301 lines
42 KiB
XML
301 lines
42 KiB
XML
<document id="0EDD3D5D4A082862267F5004C078E4FC" ID-DOI="10.1206/0003-0082(2006)500[0001:JOLCPA]2.0.CO;2" ID-ISSN="0003-0082" ID-Zenodo-Dep="5383501" IM.metadata_approvedBy="felipe" IM.taxonomicNames_approvedBy="felipe" checkinTime="1630296709165" checkinUser="carolina" docAuthor="LANDMAN, NEIL H., TSUJITA, CAMERON J., COBBAN, WILLIAM A., LARSON, NEAL L., TANABE, KAZUSHIGE & FLEMMING, ROBERTA L." docDate="2006" docId="03BB87A41511FFA1FD62FC9BFEAA8AC0" docLanguage="en" docName="N3500.pdf" docOrigin="American Museum Novitates 3500" docSource="http://www.bioone.org/doi/abs/10.1206/0003-0082%282006%29500%5B0001%3AJOLCPA%5D2.0.CO%3B2" docStyle="DocumentStyle:70DDF1BDF6846024993F05262BAE3001.3:AmMusNovit.2000-2010.journal_article.type1" docStyleId="70DDF1BDF6846024993F05262BAE3001" docStyleName="AmMusNovit.2000-2010.journal_article.type1" docStyleVersion="3" docTitle="Metaplacenticeras subtilistriatum" docType="treatment" docVersion="3" lastPageNumber="33" masterDocId="FF82FFDC150DFF83FF9DFFFFFFBA8E27" masterDocTitle="Jaws of Late Cretaceous Placenticeratid Ammonites: How Preservation Affects the Interpretation of Morphology" masterLastPageNumber="48" masterPageNumber="1" pageNumber="29" updateTime="1699219141465" updateUser="plazi" zenodo-license-document="CC-BY-4.0">
|
||
<mods:mods id="35775E658181D749375A76B7D38B8EE8" xmlns:mods="http://www.loc.gov/mods/v3">
|
||
<mods:titleInfo id="08B39749D0C12385357337A9EDAAC056">
|
||
<mods:title id="85C595CEEE57C6278D7DB473B5C945F4">Jaws of Late Cretaceous Placenticeratid Ammonites: How Preservation Affects the Interpretation of Morphology</mods:title>
|
||
</mods:titleInfo>
|
||
<mods:name id="361115C89BCF922B057A6E80B657CD29" type="personal">
|
||
<mods:role id="6E75D2253E31EC26DB9487D0533AC0C5">
|
||
<mods:roleTerm id="D6FA95965E8A3254019F470EF0C43F6E">Author</mods:roleTerm>
|
||
</mods:role>
|
||
<mods:namePart id="73996D1056080F1AA4ED418B7BA2D024">LANDMAN, NEIL H.</mods:namePart>
|
||
</mods:name>
|
||
<mods:name id="806BEF46ECA45463B204F20A0D54CE51" type="personal">
|
||
<mods:role id="647C54D5C11C4FC85114412AE68B3B83">
|
||
<mods:roleTerm id="6BC72112A051C5DD593E8C82FC3D8742">Author</mods:roleTerm>
|
||
</mods:role>
|
||
<mods:namePart id="C54A4F9FBA95EEE0EBAFFB871910CF03">TSUJITA, CAMERON J.</mods:namePart>
|
||
</mods:name>
|
||
<mods:name id="1CCA4FFCEC3D3C8DCFEC8D47162F8797" type="personal">
|
||
<mods:role id="AD03C7CDCA578242CEB55527543DFB96">
|
||
<mods:roleTerm id="B046FDED1974427D12E469499C518040">Author</mods:roleTerm>
|
||
</mods:role>
|
||
<mods:namePart id="4C0727AECEFB4D9FD8788EE4E9F0BCB3">COBBAN, WILLIAM A.</mods:namePart>
|
||
</mods:name>
|
||
<mods:name id="FA8B2B7E0C8A14486AAF6FDDE26E2347" type="personal">
|
||
<mods:role id="940C7928A8FB945221280E28596A3725">
|
||
<mods:roleTerm id="F4B80C374372B83ACD6C703E7B8A1A83">Author</mods:roleTerm>
|
||
</mods:role>
|
||
<mods:namePart id="81225C3039A42FD7C360FE5EB8D335C1">LARSON, NEAL L.</mods:namePart>
|
||
</mods:name>
|
||
<mods:name id="D9E53BB245CC03DE1974989393E1E0E9" type="personal">
|
||
<mods:role id="FA64824ABE4002A790C1BC0D581FFCFB">
|
||
<mods:roleTerm id="00C698EB868137009AB8F5CA38BEF845">Author</mods:roleTerm>
|
||
</mods:role>
|
||
<mods:namePart id="070271012441EF9BCD43F49EF3FDA46E">TANABE, KAZUSHIGE</mods:namePart>
|
||
</mods:name>
|
||
<mods:name id="19B9D13B02FAA6871371C0BEA3B4BA28" type="personal">
|
||
<mods:role id="5ACB5196865F782E2BFD791A8F17713A">
|
||
<mods:roleTerm id="69F1893F3299B140D5AD2002846415C4">Author</mods:roleTerm>
|
||
</mods:role>
|
||
<mods:namePart id="10CF7D5350C2A0B2716919B05C31CBA3">FLEMMING, ROBERTA L.</mods:namePart>
|
||
</mods:name>
|
