosauroids (
<bibRefCitation id="EFD0848BFFE00E57FC545123FC2AF9D1" author="L. E. Zanno &amp; R. T. Tucker &amp; A. Canoville &amp; H. M. Avrahami &amp; T. A. Gates &amp; P. J. Makovicky" box="[906,930,1600,1624]" journalOrPublisher="Commun. Biol." pageId="3" pageNumber="4" pagination="64" part="2" refId="ref7736" refString="15. L. E. Zanno, R. T. Tucker, A. Canoville, H. M. Avrahami, T. A. Gates, P. J. Makovicky, Diminutive fleet-footed tyrannosauroid narrows the 70 - million-year gap in the North American fossil record. Commun. Biol. 2, 64 (2019)." title="Diminutive fleet-footed tyrannosauroid narrows the 70 - million-year gap in the North American fossil record" type="journal article" year="2019">
<emphasis id="B9352568FFE00E57FC545123FC2AF9D1" box="[906,930,1600,1624]" italics="true" pageId="3" pageNumber="4">15</emphasis>
</bibRefCitation>
). If this grouping of CGMs instead represents 6 years of protracted growth, then
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demonstrates the extent to which these individuals could adjust growth rate based on resource availability, in this case prolonging the ontogenetic duration of
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as a mid-sized carnivore.
</paragraph>
<paragraph id="8BFEF97AFFE00E50FC9651B0FE5AFE2C" blockId="3.[808,1489,1394,1888]" lastBlockId="4.[96,777,162,773]" lastPageId="4" lastPageNumber="5" pageId="3" pageNumber="4">
Bone tissue organization was similar across femora and tibiae, suggesting that both bones record annual increases in body size equally well. If the stacked CGMs of
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reflect a single hiatus, then each femur preserved more CGMs than the associated tibia. Previous studies demonstrated that intraskeletal inconsistencies in CGM counts are due to variable rates of medullary cavity expansion or cortical drift across elements (
<bibRefCitation id="EFD0848BFFE70E50FE2E57A3FE74FF51" author="H. N. Woodward &amp; J. R. Horner &amp; J. O. Farlow" box="[496,508,192,216]" journalOrPublisher="PeerJ" pageId="4" pageNumber="5" pagination="e 422" part="2" refId="ref7460" refString="9. H. N. Woodward, J. R. Horner, J. O. Farlow, Quantification of intraskeletal histovariability in Alligator mississippiensis and implications for vertebrate osteohistology. PeerJ 2, e 422 (2014)." title="Quantification of intraskeletal histovariability in Alligator mississippiensis and implications for vertebrate osteohistology" type="journal article" year="2014">
<emphasis id="B9352568FFE70E50FE2E57A3FE74FF51" box="[496,508,192,216]" italics="true" pageId="4" pageNumber="5">9</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE70E50FDD457A3FDAAFF51" author="I. Griffiths" box="[522,546,192,216]" journalOrPublisher="Ann. Mag. Nat. Hist." pageId="4" pageNumber="5" pagination="449 - 465" part="4" refId="ref7841" refString="17. I. Griffiths, Skeletal lamellae as an index of age in Heterothermous Tetrapods. Ann. Mag. Nat. Hist. 4, 449 - 465 (1961)." title="Skeletal lamellae as an index of age in Heterothermous Tetrapods" type="journal article" year="1961">
<emphasis id="B9352568FFE70E50FDD457A3FDAAFF51" box="[522,546,192,216]" italics="true" pageId="4" pageNumber="5">17</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE70E50FDEE57A3FDC0FF51" author="J. M. Hutton" box="[560,584,192,216]" journalOrPublisher="Copeia" pageId="4" pageNumber="5" pagination="332 - 341" part="2" refId="ref7875" refString="18. J. M. Hutton, Age determination of living Nile crocodiles from the cortical stratification of bone. Copeia 2, 332 - 341 (1986)." title="Age determination of living Nile crocodiles from the cortical stratification of bone" type="journal article" year="1986">
<emphasis id="B9352568FFE70E50FDEE57A3FDC0FF51" box="[560,584,192,216]" italics="true" pageId="4" pageNumber="5">18</emphasis>
</bibRefCitation>
) when sampled at midshaft. Therefore, our preliminary assessment of
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<emphasis id="B9352568FFE70E50FDB657BDFD2AFF7C" box="[616,674,222,245]" italics="true" pageId="4" pageNumber="5">T. rex</emphasis>
</taxonomicName>
intraskeletal histology suggests that the femur is more informative than the tibia, despite regions of cortical remodeling from tendinous entheses about the cortex. Additional intraskeletal histoanalyses of tyrannosaurid specimens are necessary to test whether the femur is the preferred weight-bearing bone for simultaneous assessments of annual growth rates and skeletochronology.
</paragraph>
<paragraph id="8BFEF97AFFE70E50FF5E56C8FE5AFC8C" blockId="4.[96,777,162,773]" pageId="4" pageNumber="5">
In addition to ontogenetic zonal thickness variability within the cortex, zonal thickness also changed with respect to cortical orientation. That is, zones were often much thinner relative to one another on one side of the transverse section and much thicker on another side (e.g.,
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). This pattern is particularly noticeable in the tibia of
<materialsCitation id="3B29F327FFE70E50FF12555DFEECFDDC" ID-GBIF-Occurrence="3396425363" box="[204,356,573,597]" collectionCode="BMRP" pageId="4" pageNumber="5" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
(medial cortical zones are thickest) and the femur of
<materialsCitation id="3B29F327FFE70E50FF635538FED0FDFB" ID-GBIF-Occurrence="3396425381" box="[189,344,602,626]" collectionCode="BMRP" pageId="4" pageNumber="5" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
(posteromedial cortical zones are thickest). This observation implies that directional cortical growth occurred over ontogeny and stresses the necessity of complete transverse sections for histological analysis: Obtaining a fragment or core for study from one orientation may result in erroneous interpretations of growth rate and skeletal maturity.
</paragraph>
<paragraph id="8BFEF97AFFE70E50FFBE5445FECDFCD4" blockId="4.[96,777,806,1888]" pageId="4" pageNumber="5">
<heading id="D0B64E16FFE70E50FFBE5445FECDFCD4" bold="true" fontSize="10" level="3" pageId="4" pageNumber="5" reason="0">
<emphasis id="B9352568FFE70E50FFBE5445FECDFCD4" bold="true" pageId="4" pageNumber="5">Variability in annual growth as a response to resource abundance</emphasis>
</heading>
</paragraph>
<paragraph id="8BFEF97AFFE70E50FFBE5400FB24F8E9" blockId="4.[96,777,806,1888]" lastBlockId="4.[808,1489,1806,1888]" pageId="4" pageNumber="5">
Interpretations of relative maturity in nonavian dinosaurs often rely on reported trends in the thickness of cortical zones between CGMs from the inner to the outer cortex (
<bibRefCitation id="EFD0848BFFE70E50FE1354FEFE6DFC3C" author="K. Padian &amp; E. - T. Lamm" box="[461,485,925,949]" journalOrPublisher="University of California Press, Berkeley" pageId="4" pageNumber="5" pagination="285" refId="ref7502" refString="10. K. Padian, E. - T. Lamm, Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation (University of California Press, Berkeley, 2013), p. 285." title="Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation" type="book chapter" year="2013">
<emphasis id="B9352568FFE70E50FE1354FEFE6DFC3C" box="[461,485,925,949]" italics="true" pageId="4" pageNumber="5">10</emphasis>
</bibRefCitation>
). Zone thickness is typically greatest within the innermost cortex, corresponding to rapid annual growth early in life. Zones become progressively thinner in the midto the outer cortex of older individuals, as annual growth rate decreases approaching asymptotic body length. These general trends provide the interpretive foundation for the two previous histologybased ontogenetic studies on
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<emphasis id="B9352568FFE70E50FE40532DFDB5FBEC" box="[414,573,1102,1125]" italics="true" pageId="4" pageNumber="5">Tyrannosaurus</emphasis>
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growth (
<bibRefCitation id="EFD0848BFFE70E50FD7F532EFD25FBEC" author="G. M. Erickson &amp; P. J. Makovicky &amp; P. J. Currie &amp; M. A. Norell &amp; S. A. Yerby &amp; C. A. Brochu" box="[673,685,1101,1125]" journalOrPublisher="Nature" pageId="4" pageNumber="5" pagination="772 - 775" part="430" refId="ref7228" refString="4. G. M. Erickson, P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, C. A. Brochu, Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature 430, 772 - 775 (2004)." title="Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs" type="journal article" year="2004">
<emphasis id="B9352568FFE70E50FD7F532EFD25FBEC" box="[673,685,1101,1125]" italics="true" pageId="4" pageNumber="5">4</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE70E50FD65532DFD4FFBEC" author="J. R. Horner &amp; K. Padian" box="[699,711,1102,1125]" journalOrPublisher="Proc. R. soc. Lond. B Biol. sci." pageId="4" pageNumber="5" pagination="1875 - 1880" part="271" refId="ref7285" refString="5. J. R. Horner, K. Padian, Age and growth dynamics of Tyrannosaurus rex. Proc. R. soc. Lond. B Biol. sci. 271, 1875 - 1880 (2004)." title="Age and growth dynamics of Tyrannosaurus rex" type="journal article" year="2004">
<emphasis id="B9352568FFE70E50FD65532DFD4FFBEC" box="[699,711,1102,1125]" italics="true" pageId="4" pageNumber="5">5</emphasis>
</bibRefCitation>
). The spacing of CGMs within the outer cortices of
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and
<materialsCitation id="3B29F327FFE70E50FFBE53EBFE8FFB29" ID-GBIF-Occurrence="3396425355" box="[96,263,1160,1184]" collectionCode="BMRP" pageId="4" pageNumber="5" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
(
<figureCitation id="137AE5FFFFE70E50FEC953EBFEDEFB29" box="[279,342,1160,1184]" captionStart="Fig" captionStartId="4.[808,838,1591,1611]" captionTargetBox="[813,1484,161,1574]" captionTargetId="figure@4.[812,1484,160,1575]" captionTargetPageId="4" captionText="Fig. 4. Examples of variable CGM (blue lines) spacing in tyrannosaurids examined for this study. (A) The variability of CGM spacing in the femur of BMRP 2002.4.1 and (B) the tibia of BMRP 2006.4.4 may imply that these individuals were approaching asymptotic body length. Howeverι CGMs within the innermost cortices of much larger T.rex specimens (C) USNM PAL 555000 and (D) MOR 1128 demonstrate that the CGM spacing is not a reliable indicator of relative maturity status.All panels are shown in transverse thin section." figureDoi="http://doi.org/10.5281/zenodo.3749032" httpUri="https://zenodo.org/record/3749032/files/figure.png" pageId="4" pageNumber="5">Fig. 4</figureCitation>
) is narrower than between some CGMs deeper within the cortices, which suggests that, although not adults, the specimens were approaching a body length asymptote at about one-half the body length of
<materialsCitation id="3B29F327FFE70E50FEAA5383FD91FB71" ID-GBIF-Occurrence="3396425341" box="[372,537,1248,1272]" collectionCode="FMNH" pageId="4" pageNumber="5" specimenCode="FMNH PR2081">FMNH PR 2081</materialsCitation>
. However, annual zonal thicknesses between CGMs deeper within the cortices of
<materialsCitation id="3B29F327FFE70E50FD1D539DFF3EFABA" ID-GBIF-Occurrence="3396425374" collectionCode="BMRP" pageId="4" pageNumber="5" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
(
<figureCitation id="137AE5FFFFE70E50FF1B5278FE9CFABA" box="[197,276,1307,1331]" captionStart="Fig" captionStartId="4.[808,838,1591,1611]" captionTargetBox="[813,1484,161,1574]" captionTargetId="figure@4.[812,1484,160,1575]" captionTargetPageId="4" captionText="Fig. 4. Examples of variable CGM (blue lines) spacing in tyrannosaurids examined for this study. (A) The variability of CGM spacing in the femur of BMRP 2002.4.1 and (B) the tibia of BMRP 2006.4.4 may imply that these individuals were approaching asymptotic body length. Howeverι CGMs within the innermost cortices of much larger T.rex specimens (C) USNM PAL 555000 and (D) MOR 1128 demonstrate that the CGM spacing is not a reliable indicator of relative maturity status.All panels are shown in transverse thin section." figureDoi="http://doi.org/10.5281/zenodo.3749032" httpUri="https://zenodo.org/record/3749032/files/figure.png" pageId="4" pageNumber="5">Fig. 4A</figureCitation>
) and
<materialsCitation id="3B29F327FFE70E50FE8E5278FE7AFABA" ID-GBIF-Occurrence="3396425348" box="[336,498,1307,1331]" collectionCode="BMRP" pageId="4" pageNumber="5" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
(
<figureCitation id="137AE5FFFFE70E50FDDE5278FDC5FABA" box="[512,589,1307,1331]" captionStart="Fig" captionStartId="4.[808,838,1591,1611]" captionTargetBox="[813,1484,161,1574]" captionTargetId="figure@4.[812,1484,160,1575]" captionTargetPageId="4" captionText="Fig. 4. Examples of variable CGM (blue lines) spacing in tyrannosaurids examined for this study. (A) The variability of CGM spacing in the femur of BMRP 2002.4.1 and (B) the tibia of BMRP 2006.4.4 may imply that these individuals were approaching asymptotic body length. Howeverι CGMs within the innermost cortices of much larger T.rex specimens (C) USNM PAL 555000 and (D) MOR 1128 demonstrate that the CGM spacing is not a reliable indicator of relative maturity status.All panels are shown in transverse thin section." figureDoi="http://doi.org/10.5281/zenodo.3749032" httpUri="https://zenodo.org/record/3749032/files/figure.png" pageId="4" pageNumber="5">Fig. 4B</figureCitation>
) are variable, and zones do not consistently progress from widely spaced within the inner cortex to more closely spaced in the outer cortex. Because of unpredictable spacing within the cortex, reduced zonal thickness near the periosteal surface is likely an unreliable indicator of skeletal maturity in
<materialsCitation id="3B29F327FFE70E50FF3E52CDFE0DFA4C" ID-GBIF-Occurrence="3396425314" box="[224,389,1453,1477]" collectionCode="BMRP" pageId="4" pageNumber="5" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
<materialsCitation id="3B29F327FFE70E50FE6252CDFDECFA4C" ID-GBIF-Occurrence="3396425368" box="[444,612,1453,1477]" collectionCode="BMRP" pageId="4" pageNumber="5" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
. Variable zonal thicknesses are, thus, likely to be observed in ontogenetically older
<taxonomicName id="4C4182F9FFE70E50FFBE528AFF13F989" authorityName="Osborn" authorityYear="1905" box="[96,155,1513,1536]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="4" pageNumber="5" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE70E50FFBE528AFF13F989" box="[96,155,1513,1536]" italics="true" pageId="4" pageNumber="5">T. rex</emphasis>
</taxonomicName>
individuals. To test this hypothesis, we examined femur and tibia thin sections from
<taxonomicName id="4C4182F9FFE70E50FEBC5165FE28F994" authorityName="Osborn" authorityYear="1905" box="[354,416,1542,1565]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="4" pageNumber="5" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE70E50FEBC5165FE28F994" box="[354,416,1542,1565]" italics="true" pageId="4" pageNumber="5">T. rex</emphasis>
</taxonomicName>
specimens
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,
<materialsCitation id="3B29F327FFE70E50FE0C5140FF1BF9D1" ID-GBIF-Occurrence="3396425365" collectionCode="MOR" pageId="4" pageNumber="5" specimenCode="MOR 1125">MOR (Museum of the Rockies) 1125</materialsCitation>
,
<materialsCitation id="3B29F327FFE70E50FF435123FE98F9D1" ID-GBIF-Occurrence="3396425302" box="[157,272,1600,1624]" collectionCode="MOR" pageId="4" pageNumber="5" specimenCode="MOR 1128">MOR 1128</materialsCitation>
,
<materialsCitation id="3B29F327FFE70E50FEC75123FE04F9D1" ID-GBIF-Occurrence="3396425319" box="[281,396,1600,1624]" collectionCode="MOR" pageId="4" pageNumber="5" specimenCode="MOR 1198">MOR 1198</materialsCitation>
, and
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. In all individuals, variability in annual zonal thicknesses was observed. In particular, compared to zone spacing within the mid-cortex, noticeably thinner zones are present within the innermost cortex of
<materialsCitation id="3B29F327FFE70E50FF2E51D6FE3AF944" ID-GBIF-Occurrence="3396425391" box="[240,434,1717,1742]" collectionCode="USNM" httpUri="http://n2t.net/ark:/65665/381d4ee9c-91b4-4ce0-89eb-9053746a9351" pageId="4" pageNumber="5" specimenCode="USNM PAL 555000">USNM PAL 555000</materialsCitation>
(
<figureCitation id="137AE5FFFFE70E50FE6351D6FD8DF944" box="[445,517,1717,1741]" captionStart="Fig" captionStartId="4.[808,838,1591,1611]" captionTargetBox="[813,1484,161,1574]" captionTargetId="figure@4.[812,1484,160,1575]" captionTargetPageId="4" captionText="Fig. 4. Examples of variable CGM (blue lines) spacing in tyrannosaurids examined for this study. (A) The variability of CGM spacing in the femur of BMRP 2002.4.1 and (B) the tibia of BMRP 2006.4.4 may imply that these individuals were approaching asymptotic body length. Howeverι CGMs within the innermost cortices of much larger T.rex specimens (C) USNM PAL 555000 and (D) MOR 1128 demonstrate that the CGM spacing is not a reliable indicator of relative maturity status.All panels are shown in transverse thin section." figureDoi="http://doi.org/10.5281/zenodo.3749032" httpUri="https://zenodo.org/record/3749032/files/figure.png" pageId="4" pageNumber="5">Fig. 4C</figureCitation>
) and
<materialsCitation id="3B29F327FFE70E50FDE451D6FD2EF944" ID-GBIF-Occurrence="3396425369" box="[570,678,1717,1741]" collectionCode="MOR" pageId="4" pageNumber="5" specimenCode="MOR 1128">MOR 1128</materialsCitation>
(
<figureCitation id="137AE5FFFFE70E50FD6C51D6FD75F944" box="[690,765,1717,1741]" captionStart="Fig" captionStartId="4.[808,838,1591,1611]" captionTargetBox="[813,1484,161,1574]" captionTargetId="figure@4.[812,1484,160,1575]" captionTargetPageId="4" captionText="Fig. 4. Examples of variable CGM (blue lines) spacing in tyrannosaurids examined for this study. (A) The variability of CGM spacing in the femur of BMRP 2002.4.1 and (B) the tibia of BMRP 2006.4.4 may imply that these individuals were approaching asymptotic body length. Howeverι CGMs within the innermost cortices of much larger T.rex specimens (C) USNM PAL 555000 and (D) MOR 1128 demonstrate that the CGM spacing is not a reliable indicator of relative maturity status.All panels are shown in transverse thin section." figureDoi="http://doi.org/10.5281/zenodo.3749032" httpUri="https://zenodo.org/record/3749032/files/figure.png" pageId="4" pageNumber="5">Fig. 4D</figureCitation>
). These results contradict the mathematically predictable zonal spacing in
<taxonomicName id="4C4182F9FFE70E50FFA45192FF3BF881" authorityName="Osborn" authorityYear="1905" box="[122,179,1777,1800]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="4" pageNumber="5" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE70E50FFA45192FF3BF881" box="[122,179,1777,1800]" italics="true" pageId="4" pageNumber="5">T. rex</emphasis>
</taxonomicName>
long bones reported by Horner and Padian (
<bibRefCitation id="EFD0848BFFE70E50FDA85193FD0AF88E" author="J. R. Horner &amp; K. Padian" box="[630,642,1776,1799]" journalOrPublisher="Proc. R. soc. Lond. B Biol. sci." pageId="4" pageNumber="5" pagination="1875 - 1880" part="271" refId="ref7285" refString="5. J. R. Horner, K. Padian, Age and growth dynamics of Tyrannosaurus rex. Proc. R. soc. Lond. B Biol. sci. 271, 1875 - 1880 (2004)." title="Age and growth dynamics of Tyrannosaurus rex" type="journal article" year="2004">
<emphasis id="B9352568FFE70E50FDA85193FD0AF88E" box="[630,642,1776,1799]" italics="true" pageId="4" pageNumber="5">5</emphasis>
</bibRefCitation>
), which used some of the same specimens reassessed in the present study. Results further suggest not only that
<materialsCitation id="3B29F327FFE70E50FE4F5048FDBAF8CA" ID-GBIF-Occurrence="3396425415" box="[401,562,1835,1859]" collectionCode="BMRP" pageId="4" pageNumber="5" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
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had not yet entered the accelerated growth period proposed for this taxon (
<bibRefCitation id="EFD0848BFFE70E50FCAE506DFCF4F8AF" author="G. M. Erickson &amp; P. J. Makovicky &amp; P. J. Currie &amp; M. A. Norell &amp; S. A. Yerby &amp; C. A. Brochu" box="[880,892,1806,1830]" journalOrPublisher="Nature" pageId="4" pageNumber="5" pagination="772 - 775" part="430" refId="ref7228" refString="4. G. M. Erickson, P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, C. A. Brochu, Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature 430, 772 - 775 (2004)." title="Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs" type="journal article" year="2004">
<emphasis id="B9352568FFE70E50FCAE506DFCF4F8AF" box="[880,892,1806,1830]" italics="true" pageId="4" pageNumber="5">4</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE70E50FC59506DFC1BF8AC" author="J. R. Horner &amp; K. Padian" box="[903,915,1806,1829]" journalOrPublisher="Proc. R. soc. Lond. B Biol. sci." pageId="4" pageNumber="5" pagination="1875 - 1880" part="271" refId="ref7285" refString="5. J. R. Horner, K. Padian, Age and growth dynamics of Tyrannosaurus rex. Proc. R. soc. Lond. B Biol. sci. 271, 1875 - 1880 (2004)." title="Age and growth dynamics of Tyrannosaurus rex" type="journal article" year="2004">
<emphasis id="B9352568FFE70E50FC59506DFC1BF8AC" box="[903,915,1806,1829]" italics="true" pageId="4" pageNumber="5">5</emphasis>
</bibRefCitation>
) but also that the accuracy of the generalized
<taxonomicName id="4C4182F9FFE70E50FA80506DFA10F8AC" authorityName="Osborn" authorityYear="1905" box="[1374,1432,1806,1829]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="4" pageNumber="5" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE70E50FA80506DFA10F8AC" box="[1374,1432,1806,1829]" italics="true" pageId="4" pageNumber="5">T. rex</emphasis>
</taxonomicName>
body mass curve from Erickson
<emphasis id="B9352568FFE70E50FBEA504FFBECF8CA" box="[1076,1124,1835,1859]" italics="true" pageId="4" pageNumber="5">et al.</emphasis>
(
<bibRefCitation id="EFD0848BFFE70E50FBAC5048FBF6F8CA" author="G. M. Erickson &amp; P. J. Makovicky &amp; P. J. Currie &amp; M. A. Norell &amp; S. A. Yerby &amp; C. A. Brochu" box="[1138,1150,1835,1859]" journalOrPublisher="Nature" pageId="4" pageNumber="5" pagination="772 - 775" part="430" refId="ref7228" refString="4. G. M. Erickson, P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, C. A. Brochu, Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature 430, 772 - 775 (2004)." title="Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs" type="journal article" year="2004">
<emphasis id="B9352568FFE70E50FBAC5048FBF6F8CA" box="[1138,1150,1835,1859]" italics="true" pageId="4" pageNumber="5">4</emphasis>
</bibRefCitation>
) would be affected by undetected individual variation in annual growth.
</paragraph>
<caption id="DF3EA9F2FFE70E50FCF65154FB1CF965" ID-DOI="http://doi.org/10.5281/zenodo.3749032" ID-Zenodo-Dep="3749032" httpUri="https://zenodo.org/record/3749032/files/figure.png" pageId="4" pageNumber="5" startId="4.[808,838,1591,1611]" targetBox="[813,1484,161,1574]" targetPageId="4">
<paragraph id="8BFEF97AFFE70E50FCF65154FB1CF965" blockId="4.[808,1488,1591,1772]" pageId="4" pageNumber="5">
<emphasis id="B9352568FFE70E50FCF65154FC53F9EC" bold="true" pageId="4" pageNumber="5">Fig. 4. Examples of variable CGM (blue lines) spacing in tyrannosaurids examined for this study.</emphasis>
(
<emphasis id="B9352568FFE70E50FC385132FC7BF9EC" bold="true" box="[998,1011,1617,1637]" pageId="4" pageNumber="5">A</emphasis>
) The variability of CGM spacing in the femur of
<materialsCitation id="3B29F327FFE70E50FA415131FCE6F908" ID-GBIF-Occurrence="3396425375" collectionCode="BMRP" pageId="4" pageNumber="5" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and (
<emphasis id="B9352568FFE70E50FC43510FFC21F909" bold="true" box="[925,937,1644,1664]" pageId="4" pageNumber="5">B</emphasis>
) the tibia of
<materialsCitation id="3B29F327FFE70E50FBCD510EFB06F908" ID-GBIF-Occurrence="3396425358" box="[1043,1166,1645,1665]" collectionCode="BMRP" pageId="4" pageNumber="5" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
may imply that these individuals were approaching asymptotic body length. However, CGMs within the innermost cortices of much larger
<taxonomicName id="4C4182F9FFE70E50FC7951C2FC59F93C" authorityName="Osborn" authorityYear="1905" box="[935,977,1697,1717]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="4" pageNumber="5" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE70E50FC7951C2FC59F93C" box="[935,977,1697,1717]" italics="true" pageId="4" pageNumber="5">T.rex</emphasis>
</taxonomicName>
specimens (
<emphasis id="B9352568FFE70E50FBE751C2FBCDF93C" bold="true" box="[1081,1093,1697,1717]" pageId="4" pageNumber="5">C</emphasis>
)
<materialsCitation id="3B29F327FFE70E50FB8E51C1FB64F93F" ID-GBIF-Occurrence="3396425384" box="[1104,1260,1698,1718]" collectionCode="USNM" httpUri="http://n2t.net/ark:/65665/381d4ee9c-91b4-4ce0-89eb-9053746a9351" pageId="4" pageNumber="5" specimenCode="USNM PAL 555000">USNM PAL 555000</materialsCitation>
and (
<emphasis id="B9352568FFE70E50FAC451C2FAA0F93C" bold="true" box="[1306,1320,1697,1717]" pageId="4" pageNumber="5">D</emphasis>
)
<materialsCitation id="3B29F327FFE70E50FAED51C1FA01F93F" ID-GBIF-Occurrence="3396425399" box="[1331,1417,1698,1718]" collectionCode="MOR" pageId="4" pageNumber="5" specimenCode="MOR 1128">MOR 1128</materialsCitation>
demonstrate that the CGM spacing is not a reliable indicator of relative maturity status.All panels are shown in transverse thin section.
</paragraph>
</caption>
<paragraph id="8BFEF97AFFE60E51FF5E57C1FE47FD43" blockId="5.[96,776,162,715]" pageId="5" pageNumber="6">
Variable LAG spacing is reported in ornithomimids, ornithopods [(
<bibRefCitation id="EFD0848BFFE60E51FFAF57A3FF00FF51" author="T. M. Cullen &amp; D. C. Evans &amp; M. J. Ryan &amp; P. J. Currie &amp; Y. Kobayashi" box="[113,136,192,216]" journalOrPublisher="BMC Evol. Biol." pageId="5" pageNumber="6" pagination="231" part="14" refId="ref7906" refString="19. T. M. Cullen, D. C. Evans, M. J. Ryan, P. J. Currie, Y. Kobayashi, Osteohistological variation in growth marks and osteocyte lacunar density in a theropod dinosaur (Coelurosauria: Ornithomimidae). BMC Evol. Biol. 14, 231 (2014)." title="Osteohistological variation in growth marks and osteocyte lacunar density in a theropod dinosaur (Coelurosauria: Ornithomimidae)" type="journal article" year="2014">
<emphasis id="B9352568FFE60E51FFAF57A3FF00FF51" box="[113,136,192,216]" italics="true" pageId="5" pageNumber="6">19</emphasis>
</bibRefCitation>
) and references therein], and other tyrannosauroids (
<bibRefCitation id="EFD0848BFFE60E51FD5157A3FD2EFF51" author="L. E. Zanno &amp; R. T. Tucker &amp; A. Canoville &amp; H. M. Avrahami &amp; T. A. Gates &amp; P. J. Makovicky" box="[655,678,192,216]" journalOrPublisher="Commun. Biol." pageId="5" pageNumber="6" pagination="64" part="2" refId="ref7736" refString="15. L. E. Zanno, R. T. Tucker, A. Canoville, H. M. Avrahami, T. A. Gates, P. J. Makovicky, Diminutive fleet-footed tyrannosauroid narrows the 70 - million-year gap in the North American fossil record. Commun. Biol. 2, 64 (2019)." title="Diminutive fleet-footed tyrannosauroid narrows the 70 - million-year gap in the North American fossil record" type="journal article" year="2019">
<emphasis id="B9352568FFE60E51FD5157A3FD2EFF51" box="[655,678,192,216]" italics="true" pageId="5" pageNumber="6">15</emphasis>
</bibRefCitation>
) and may correlate with annual resource abundance (
<bibRefCitation id="EFD0848BFFE60E51FDCE57BEFDA0FF7C" author="M. Kohler &amp; N. Marin-Moratalla &amp; X. Jordana &amp; R. Aanes" box="[528,552,221,245]" journalOrPublisher="Nature" pageId="5" pageNumber="6" pagination="358 - 361" part="487" refId="ref7590" refString="12. M. Kohler, N. Marin-Moratalla, X. Jordana, R. Aanes, Seasonal bone growth and physiology in endotherms shed light on dinosaur physiology. Nature 487, 358 - 361 (2012)." title="Seasonal bone growth and physiology in endotherms shed light on dinosaur physiology" type="journal article" year="2012">
<emphasis id="B9352568FFE60E51FDCE57BEFDA0FF7C" box="[528,552,221,245]" italics="true" pageId="5" pageNumber="6">12</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE60E51FDEA57BEFDC4FF7C" author="T. M. Cullen &amp; D. C. Evans &amp; M. J. Ryan &amp; P. J. Currie &amp; Y. Kobayashi" box="[564,588,221,245]" journalOrPublisher="BMC Evol. Biol." pageId="5" pageNumber="6" pagination="231" part="14" refId="ref7906" refString="19. T. M. Cullen, D. C. Evans, M. J. Ryan, P. J. Currie, Y. Kobayashi, Osteohistological variation in growth marks and osteocyte lacunar density in a theropod dinosaur (Coelurosauria: Ornithomimidae). BMC Evol. Biol. 14, 231 (2014)." title="Osteohistological variation in growth marks and osteocyte lacunar density in a theropod dinosaur (Coelurosauria: Ornithomimidae)" type="journal article" year="2014">
<emphasis id="B9352568FFE60E51FDEA57BEFDC4FF7C" box="[564,588,221,245]" italics="true" pageId="5" pageNumber="6">19</emphasis>
</bibRefCitation>
). Our data suggest that this trait also characterizes
<taxonomicName id="4C4182F9FFE60E51FE4B5798FE45FE9B" authorityName="Osborn" authorityYear="1905" box="[405,461,251,274]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FE4B5798FE45FE9B" box="[405,461,251,274]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
: Because the level of bone tissue organization within zones remained the same from the innermost cortex to the periosteal surface in the BMRP specimens, growth rates were within a similar range from year to year. To produce these extremes in annual bone apposition, the duration of the growth hiatus must have varied annually. On the basis of the larger
<taxonomicName id="4C4182F9FFE60E51FDBA56EDFD14FE2C" authorityName="Osborn" authorityYear="1905" box="[612,668,398,421]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FDBA56EDFD14FE2C" box="[612,668,398,421]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
specimens examined here for comparison, the adjustment of annual growth hiatus duration in response to resource abundance is a physiological characteristic observed throughout
<taxonomicName id="4C4182F9FFE60E51FE6E5685FE6DFE74" authorityName="Osborn" authorityYear="1905" box="[432,485,486,509]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FE6E5685FE6DFE74" box="[432,485,486,509]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
ontogeny. Regardless of cause, unpredictable CGM spacing observed here and in previous studies stresses caution when inferring relative maturity based on cortical LAG spacing (
<bibRefCitation id="EFD0848BFFE60E51FF2A555EFE84FDDC" author="T. M. Cullen &amp; D. C. Evans &amp; M. J. Ryan &amp; P. J. Currie &amp; Y. Kobayashi" box="[244,268,573,597]" journalOrPublisher="BMC Evol. Biol." pageId="5" pageNumber="6" pagination="231" part="14" refId="ref7906" refString="19. T. M. Cullen, D. C. Evans, M. J. Ryan, P. J. Currie, Y. Kobayashi, Osteohistological variation in growth marks and osteocyte lacunar density in a theropod dinosaur (Coelurosauria: Ornithomimidae). BMC Evol. Biol. 14, 231 (2014)." title="Osteohistological variation in growth marks and osteocyte lacunar density in a theropod dinosaur (Coelurosauria: Ornithomimidae)" type="journal article" year="2014">
<emphasis id="B9352568FFE60E51FF2A555EFE84FDDC" box="[244,268,573,597]" italics="true" pageId="5" pageNumber="6">19</emphasis>
</bibRefCitation>
). The observation of closely spaced CGMs within the innermost cortices of larger
<taxonomicName id="4C4182F9FFE60E51FE725538FE6FFDFB" authorityName="Osborn" authorityYear="1905" box="[428,487,603,626]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FE725538FE6FFDFB" box="[428,487,603,626]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
validates our interpretation that the thin zonal spacing observed in the outermost cortices of
<materialsCitation id="3B29F327FFE60E51FFBE55F5FF70FD24" ID-GBIF-Occurrence="3396425371" box="[96,248,661,685]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
<materialsCitation id="3B29F327FFE60E51FEF655F5FE48FD24" ID-GBIF-Occurrence="3396425329" box="[296,448,661,685]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
are not reliable indicators of relative maturity when an EFS is absent.
</paragraph>
<paragraph id="8BFEF97AFFE60E51FFBE558FFDD6FC8C" blockId="5.[96,776,748,1888]" box="[96,606,748,774]" pageId="5" pageNumber="6">
<emphasis id="B9352568FFE60E51FFBE558FFDD6FC8C" bold="true" box="[96,606,748,774]" pageId="5" pageNumber="6">
Implications for the
<taxonomicName id="4C4182F9FFE60E51FE9E558EFE55FC8F" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[320,477,749,774]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FE9E558EFE55FC8F" bold="true" box="[320,477,749,774]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
hypothesis
</emphasis>
</paragraph>
<paragraph id="8BFEF97AFFE60E51FFBE5468FA8DFE74" blockId="5.[96,776,748,1888]" lastBlockId="5.[808,1488,163,509]" pageId="5" pageNumber="6">
The bone microstructural interpretations discussed here not only provide insight into
<taxonomicName id="4C4182F9FFE60E51FF0B544AFE85FCC9" authorityName="Osborn" authorityYear="1905" box="[213,269,809,832]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FF0B544AFE85FCC9" box="[213,269,809,832]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
ontogeny but also have bearing on discussions concerning
<materialsCitation id="3B29F327FFE60E51FF6C5426FD53FCD4" ID-GBIF-Occurrence="3396425417" box="[178,731,837,861]" collectionCode="CMNH" pageId="5" pageNumber="6" specimenCode="CMNH 7541">CMNH (Cleveland Museum of Natural History) 7541</materialsCitation>
and
<taxonomicName id="4C4182F9FFE60E51FFBE5400FF65FCF3" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[96,237,867,890]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FFBE5400FF65FCF3" box="[96,237,867,890]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
.
<materialsCitation id="3B29F327FFE60E51FF295400FEF0FCF3" ID-GBIF-Occurrence="3396425380" box="[247,376,866,891]" collectionCode="CMNH" pageId="5" pageNumber="6" specimenCode="CMNH 7541">CMNH 7541</materialsCitation>
consists of a small isolated skull 572 mm in length (
<bibRefCitation id="EFD0848BFFE60E51FF1754E3FF69FC11" author="T. D. Carr" box="[201,225,896,920]" journalOrPublisher="J. Vertebr. Paleontol." pageId="5" pageNumber="6" pagination="497 - 520" part="19" refId="ref7967" refString="20. T. D. Carr, Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria). J. Vertebr. Paleontol. 19, 497 - 520 (1999)." title="Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria)" type="journal article" year="1999">
<emphasis id="B9352568FFE60E51FF1754E3FF69FC11" box="[201,225,896,920]" italics="true" pageId="5" pageNumber="6">20</emphasis>
</bibRefCitation>
). Inferred to be sympatric with
<taxonomicName id="4C4182F9FFE60E51FDFC54E2FDD4FC11" authorityName="Osborn" authorityYear="1905" box="[546,604,897,920]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FDFC54E2FDD4FC11" box="[546,604,897,920]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
, it was originally named
<taxonomicName id="4C4182F9FFE60E51FF7954FDFEFAFC3C" baseAuthorityName="Gilmore" baseAuthorityYear="1946" box="[167,370,925,949]" class="Reptilia" family="Tyrannosauridae" genus="Gorgosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="lancensis">
<emphasis id="B9352568FFE60E51FF7954FDFEFAFC3C" box="[167,370,925,949]" italics="true" pageId="5" pageNumber="6">Gorgosaurus lancensis</emphasis>
</taxonomicName>
(
<bibRefCitation id="EFD0848BFFE60E51FEA154FEFE1DFC3C" author="C. W. Gilmore" box="[383,405,925,949]" journalOrPublisher="smithson. misc. collect." pageId="5" pageNumber="6" pagination="1 - 19" part="106" refId="ref8000" refString="21. C. W. Gilmore, New carnivorous dinosaur from the Lance formation of Montana. smithson. misc. collect. 106, 1 - 19 (1946)." title="New carnivorous dinosaur from the Lance formation of Montana" type="journal article" year="1946">
<emphasis id="B9352568FFE60E51FEA154FEFE1DFC3C" box="[383,405,925,949]" italics="true" pageId="5" pageNumber="6">21</emphasis>
</bibRefCitation>
). In 1988, Bakker
<emphasis id="B9352568FFE60E51FD9E54FDFDE4FC3C" box="[576,620,925,949]" italics="true" pageId="5" pageNumber="6">et al.</emphasis>
(
<bibRefCitation id="EFD0848BFFE60E51FDA654FEFD06FC3C" author="R. T. Bakker &amp; M. Williams &amp; P. J. Currie" box="[632,654,925,949]" journalOrPublisher="Hunteria" pageId="5" pageNumber="6" pagination="1 - 30" part="1" refId="ref8033" refString="22. R. T. Bakker, M. Williams, P. J. Currie, Nanotyrannus, a new genus of pygmy tyrannosaur, from the latest Cretaceous of Montana. Hunteria 1, 1 - 30 (1988)." title="Nanotyrannus, a new genus of pygmy tyrannosaur, from the latest Cretaceous of Montana" type="journal article" year="1988">
<emphasis id="B9352568FFE60E51FDA654FEFD06FC3C" box="[632,654,925,949]" italics="true" pageId="5" pageNumber="6">22</emphasis>
</bibRefCitation>
) redescribed
<materialsCitation id="3B29F327FFE60E51FFBE54D8FF6EFC5B" ID-GBIF-Occurrence="3396425382" box="[96,230,954,979]" collectionCode="CMNH" pageId="5" pageNumber="6" specimenCode="CMNH 7541">CMNH 7541</materialsCitation>
as an adult specimen of a new genus,
<taxonomicName id="4C4182F9FFE60E51FDAF54D8FC8AFC5B" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[625,770,955,978]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FDAF54D8FC8AFC5B" box="[625,770,955,978]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
. Using an extensive empirical dataset, Carr and Williamson (
<bibRefCitation id="EFD0848BFFE60E51FD4A54BBFD23FC79" author="T. D. Carr &amp; T. E. Williamson" box="[660,683,984,1008]" journalOrPublisher="Zool. J. Linnean soc." pageId="5" pageNumber="6" pagination="419 - 523" part="142" refId="ref8077" refString="23. T. D. Carr, T. E. Williamson, Diversity of Late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America. Zool. J. Linnean soc. 142, 419 - 523 (2004)." title="Diversity of Late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America" type="journal article" year="2004">
<emphasis id="B9352568FFE60E51FD4A54BBFD23FC79" box="[660,683,984,1008]" italics="true" pageId="5" pageNumber="6">23</emphasis>
</bibRefCitation>
) formally synonymized
<taxonomicName id="4C4182F9FFE60E51FF345495FEFFFB84" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[234,375,1014,1037]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FF345495FEFFFB84" box="[234,375,1014,1037]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
into
<taxonomicName id="4C4182F9FFE60E51FE725495FDC8FB84" authorityName="Osborn" authorityYear="1905" box="[428,576,1014,1037]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FE725495FDC8FB84" box="[428,576,1014,1037]" italics="true" pageId="5" pageNumber="6">Tyrannosaurus</emphasis>
</taxonomicName>
in 2004, supporting the interpretation of
<materialsCitation id="3B29F327FFE60E51FEE95370FE34FBA3" ID-GBIF-Occurrence="3396425379" box="[311,444,1042,1067]" collectionCode="CMNH" pageId="5" pageNumber="6" specimenCode="CMNH 7541">CMNH 7541</materialsCitation>
as a juvenile
<taxonomicName id="4C4182F9FFE60E51FD995370FD0AFBA3" authorityName="Osborn" authorityYear="1905" box="[583,642,1043,1066]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FD995370FD0AFBA3" box="[583,642,1043,1066]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
proposed by Rozhdestvensky in 1965 (
<bibRefCitation id="EFD0848BFFE60E51FE895353FEE6FBC1" author="A. K. Rozhdestvensky" box="[343,366,1072,1096]" journalOrPublisher="Paleontol. Zh." pageId="5" pageNumber="6" pagination="95 - 109" part="3" refId="ref8122" refString="24. A. K. Rozhdestvensky, Growth changes in Asian dinosaurs and some problems of their taxonomy. Paleontol. Zh. 3, 95 - 109 (1965)." title="Growth changes in Asian dinosaurs and some problems of their taxonomy" type="journal article" year="1965">
<emphasis id="B9352568FFE60E51FE895353FEE6FBC1" box="[343,366,1072,1096]" italics="true" pageId="5" pageNumber="6">24</emphasis>
</bibRefCitation>
). Presently, most tyrannosaurid specialists consider
<materialsCitation id="3B29F327FFE60E51FF64532EFEB4FBEC" ID-GBIF-Occurrence="3396425349" box="[186,316,1101,1125]" collectionCode="CMNH" pageId="5" pageNumber="6" specimenCode="CMNH 7541">CMNH 7541</materialsCitation>
and possible referred specimens to be juvenile
<taxonomicName id="4C4182F9FFE60E51FFBE5308FF17FB0B" authorityName="Osborn" authorityYear="1905" box="[96,159,1131,1154]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FFBE5308FF17FB0B" box="[96,159,1131,1154]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
based on morphological skull features shared with those found in undisputed juvenile individuals of other tyrannosaurid taxa [e.g., (
<bibRefCitation id="EFD0848BFFE60E51FF4053C6FF22FB34" author="S. L. Brusatte &amp; M. A. Norell &amp; T. D. Carr &amp; G. M. Erickson &amp; J. R. Hutchinson &amp; A. M. Balanoff &amp; G. S. Bever &amp; J. N. Choiniere &amp; P. J. Makovicky &amp; X. Xu" box="[158,170,1189,1213]" journalOrPublisher="science" pageId="5" pageNumber="6" pagination="1481 - 1485" part="329" refId="ref7118" refString="2. S. L. Brusatte, M. A. Norell, T. D. Carr, G. M. Erickson, J. R. Hutchinson, A. M. Balanoff, G. S. Bever, J. N. Choiniere, P. J. Makovicky, X. Xu, Tyrannosaur paleobiology: New research on ancient exemplar organisms. science 329, 1481 - 1485 (2010)." title="Tyrannosaur paleobiology: New research on ancient exemplar organisms" type="journal article" year="2010">
<emphasis id="B9352568FFE60E51FF4053C6FF22FB34" box="[158,170,1189,1213]" italics="true" pageId="5" pageNumber="6">2</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE60E51FF6B53C6FF44FB34" author="T. D. Carr" box="[181,204,1189,1213]" journalOrPublisher="J. Vertebr. Paleontol." pageId="5" pageNumber="6" pagination="497 - 520" part="19" refId="ref7967" refString="20. T. D. Carr, Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria). J. Vertebr. Paleontol. 19, 497 - 520 (1999)." title="Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria)" type="journal article" year="1999">
<emphasis id="B9352568FFE60E51FF6B53C6FF44FB34" box="[181,204,1189,1213]" italics="true" pageId="5" pageNumber="6">20</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE60E51FF0753C6FF78FB34" author="T. D. Carr &amp; T. E. Williamson" box="[217,240,1189,1213]" journalOrPublisher="Zool. J. Linnean soc." pageId="5" pageNumber="6" pagination="419 - 523" part="142" refId="ref8077" refString="23. T. D. Carr, T. E. Williamson, Diversity of Late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America. Zool. J. Linnean soc. 142, 419 - 523 (2004)." title="Diversity of Late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America" type="journal article" year="2004">
<emphasis id="B9352568FFE60E51FF0753C6FF78FB34" box="[217,240,1189,1213]" italics="true" pageId="5" pageNumber="6">23</emphasis>
</bibRefCitation>
,
<emphasis id="B9352568FFE60E51FF2253C6FEB0FB34" box="[252,312,1189,1213]" italics="true" pageId="5" pageNumber="6">
<bibRefCitation id="EFD0848BFFE60E51FF2253C6FE9BFB34" author="C. A. Brochu" box="[252,275,1189,1213]" journalOrPublisher="J. Vertebr. Paleontol. Memoir" pageId="5" pageNumber="6" pagination="1 - 138" part="22" refId="ref8155" refString="25. C. A. Brochu, Osteology of Tyrannosaurus rex: Insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull. J. Vertebr. Paleontol. Memoir 22, 1 - 138 (2003)." title="Osteology of Tyrannosaurus rex: Insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull" type="journal article" year="2003">25</bibRefCitation>
–
<bibRefCitation id="EFD0848BFFE60E51FEFF53C6FEB0FB34" author="T. R. Holtz Jr." box="[289,312,1189,1213]" editor="D. Weishampel &amp; P. Dodson &amp; H. Osmolska" journalOrPublisher="University of California Press, Berkeley" pageId="5" pageNumber="6" pagination="111 - 136" refId="ref8336" refString="28. T. R. Holtz Jr., The Dinosauria, D. Weishampel, P. Dodson, H. Osmolska, Eds. (University of California Press, Berkeley, 2004), pp. 111 - 136." title="The Dinosauria" type="book chapter" year="2004">28</bibRefCitation>
</emphasis>
)]. Nonetheless, several publications have since argued for the validity of
<taxonomicName id="4C4182F9FFE60E51FE8053A0FE67FB53" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[350,495,1219,1242]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FE8053A0FE67FB53" box="[350,495,1219,1242]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
based not only on morphological characters of the
<materialsCitation id="3B29F327FFE60E51FE955383FE43FB71" ID-GBIF-Occurrence="3396425311" box="[331,459,1248,1272]" collectionCode="CMNH" pageId="5" pageNumber="6" specimenCode="CMNH 7541">CMNH 7541</materialsCitation>
type skull but also on characters from the somewhat larger skull of
<materialsCitation id="3B29F327FFE60E51FE73539DFDCCFA9C" ID-GBIF-Occurrence="3396425414" box="[429,580,1277,1301]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
(720 mm in length) [e.g., (
<emphasis id="B9352568FFE60E51FF455278FF5EFABA" box="[155,214,1307,1331]" italics="true" pageId="5" pageNumber="6">
<bibRefCitation id="EFD0848BFFE60E51FF455278FF3AFABA" author="T. Tsuihiji &amp; M. Watabe &amp; K. Tsogtbaatar &amp; T. Tsubamoto &amp; R. Barsbold &amp; S. Suzuki &amp; A. H. Lee &amp; R. C. Ridgely &amp; Y. Kawahara &amp; L. M. Witmer" box="[155,178,1307,1331]" journalOrPublisher="J. Vertebr. Paleontol." pageId="5" pageNumber="6" pagination="497 - 517" part="31" refId="ref8380" refString="29. T. Tsuihiji, M. Watabe, K. Tsogtbaatar, T. Tsubamoto, R. Barsbold, S. Suzuki, A. H. Lee, R. C. Ridgely, Y. Kawahara, L. M. Witmer, Cranial osteology of a juvenile specimen of Tarbosaurus bataar from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia. J. Vertebr. Paleontol. 31, 497 - 517 (2011)." title="Cranial osteology of a juvenile specimen of Tarbosaurus bataar from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia" type="journal article" year="2011">29</bibRefCitation>
–
<bibRefCitation id="EFD0848BFFE60E51FF615278FF5EFABA" author="L. M. Witmer &amp; R. C. Ridgely" box="[191,214,1307,1331]" journalOrPublisher="Kirtlandia" pageId="5" pageNumber="6" pagination="61 - 81" part="57" refId="ref8616" refString="33. L. M. Witmer, R. C. Ridgely, The Cleveland tyrannosaur skull (Nanotyrannus or Tyrannosaurus): new findings based on CT scanning, with special reference to the braincase. Kirtlandia 57, 61 - 81 (2010)." title="The Cleveland tyrannosaur skull (Nanotyrannus or Tyrannosaurus): new findings based on CT scanning, with special reference to the braincase" type="journal article" year="2010">33</bibRefCitation>
</emphasis>
)], which some researchers have assigned to
<taxonomicName id="4C4182F9FFE60E51FDA25278FC8FFABB" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[636,775,1307,1330]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FDA25278FC8FFABB" box="[636,775,1307,1330]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
based on shared morphological characters they consider adult autapomorphies of the taxon [e.g., (
<emphasis id="B9352568FFE60E51FE7E5236FE56FAE4" box="[416,478,1365,1389]" italics="true" pageId="5" pageNumber="6">
<bibRefCitation id="EFD0848BFFE60E51FE7E5236FE30FAE4" author="T. Tsuihiji &amp; M. Watabe &amp; K. Tsogtbaatar &amp; T. Tsubamoto &amp; R. Barsbold &amp; S. Suzuki &amp; A. H. Lee &amp; R. C. Ridgely &amp; Y. Kawahara &amp; L. M. Witmer" box="[416,440,1365,1389]" journalOrPublisher="J. Vertebr. Paleontol." pageId="5" pageNumber="6" pagination="497 - 517" part="31" refId="ref8380" refString="29. T. Tsuihiji, M. Watabe, K. Tsogtbaatar, T. Tsubamoto, R. Barsbold, S. Suzuki, A. H. Lee, R. C. Ridgely, Y. Kawahara, L. M. Witmer, Cranial osteology of a juvenile specimen of Tarbosaurus bataar from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia. J. Vertebr. Paleontol. 31, 497 - 517 (2011)." title="Cranial osteology of a juvenile specimen of Tarbosaurus bataar from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia" type="journal article" year="2011">29</bibRefCitation>
–
<bibRefCitation id="EFD0848BFFE60E51FE185236FE56FAE4" author="L. M. Witmer &amp; R. C. Ridgely" box="[454,478,1365,1389]" journalOrPublisher="Kirtlandia" pageId="5" pageNumber="6" pagination="61 - 81" part="57" refId="ref8616" refString="33. L. M. Witmer, R. C. Ridgely, The Cleveland tyrannosaur skull (Nanotyrannus or Tyrannosaurus): new findings based on CT scanning, with special reference to the braincase. Kirtlandia 57, 61 - 81 (2010)." title="The Cleveland tyrannosaur skull (Nanotyrannus or Tyrannosaurus): new findings based on CT scanning, with special reference to the braincase" type="journal article" year="2010">33</bibRefCitation>
</emphasis>
)]. Currently,
<materialsCitation id="3B29F327FFE60E51FDB45235FC80FAE4" ID-GBIF-Occurrence="3396425408" box="[618,776,1365,1389]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
is the only accessioned specimen with postcranial skeletal elements preserved that is specifically argued by proponents of
<taxonomicName id="4C4182F9FFE60E51FDA452F2FC80FA21" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[634,776,1425,1448]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FDA452F2FC80FA21" box="[634,776,1425,1448]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
as belonging to that genus [e.g., (
<emphasis id="B9352568FFE60E51FE7D52CEFE68FA4C" box="[419,480,1453,1477]" italics="true" pageId="5" pageNumber="6">
<bibRefCitation id="EFD0848BFFE60E51FE7D52CEFE33FA4C" author="T. Tsuihiji &amp; M. Watabe &amp; K. Tsogtbaatar &amp; T. Tsubamoto &amp; R. Barsbold &amp; S. Suzuki &amp; A. H. Lee &amp; R. C. Ridgely &amp; Y. Kawahara &amp; L. M. Witmer" box="[419,443,1453,1477]" journalOrPublisher="J. Vertebr. Paleontol." pageId="5" pageNumber="6" pagination="497 - 517" part="31" refId="ref8380" refString="29. T. Tsuihiji, M. Watabe, K. Tsogtbaatar, T. Tsubamoto, R. Barsbold, S. Suzuki, A. H. Lee, R. C. Ridgely, Y. Kawahara, L. M. Witmer, Cranial osteology of a juvenile specimen of Tarbosaurus bataar from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia. J. Vertebr. Paleontol. 31, 497 - 517 (2011)." title="Cranial osteology of a juvenile specimen of Tarbosaurus bataar from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia" type="journal article" year="2011">29</bibRefCitation>
–
<bibRefCitation id="EFD0848BFFE60E51FE1652CEFE68FA4C" author="N. L. Larson" box="[456,480,1453,1477]" editor="P. Larson &amp; K. Carpenter" journalOrPublisher="Indiana Univ. Press, Bloomington" pageId="5" pageNumber="6" pagination="1 - 56" refId="ref8573" refString="32. N. L. Larson, in Tyrannosaurus rex, the Tyrant King, P. Larson, K. Carpenter, Eds. (Indiana Univ. Press, Bloomington, 2008), pp. 1 - 56." type="book chapter" volumeTitle="Tyrannosaurus rex, the Tyrant King" year="2008">32</bibRefCitation>
</emphasis>
)]. Because
<materialsCitation id="3B29F327FFE60E51FD8E52CEFD5AFA4C" ID-GBIF-Occurrence="3396425422" box="[592,722,1453,1477]" collectionCode="CMNH" pageId="5" pageNumber="6" specimenCode="CMNH 7541">CMNH 7541</materialsCitation>
lacks the postcranial skeleton and proponents of
<taxonomicName id="4C4182F9FFE60E51FDDC52A8FD07FA6B" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[514,655,1483,1506]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FDDC52A8FD07FA6B" box="[514,655,1483,1506]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
refer
<materialsCitation id="3B29F327FFE60E51FD1852A8FF38F989" ID-GBIF-Occurrence="3396425416" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
to that taxon, the limb bone histology of
<materialsCitation id="3B29F327FFE60E51FDE0528BFD5DF989" ID-GBIF-Occurrence="3396425376" box="[574,725,1512,1536]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
(and additionally
<materialsCitation id="3B29F327FFE60E51FF065165FEF8F994" ID-GBIF-Occurrence="3396425419" box="[216,368,1541,1565]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
; see the Supplementary Materials for taxonomic discussion) reveals the life history of
<materialsCitation id="3B29F327FFE60E51FDC55140FD17F9B3" ID-GBIF-Occurrence="3396425310" box="[539,671,1570,1595]" collectionCode="CMNH" pageId="5" pageNumber="6" specimenCode="CMNH 7541">CMNH 7541</materialsCitation>
by proxy.
<subSubSection id="C35BAAF1FFE60E51FF5E5123FA8DFE74" pageId="5" pageNumber="6" type="discussion">
Here, we provide histological data that can be used to reject the hypothesis that
<taxonomicName id="4C4182F9FFE60E51FF23513DFE03F9FC" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[253,395,1630,1653]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FF23513DFE03F9FC" box="[253,395,1630,1653]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
was erected on the basis of a skeletally mature “pygmy” individual, resulting in two remaining alternative hypotheses: (i)
<taxonomicName id="4C4182F9FFE60E51FF2551FAFE04F939" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" box="[251,396,1689,1712]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FF2551FAFE04F939" box="[251,396,1689,1712]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
is a valid taxon, but the holotype and all currently referred specimens including
<materialsCitation id="3B29F327FFE60E51FE2351D5FD1DF944" ID-GBIF-Occurrence="3396425344" box="[509,661,1717,1741]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
<materialsCitation id="3B29F327FFE60E51FD1851D5FF3FF962" ID-GBIF-Occurrence="3396425343" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
are immature, with no skeletally mature individuals yet known; and (ii)
<materialsCitation id="3B29F327FFE60E51FEDD5193FE01F881" ID-GBIF-Occurrence="3396425338" box="[259,393,1776,1800]" collectionCode="CMNH" pageId="5" pageNumber="6" specimenCode="CMNH 7541">CMNH 7541</materialsCitation>
,
<materialsCitation id="3B29F327FFE60E51FE4C5193FDB9F881" ID-GBIF-Occurrence="3396425412" box="[402,561,1776,1800]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
,
<materialsCitation id="3B29F327FFE60E51FDE45193FD51F881" ID-GBIF-Occurrence="3396425313" box="[570,729,1776,1800]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, and other mid-sized tyrannosaurid specimens collected from the HCF represent juvenile ontogenetic stages of
<taxonomicName id="4C4182F9FFE60E51FE275048FDBCF8CB" authorityName="Osborn" authorityYear="1905" box="[505,564,1835,1858]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FE275048FDBCF8CB" box="[505,564,1835,1858]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
. Thus far, the femur and tibia of
<materialsCitation id="3B29F327FFE60E51FF08502BFEFAF8E9" ID-GBIF-Occurrence="3396425420" box="[214,370,1864,1888]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
<materialsCitation id="3B29F327FFE60E51FE7F502BFDB5F8E9" ID-GBIF-Occurrence="3396425351" box="[417,573,1864,1888]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
are the only weight-bearing bones of Upper Cretaceous HCF tyrannosaurids described histologically from complete transverse sections, and these universally demonstrate features characteristic of actively growing juvenile dinosaurs that had not yet entered an exponential phase of growth (as demonstrated by our new data identifying noticeably thinner zones within the innermost cortex of large-bodied
<taxonomicName id="4C4182F9FFE60E51FB315655FAA2FEC4" authorityName="Osborn" authorityYear="1905" box="[1263,1322,310,333]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FB315655FAA2FEC4" box="[1263,1322,310,333]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
specimens such as
<materialsCitation id="3B29F327FFE60E51FC9F5630FC74FEE3" ID-GBIF-Occurrence="3396425424" box="[833,1020,338,363]" collectionCode="USNM" httpUri="http://n2t.net/ark:/65665/381d4ee9c-91b4-4ce0-89eb-9053746a9351" pageId="5" pageNumber="6" specimenCode="USNM PAL 555000">USNM PAL 55500</materialsCitation>
). On the basis of these data, the latter hypothesis is most parsimonious and is congruent with the morphology-based conclusions of Carr (
<bibRefCitation id="EFD0848BFFE60E51FBDA56EEFB95FE2C" author="T. D. Carr" box="[1028,1053,397,421]" journalOrPublisher="J. Vertebr. Paleontol." pageId="5" pageNumber="6" pagination="497 - 520" part="19" refId="ref7967" refString="20. T. D. Carr, Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria). J. Vertebr. Paleontol. 19, 497 - 520 (1999)." title="Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria)" type="journal article" year="1999">
<emphasis id="B9352568FFE60E51FBDA56EEFB95FE2C" box="[1028,1053,397,421]" italics="true" pageId="5" pageNumber="6">20</emphasis>
</bibRefCitation>
) and Carr and Williamson (
<bibRefCitation id="EFD0848BFFE60E51FA9B56EEFAD6FE2C" author="T. D. Carr &amp; T. E. Williamson" box="[1349,1374,397,421]" journalOrPublisher="Zool. J. Linnean soc." pageId="5" pageNumber="6" pagination="419 - 523" part="142" refId="ref8077" refString="23. T. D. Carr, T. E. Williamson, Diversity of Late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America. Zool. J. Linnean soc. 142, 419 - 523 (2004)." title="Diversity of Late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America" type="journal article" year="2004">
<emphasis id="B9352568FFE60E51FA9B56EEFAD6FE2C" box="[1349,1374,397,421]" italics="true" pageId="5" pageNumber="6">23</emphasis>
</bibRefCitation>
). Incorporating additional mid-sized HCF tyrannosaurid specimens into this histology-based relative maturity assessment is necessary to further support or refute the parsimonious hypothesis.
</subSubSection>
</paragraph>
<subSubSection id="C35BAAF1FFE60E51FCF6557DFB61FDDC" pageId="5" pageNumber="6" type="reference_group">
<paragraph id="8BFEF97AFFE60E51FCF6557DFBE2FDBE" blockId="5.[808,1489,542,1477]" box="[808,1130,542,567]" pageId="5" pageNumber="6">
<heading id="D0B64E16FFE60E51FCF6557DFBE2FDBE" bold="true" box="[808,1130,542,567]" fontSize="10" level="3" pageId="5" pageNumber="6" reason="0">
<emphasis id="B9352568FFE60E51FCF6557DFBE2FDBE" bold="true" box="[808,1130,542,567]" pageId="5" pageNumber="6">Paleoecological implications</emphasis>
</heading>
</paragraph>
<paragraph id="8BFEF97AFFE60E51FCF6555EFB61FDDC" blockId="5.[808,1489,542,1477]" box="[808,1257,573,597]" pageId="5" pageNumber="6">
Synonymization of
<treatmentCitation id="0AE0DF6BFFE60E51FC34555DFBF0FDDC" authorityName="Bakker et al." authorityYear="1988" box="[1002,1144,574,597]" httpUri="http://treatment.plazi.org/id/03A1879D-FFD0-FFE9-5E7F-F664FEA6A618" pageId="5" pageNumber="6">
<taxonomicName id="4C4182F9FFE60E51FC34555DFBF0FDDC" authorityName="Bakker, Currie &amp; Williams" authorityYear="1988" baseAuthorityName="Gilmore" baseAuthorityYear="1946" box="[1002,1144,574,597]" class="Reptilia" family="Tyrannosauridae" genus="Nanotyrannus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="lancensis">
<emphasis id="B9352568FFE60E51FC34555DFBF0FDDC" box="[1002,1144,574,597]" italics="true" pageId="5" pageNumber="6">Nanotyrannus</emphasis>
</taxonomicName>
</treatmentCitation>
with
<taxonomicName id="4C4182F9FFE60E51FB6E555DFB61FDDC" authorityName="Osborn" authorityYear="1905" box="[1200,1257,574,597]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FB6E555DFB61FDDC" box="[1200,1257,574,597]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
</paragraph>
</subSubSection>
<subSubSection id="C35BAAF1FFE60E51FB30555DFA81FA4C" pageId="5" pageNumber="6" type="discussion">
<paragraph id="8BFEF97AFFE60E51FB30555DFA2FFB71" blockId="5.[808,1489,542,1477]" pageId="5" pageNumber="6">
means that rather than two sympatric tyrannosaurid taxa within faunal assemblages of the HCF, only one valid tyrannosaur species—
<taxonomicName id="4C4182F9FFE60E51FB02551AFA9FFD19" authorityName="Osborn" authorityYear="1905" box="[1244,1303,633,656]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FB02551AFA9FFD19" box="[1244,1303,633,656]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
—is currently recognized. As an adult,
<taxonomicName id="4C4182F9FFE60E51FC2155F5FBB0FD24" authorityName="Osborn" authorityYear="1905" box="[1023,1080,662,685]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FC2155F5FBB0FD24" box="[1023,1080,662,685]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
occupied the large-sized carnivore niche in the latest Cretaceous HCF ecosystem (
<bibRefCitation id="EFD0848BFFE60E51FB1055D0FB52FD42" author="S. L. Brusatte &amp; M. A. Norell &amp; T. D. Carr &amp; G. M. Erickson &amp; J. R. Hutchinson &amp; A. M. Balanoff &amp; G. S. Bever &amp; J. N. Choiniere &amp; P. J. Makovicky &amp; X. Xu" box="[1230,1242,691,715]" journalOrPublisher="science" pageId="5" pageNumber="6" pagination="1481 - 1485" part="329" refId="ref7118" refString="2. S. L. Brusatte, M. A. Norell, T. D. Carr, G. M. Erickson, J. R. Hutchinson, A. M. Balanoff, G. S. Bever, J. N. Choiniere, P. J. Makovicky, X. Xu, Tyrannosaur paleobiology: New research on ancient exemplar organisms. science 329, 1481 - 1485 (2010)." title="Tyrannosaur paleobiology: New research on ancient exemplar organisms" type="journal article" year="2010">
<emphasis id="B9352568FFE60E51FB1055D0FB52FD42" box="[1230,1242,691,715]" italics="true" pageId="5" pageNumber="6">2</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE60E51FB3955D0FB77FD42" author="J. R. Horner &amp; M. B. Goodwin &amp; N. Myhrvold" box="[1255,1279,691,715]" journalOrPublisher="PLOs ONE" pageId="5" pageNumber="6" pagination="e 16574" part="6" refId="ref8664" refString="34. J. R. Horner, M. B. Goodwin, N. Myhrvold, Dinosaur census reveals abundant Tyrannosaurus and rare ontogenetic stages in the Upper Cretaceous Hell Creek Formation (Maastrichtian), Montana, USA. PLOs ONE 6, e 16574 (2011)." title="Dinosaur census reveals abundant Tyrannosaurus and rare ontogenetic stages in the Upper Cretaceous Hell Creek Formation (Maastrichtian), Montana, USA" type="journal article" year="2011">
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), achieving an average adult body mass of ~9502 kg (
<bibRefCitation id="EFD0848BFFE60E51FB5755B3FB1DFD61" author="J. R. Hutchinson &amp; K. T. Bates &amp; J. Molnar &amp; V. Allen &amp; P. J. Makovicky" box="[1161,1173,720,744]" journalOrPublisher="PLOs ONE" pageId="5" pageNumber="6" pagination="e 26037" part="6" refId="ref7327" refString="6. J. R. Hutchinson, K. T. Bates, J. Molnar, V. Allen, P. J. Makovicky, A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth. PLOs ONE 6, e 26037 (2011)." title="A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth" type="journal article" year="2011">
<emphasis id="B9352568FFE60E51FB5755B3FB1DFD61" box="[1161,1173,720,744]" italics="true" pageId="5" pageNumber="6">6</emphasis>
</bibRefCitation>
) by 20 years of age (
<bibRefCitation id="EFD0848BFFE60E51FAB555B3FAFFFD61" author="G. M. Erickson &amp; P. J. Makovicky &amp; P. J. Currie &amp; M. A. Norell &amp; S. A. Yerby &amp; C. A. Brochu" box="[1387,1399,720,744]" journalOrPublisher="Nature" pageId="5" pageNumber="6" pagination="772 - 775" part="430" refId="ref7228" refString="4. G. M. Erickson, P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, C. A. Brochu, Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature 430, 772 - 775 (2004)." title="Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs" type="journal article" year="2004">
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</bibRefCitation>
).
<materialsCitation id="3B29F327FFE60E51FA5355B2FCF1FC8C" ID-GBIF-Occurrence="3396425383" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
<materialsCitation id="3B29F327FFE60E51FC76558DFBCAFC8C" ID-GBIF-Occurrence="3396425336" box="[936,1090,749,773]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, at&gt;13 and&gt;15 years of age, respectively, were only half the length of an adult
<taxonomicName id="4C4182F9FFE60E51FB405468FB50FCAB" authorityName="Osborn" authorityYear="1905" box="[1182,1240,779,802]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FB405468FB50FCAB" box="[1182,1240,779,802]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
(
<bibRefCitation id="EFD0848BFFE60E51FB395468FB7BFCAA" author="J. R. Hutchinson &amp; K. T. Bates &amp; J. Molnar &amp; V. Allen &amp; P. J. Makovicky" box="[1255,1267,779,803]" journalOrPublisher="PLOs ONE" pageId="5" pageNumber="6" pagination="e 26037" part="6" refId="ref7327" refString="6. J. R. Hutchinson, K. T. Bates, J. Molnar, V. Allen, P. J. Makovicky, A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth. PLOs ONE 6, e 26037 (2011)." title="A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth" type="journal article" year="2011">
<emphasis id="B9352568FFE60E51FB395468FB7BFCAA" box="[1255,1267,779,803]" italics="true" pageId="5" pageNumber="6">6</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE60E51FB215468FA83FCAB" author="P. J. Currie" box="[1279,1291,779,802]" journalOrPublisher="Can. J. Earth sci." pageId="5" pageNumber="6" pagination="651 - 665" part="40" refId="ref7386" refString="7. P. J. Currie, Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia. Can. J. Earth sci. 40, 651 - 665 (2003)." title="Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia" type="journal article" year="2003">
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). Hutchinson
<emphasis id="B9352568FFE60E51FA415468FA59FCAA" box="[1439,1489,779,803]" italics="true" pageId="5" pageNumber="6">et al.</emphasis>
(
<bibRefCitation id="EFD0848BFFE60E51FCEF544BFCB5FCC9" author="J. R. Hutchinson &amp; K. T. Bates &amp; J. Molnar &amp; V. Allen &amp; P. J. Makovicky" box="[817,829,808,832]" journalOrPublisher="PLOs ONE" pageId="5" pageNumber="6" pagination="e 26037" part="6" refId="ref7327" refString="6. J. R. Hutchinson, K. T. Bates, J. Molnar, V. Allen, P. J. Makovicky, A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth. PLOs ONE 6, e 26037 (2011)." title="A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth" type="journal article" year="2011">
<emphasis id="B9352568FFE60E51FCEF544BFCB5FCC9" box="[817,829,808,832]" italics="true" pageId="5" pageNumber="6">6</emphasis>
</bibRefCitation>
) obtained an averaged body mass estimate of 954 kg for
<materialsCitation id="3B29F327FFE60E51FA53544AFCF5FCD4" ID-GBIF-Occurrence="3396425400" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
, which falls within the mid-sized dinosaur body mass range defined by Holtz (
<bibRefCitation id="EFD0848BFFE60E51FC055400FC7BFCF2" author="T. R. Holtz Jr." box="[987,1011,867,891]" journalOrPublisher="J. Vertebr. Paleontol." pageId="5" pageNumber="6" pagination="72 A" part="24" refId="ref8716" refString="35. T. R. Holtz Jr., Taxonomic diversity, morphological disparity, and guild structure in theropod carnivore communities: implications for paleoecology and life history strategies in tyrant dinosaurs. J. Vertebr. Paleontol. 24, 72 A (2004)." title="Taxonomic diversity, morphological disparity, and guild structure in theropod carnivore communities: implications for paleoecology and life history strategies in tyrant dinosaurs" type="journal article" year="2004">
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) as 50 to 1000 kg. Our histological confirmation of
<materialsCitation id="3B29F327FFE60E51FC9F54E2FC50FC11" ID-GBIF-Occurrence="3396425316" box="[833,984,896,920]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
<materialsCitation id="3B29F327FFE60E51FBD754E2FB28FC11" ID-GBIF-Occurrence="3396425406" box="[1033,1184,896,920]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
as mid-sized juveniles is therefore congruent with a hypothesized delayed onset of exponential growth in
<taxonomicName id="4C4182F9FFE60E51FC9C54D8FCF4FC5B" authorityName="Osborn" authorityYear="1905" box="[834,892,955,978]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FC9C54D8FCF4FC5B" box="[834,892,955,978]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
relative to the ontogenetic timing of exponential growth in other tyrannosaurids (
<bibRefCitation id="EFD0848BFFE60E51FBD754BBFB9DFC79" author="G. M. Erickson &amp; P. J. Makovicky &amp; P. J. Currie &amp; M. A. Norell &amp; S. A. Yerby &amp; C. A. Brochu" box="[1033,1045,984,1008]" journalOrPublisher="Nature" pageId="5" pageNumber="6" pagination="772 - 775" part="430" refId="ref7228" refString="4. G. M. Erickson, P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, C. A. Brochu, Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature 430, 772 - 775 (2004)." title="Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs" type="journal article" year="2004">
<emphasis id="B9352568FFE60E51FBD754BBFB9DFC79" box="[1033,1045,984,1008]" italics="true" pageId="5" pageNumber="6">4</emphasis>
</bibRefCitation>
). Because
<taxonomicName id="4C4182F9FFE60E51FBA054BAFB3FFC79" authorityName="Osborn" authorityYear="1905" box="[1150,1207,985,1008]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FBA054BAFB3FFC79" box="[1150,1207,985,1008]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
attained its great size late in ontogeny (
<bibRefCitation id="EFD0848BFFE60E51FC515495FC12FB87" author="G. M. Erickson &amp; P. J. Makovicky &amp; P. J. Currie &amp; M. A. Norell &amp; S. A. Yerby &amp; C. A. Brochu" box="[911,922,1014,1038]" journalOrPublisher="Nature" pageId="5" pageNumber="6" pagination="772 - 775" part="430" refId="ref7228" refString="4. G. M. Erickson, P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, C. A. Brochu, Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature 430, 772 - 775 (2004)." title="Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs" type="journal article" year="2004">
<emphasis id="B9352568FFE60E51FC515495FC12FB87" box="[911,922,1014,1038]" italics="true" pageId="5" pageNumber="6">4</emphasis>
</bibRefCitation>
), many aspects of its biology likely differed between juvenile and adult individuals, leading to hypotheses that it used ontogenetic niche partitioning (
<bibRefCitation id="EFD0848BFFE60E51FC3A5353FC78FBC1" author="S. L. Brusatte &amp; M. A. Norell &amp; T. D. Carr &amp; G. M. Erickson &amp; J. R. Hutchinson &amp; A. M. Balanoff &amp; G. S. Bever &amp; J. N. Choiniere &amp; P. J. Makovicky &amp; X. Xu" box="[996,1008,1072,1096]" journalOrPublisher="science" pageId="5" pageNumber="6" pagination="1481 - 1485" part="329" refId="ref7118" refString="2. S. L. Brusatte, M. A. Norell, T. D. Carr, G. M. Erickson, J. R. Hutchinson, A. M. Balanoff, G. S. Bever, J. N. Choiniere, P. J. Makovicky, X. Xu, Tyrannosaur paleobiology: New research on ancient exemplar organisms. science 329, 1481 - 1485 (2010)." title="Tyrannosaur paleobiology: New research on ancient exemplar organisms" type="journal article" year="2010">
<emphasis id="B9352568FFE60E51FC3A5353FC78FBC1" box="[996,1008,1072,1096]" italics="true" pageId="5" pageNumber="6">2</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE60E51FC245353FB99FBC1" author="T. R. Holtz Jr." box="[1018,1041,1072,1096]" editor="P. Larson &amp; K. Carpenter" journalOrPublisher="Indiana Univ. Press, Bloomington" pageId="5" pageNumber="6" pagination="371 - 396" part="chap. 20" refId="ref8765" refString="36. T. R. Holtz Jr., Tyrannosaurus rex, the Tyrant King, P. Larson, K. Carpenter, Eds. (Indiana Univ. Press, Bloomington, 2008), chap. 20, pp. 371 - 396." title="Tyrannosaurus rex, the Tyrant King" type="journal article" year="2008">
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,
<bibRefCitation id="EFD0848BFFE60E51FBC25353FBBBFBC1" author="A. Kane &amp; K. Healy &amp; G. D. Ruxton &amp; A. L. Jackson" box="[1052,1075,1072,1096]" journalOrPublisher="Am. Nat." pageId="5" pageNumber="6" pagination="706 - 716" part="187" refId="ref8813" refString="37. A. Kane, K. Healy, G. D. Ruxton, A. L. Jackson, Body size as a driver of scavenging in theropod dinosaurs. Am. Nat. 187, 706 - 716 (2016)." title="Body size as a driver of scavenging in theropod dinosaurs" type="journal article" year="2016">
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), where prey size is a function of body size (
<bibRefCitation id="EFD0848BFFE60E51FCEE532DFCB4FBEF" author="S. L. Brusatte &amp; M. A. Norell &amp; T. D. Carr &amp; G. M. Erickson &amp; J. R. Hutchinson &amp; A. M. Balanoff &amp; G. S. Bever &amp; J. N. Choiniere &amp; P. J. Makovicky &amp; X. Xu" box="[816,828,1102,1126]" journalOrPublisher="science" pageId="5" pageNumber="6" pagination="1481 - 1485" part="329" refId="ref7118" refString="2. S. L. Brusatte, M. A. Norell, T. D. Carr, G. M. Erickson, J. R. Hutchinson, A. M. Balanoff, G. S. Bever, J. N. Choiniere, P. J. Makovicky, X. Xu, Tyrannosaur paleobiology: New research on ancient exemplar organisms. science 329, 1481 - 1485 (2010)." title="Tyrannosaur paleobiology: New research on ancient exemplar organisms" type="journal article" year="2010">
<emphasis id="B9352568FFE60E51FCEE532DFCB4FBEF" box="[816,828,1102,1126]" italics="true" pageId="5" pageNumber="6">2</emphasis>
</bibRefCitation>
,
<bibRefCitation id="EFD0848BFFE60E51FC99532EFCD6FBEC" author="T. R. Holtz Jr." box="[839,862,1101,1125]" editor="P. Larson &amp; K. Carpenter" journalOrPublisher="Indiana Univ. Press, Bloomington" pageId="5" pageNumber="6" pagination="371 - 396" part="chap. 20" refId="ref8765" refString="36. T. R. Holtz Jr., Tyrannosaurus rex, the Tyrant King, P. Larson, K. Carpenter, Eds. (Indiana Univ. Press, Bloomington, 2008), chap. 20, pp. 371 - 396." title="Tyrannosaurus rex, the Tyrant King" type="journal article" year="2008">
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,
<bibRefCitation id="EFD0848BFFE60E51FCB7532DFC08FBEF" author="D. A. Russell" box="[873,896,1102,1126]" journalOrPublisher="National Museum of Natural sciences, Publications, in Paleontology" pageId="5" pageNumber="6" pagination="1 - 34" part="1" refId="ref8859" refString="38. D. A. Russell, Tyrannosaurs from the Late Cretaceous of western Canada. National Museum of Natural sciences, Publications, in Paleontology 1, 1 - 34 (1970)." title="Tyrannosaurs from the Late Cretaceous of western Canada" type="journal article" year="1970">
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). This feeding strategy is observed today in the extant archosaur
<taxonomicName id="4C4182F9FFE60E51FC875308FC38FB0A" box="[857,944,1131,1155]" class="Reptilia" family="Alligatoridae" genus="Alligator" kingdom="Animalia" order="Crocodylia" pageId="5" pageNumber="6" phylum="Chordata" rank="genus">
<emphasis id="B9352568FFE60E51FC875308FC38FB0A" box="[857,944,1131,1155]" italics="true" pageId="5" pageNumber="6">Alligator</emphasis>
</taxonomicName>
, because it occupies different carnivore niches before and after achieving skeletal maturity (
<bibRefCitation id="EFD0848BFFE60E51FB4B53EBFB24FB29" author="P. Dodson" box="[1173,1196,1160,1184]" journalOrPublisher="J. Zool." pageId="5" pageNumber="6" pagination="315 - 355" part="175" refId="ref8895" refString="39. P. Dodson, Functional and ecological significance of relative growth in Alligator. J. Zool. 175, 315 - 355 (1975)." title="Functional and ecological significance of relative growth in Alligator" type="journal article" year="1975">
<emphasis id="B9352568FFE60E51FB4B53EBFB24FB29" box="[1173,1196,1160,1184]" italics="true" pageId="5" pageNumber="6">39</emphasis>
</bibRefCitation>
). Most recently, Peterson and Daus (
<bibRefCitation id="EFD0848BFFE60E51FCB253C5FC0CFB37" author="J. E. Peterson &amp; K. N. Daus" box="[876,900,1190,1214]" journalOrPublisher="PeerJ" pageId="5" pageNumber="6" pagination="e 6573" part="7" refId="ref8924" refString="40. J. E. Peterson, K. N. Daus, Feeding traces attributable to juvenile Tyrannosaurus rex offer insight into ontogenetic dietary trends. PeerJ 7, e 6573 (2019)." title="Feeding traces attributable to juvenile Tyrannosaurus rex offer insight into ontogenetic dietary trends" type="journal article" year="2019">
<emphasis id="B9352568FFE60E51FCB253C5FC0CFB37" box="[876,900,1190,1214]" italics="true" pageId="5" pageNumber="6">40</emphasis>
</bibRefCitation>
) demonstrated that although able to puncture bone, latestage juvenile
<taxonomicName id="4C4182F9FFE60E51FC7153A0FC6FFB53" authorityName="Osborn" authorityYear="1905" box="[943,999,1219,1242]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FC7153A0FC6FFB53" box="[943,999,1219,1242]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
could not yet crush bone or engage in osteophagy, and therefore engaged in a feeding strategy distinct from adults.
</paragraph>
<paragraph id="8BFEF97AFFE60E51FC96539DFA81FA4C" blockId="5.[808,1489,542,1477]" pageId="5" pageNumber="6">
Our histological assessment of
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and
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provides data critical to understanding juvenile
<taxonomicName id="4C4182F9FFE60E51FABF527FFA13FABA" authorityName="Osborn" authorityYear="1905" box="[1377,1435,1308,1331]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FABF527FFA13FABA" box="[1377,1435,1308,1331]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
biology and ecology, and additional evidence that there were no sympatric tyrannosaurids in the HCF. Furthermore, we hypothesize that ontogenetic niche partitioning, coupled with an ability to adjust annual growth hiatus duration to track resource abundance, made
<taxonomicName id="4C4182F9FFE60E51FA4652F2FA47FA21" authorityName="Osborn" authorityYear="1905" box="[1432,1487,1425,1448]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="5" pageNumber="6" phylum="Chordata" rank="species" species="rex">
<emphasis id="B9352568FFE60E51FA4652F2FA47FA21" box="[1432,1487,1425,1448]" italics="true" pageId="5" pageNumber="6">T. rex</emphasis>
</taxonomicName>
one of the most successful nonavian theropods.
</paragraph>
</subSubSection>
<subSubSection id="C35BAAF1FFE60E52FCF65166FBC3FE74" lastPageId="6" lastPageNumber="7" pageId="5" pageNumber="6" type="description">
<paragraph id="8BFEF97AFFE60E51FCF65166FBC4F995" blockId="5.[808,1488,1541,1771]" box="[808,1100,1541,1565]" pageId="5" pageNumber="6">
<heading id="D0B64E16FFE60E51FCF65166FBC4F995" allCaps="true" bold="true" box="[808,1100,1541,1565]" fontSize="9" level="2" pageId="5" pageNumber="6" reason="6">
<emphasis id="B9352568FFE60E51FCF65166FBC4F995" bold="true" box="[808,1100,1541,1565]" pageId="5" pageNumber="6">MATERIALS AND METHODS</emphasis>
</heading>
</paragraph>
<paragraph id="8BFEF97AFFE60E51FCF65140FB3EF962" blockId="5.[808,1488,1541,1771]" pageId="5" pageNumber="6">
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and
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were collected from the HCF of Carter County, Montana. The specimen
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consists of a nearly complete skull with associated postcrania, including a partial femur [estimated length, 68.8 cm; (
<bibRefCitation id="EFD0848BFFE60E51FB7C5118FB26F91B" author="P. J. Currie" box="[1186,1198,1659,1682]" journalOrPublisher="Can. J. Earth sci." pageId="5" pageNumber="6" pagination="651 - 665" part="40" refId="ref7386" refString="7. P. J. Currie, Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia. Can. J. Earth sci. 40, 651 - 665 (2003)." title="Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia" type="journal article" year="2003">
<emphasis id="B9352568FFE60E51FB7C5118FB26F91B" box="[1186,1198,1659,1682]" italics="true" pageId="5" pageNumber="6">7</emphasis>
</bibRefCitation>
)] and complete tibiae.
<materialsCitation id="3B29F327FFE60E51FA535118FCF5F939" ID-GBIF-Occurrence="3396425407" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
is far less complete and lacks cranial material, but with a femur length of 77.4 cm, it is slightly larger (and presumably ontogenetically older) than
<materialsCitation id="3B29F327FFE60E51FBCF51B0FB3AF962" ID-GBIF-Occurrence="3396425303" box="[1041,1202,1747,1771]" collectionCode="BMRP" pageId="5" pageNumber="6" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
.
</paragraph>
<paragraph id="8BFEF97AFFE60E51FCF6506FFB87F8AC" blockId="5.[808,1488,1804,1888]" box="[808,1039,1804,1829]" pageId="5" pageNumber="6">
<heading id="D0B64E16FFE60E51FCF6506FFB87F8AC" bold="true" box="[808,1039,1804,1829]" fontSize="10" level="3" pageId="5" pageNumber="6" reason="0">
<emphasis id="B9352568FFE60E51FCF6506FFB87F8AC" bold="true" box="[808,1039,1804,1829]" pageId="5" pageNumber="6">Histological analysis</emphasis>
</heading>
</paragraph>
<paragraph id="8BFEF97AFFE60E52FCF65049FF65FE01" blockId="5.[808,1488,1804,1888]" lastBlockId="6.[96,777,162,1888]" lastPageId="6" lastPageNumber="7" pageId="5" pageNumber="6">
The partial femur of
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and the partial tibia of
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were histologically processed by the MOR for an earlier project, and the resulting thin section slides were made available on loan to the senior author. Additional thin sections were produced for the current study to directly compare histological features across bones of
<materialsCitation id="3B29F327FFE50E52FF615798FED7FE9A" ID-GBIF-Occurrence="3396425359" box="[191,351,251,275]" collectionCode="BMRP" pageId="6" pageNumber="7" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
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: Full transverse thin sections from the femur of
<materialsCitation id="3B29F327FFE50E52FEA4567BFD91FEB9" ID-GBIF-Occurrence="3396425321" box="[378,537,280,304]" collectionCode="BMRP" pageId="6" pageNumber="7" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
and the tibia of
<materialsCitation id="3B29F327FFE50E52FD1B567BFF3DFEC4" ID-GBIF-Occurrence="3396425370" collectionCode="BMRP" pageId="6" pageNumber="7" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
were produced following the methodology of Padian and Lamm (
<bibRefCitation id="EFD0848BFFE50E52FF6C5630FF42FEE2" author="K. Padian &amp; E. - T. Lamm" box="[178,202,339,363]" journalOrPublisher="University of California Press, Berkeley" pageId="6" pageNumber="7" pagination="285" refId="ref7502" refString="10. K. Padian, E. - T. Lamm, Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation (University of California Press, Berkeley, 2013), p. 285." title="Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation" type="book chapter" year="2013">
<emphasis id="B9352568FFE50E52FF6C5630FF42FEE2" box="[178,202,339,363]" italics="true" pageId="6" pageNumber="7">10</emphasis>
</bibRefCitation>
) with the permission of BMRP and the Bureau of Land Management.
</paragraph>
<paragraph id="8BFEF97AFFE50E52FF5E56EEFD21FDB1" blockId="6.[96,777,162,1888]" pageId="6" pageNumber="7">
Fibula thin section slides of
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and
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were earlier produced for separate projects. An ontogenetic age of 11 for
<materialsCitation id="3B29F327FFE50E52FF7E56ABFEB4FE69" ID-GBIF-Occurrence="3396425350" box="[160,316,456,480]" collectionCode="BMRP" pageId="6" pageNumber="7" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
was published by Erickson (
<bibRefCitation id="EFD0848BFFE50E52FD8956ABFDEBFE69" author="G. M. Erickson" box="[599,611,456,480]" journalOrPublisher="Trends Ecol. Evol." pageId="6" pageNumber="7" pagination="677 - 684" part="20" refId="ref7429" refString="8. G. M. Erickson, Assessing dinosaur growth patterns: A microscopic revolution. Trends Ecol. Evol. 20, 677 - 684 (2005)." title="Assessing dinosaur growth patterns: A microscopic revolution" type="journal article" year="2005">
<emphasis id="B9352568FFE50E52FD8956ABFDEBFE69" box="[599,611,456,480]" italics="true" pageId="6" pageNumber="7">8</emphasis>
</bibRefCitation>
) based on fibula histology, and an ontogenetic age of
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was not published. Access to the aforementioned fibula thin sections for comparative histology and skeletochronology in this study was denied.
</paragraph>
<paragraph id="8BFEF97AFFE50E52FF5E555EFD1DFB52" blockId="6.[96,777,162,1888]" pageId="6" pageNumber="7">
As summarized by Prondvai
<emphasis id="B9352568FFE50E52FE43555DFE44FDDC" box="[413,460,573,597]" italics="true" pageId="6" pageNumber="7">et al.</emphasis>
(
<bibRefCitation id="EFD0848BFFE50E52FE07555EFE78FDDC" author="E. Prondvai &amp; K. H. W. Stein &amp; A. de Ricqles &amp; J. Cubo" box="[473,496,573,597]" journalOrPublisher="Biol. J. Linn. soc." pageId="6" pageNumber="7" pagination="799 - 816" part="112" refId="ref7631" refString="13. E. Prondvai, K. H. W. Stein, A. de Ricqles, J. Cubo, Development-based revision of bone tissue classification: the importance of semantics for science. Biol. J. Linn. soc. 112, 799 - 816 (2014)." title="Development-based revision of bone tissue classification: the importance of semantics for science" type="journal article" year="2014">
<emphasis id="B9352568FFE50E52FE07555EFE78FDDC" box="[473,496,573,597]" italics="true" pageId="6" pageNumber="7">13</emphasis>
</bibRefCitation>
), modern bone is composed of integrated hydroxyapatite crystals and collagen fibrils, with long axes arranged in parallel. Thus, the orientation of inorganic hydroxyapatite minerals implies collagen fiber arrangement in fossil bone, and this orientation can be inferred visually by the intensity of birefringence associated with anisotropy in polarized light: If the fiber bundles are cut across their longitudinal axis, they will appear bright (anisotropic), whereas if cut transversely, they will remain dark (isotropic). Bone fiber orientation is typically diagnosed from a thin section of bone cut transverse to the long axis of a diaphysis. Bone tissue was classified as parallel fibered or lamellar if uniformly anisotropic with flattened osteocyte lacunae (i.e., lacuna long axis parallel to fiber orientation) and woven if uniformly isotropic with rounded lacunae. Without examining bone tissue in the longitudinal as well as transverse planes, it is impossible to distinguish woven tissue, which should remain isotropic in both orientations, from longitudinally oriented parallel-fibered or lamellar tissue, which is isotropic in the transverse section and can therefore be mistaken for woven tissue. This distinction is critical, because ranges of daily apposition rates are frequently assigned on the basis of fiber orientation [see (
<bibRefCitation id="EFD0848BFFE50E52FD4A5308FD24FB0A" author="E. Prondvai &amp; K. H. W. Stein &amp; A. de Ricqles &amp; J. Cubo" box="[660,684,1131,1155]" journalOrPublisher="Biol. J. Linn. soc." pageId="6" pageNumber="7" pagination="799 - 816" part="112" refId="ref7631" refString="13. E. Prondvai, K. H. W. Stein, A. de Ricqles, J. Cubo, Development-based revision of bone tissue classification: the importance of semantics for science. Biol. J. Linn. soc. 112, 799 - 816 (2014)." title="Development-based revision of bone tissue classification: the importance of semantics for science" type="journal article" year="2014">
<emphasis id="B9352568FFE50E52FD4A5308FD24FB0A" box="[660,684,1131,1155]" italics="true" pageId="6" pageNumber="7">13</emphasis>
</bibRefCitation>
) for discussion]. For this reason, when thin sections were produced for this study, each specimen was sectioned both longitudinally and transversely to more accurately assess bone fiber orientation.
</paragraph>
<paragraph id="8BFEF97AFFE50E52FF5E5383FEEEF926" blockId="6.[96,777,162,1888]" pageId="6" pageNumber="7">
Full transverse sections from the femoral and tibial diaphyses of
<materialsCitation id="3B29F327FFE50E52FFBE539DFF77FA9C" ID-GBIF-Occurrence="3396425386" box="[96,255,1277,1301]" collectionCode="BMRP" pageId="6" pageNumber="7" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and
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were removed from the bones using a circular saw with a continuous rim diamond blade. The samples removed were molded and cast, and the cast replicas were restored to the fossil bones. The samples removed were then embedded in Silmar polyester resin, and transverse wafers were cut (~3 to 4 mm thick) to either side of the line of minimum circumference with a circular saw and continuous rim diamond blade. These wafers were glued to frosted glass slides and polished on a variable speed grinder to mirror finish using a series of 60, 120, 180, 320, 600, 800, and 1200 silicon carbide grit papers and 5- and 1-μ m hand-polish slurries. Final slide thicknesses were between 97 and 177 μ m. Longitudinal sections were made from the embedded diaphysis samples, along a lateral-medial plane in the tibia of
<materialsCitation id="3B29F327FFE50E52FE7B513DFDB3F9FC" ID-GBIF-Occurrence="3396425327" box="[421,571,1629,1653]" collectionCode="BMRP" pageId="6" pageNumber="7" specimenCode="BMRP 2002.4.1">BMRP 2002.4.1</materialsCitation>
and an anterolateralposteromedial plane in the femur of
<materialsCitation id="3B29F327FFE50E52FE0B5118FDFDF91A" ID-GBIF-Occurrence="3396425410" box="[469,629,1659,1683]" collectionCode="BMRP" pageId="6" pageNumber="7" specimenCode="BMRP 2006.4.4">BMRP 2006.4.4</materialsCitation>
, capturing the thickest regions of cortex.
</paragraph>
<paragraph id="8BFEF97AFFE50E52FF5E51D6FBC3FE74" blockId="6.[96,777,162,1888]" lastBlockId="6.[808,1488,163,509]" pageId="6" pageNumber="7">
Thin sections were analyzed using a Nikon Eclipse Ni-U polarizing microscope and plane-polarized light (i.e., only the polarizer in position), CPL, and cross-polarized light with 540-nm lambda filter. Photomicrographs were taken using a Nikon Fi2 microscope camera. Composite images of each full thin section at ×20 total magnification were obtained through the use of an automated Applied Scientific Instrumentation microscope stage and Nikon Elements: Documentation software. Annually formed CGMs, including LAGs and annuli, were identified and digitally traced using Adobe Photoshop CC. Comparisons of annual zonal thicknesses between CGMs were made along a transect, and measurements were taken in Adobe Photoshop CC. Histological descriptions were made from observations using CPL and follow the terminology of Padian and Lamm (
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<emphasis id="B9352568FFE50E52FA5B5630FA14FEE2" box="[1413,1436,339,363]" italics="true" pageId="6" pageNumber="7">10</emphasis>
</bibRefCitation>
) and Prondvai
<emphasis id="B9352568FFE50E52FC525612FC36FE01" box="[908,958,368,392]" italics="true" pageId="6" pageNumber="7">et al.</emphasis>
(
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<emphasis id="B9352568FFE50E52FC125613FC6CFE01" box="[972,996,368,392]" italics="true" pageId="6" pageNumber="7">13</emphasis>
</bibRefCitation>
). A CGM was identified as an annulus if it consisted of a diffuse band of parallel-fibered bone and interpreted as a period of considerably decreased osteogenesis. A LAG was identified as a thin hypermineralized ring, indicating a period when osteogenesis ceased altogether.
</paragraph>
</subSubSection>
</treatment>
</document>
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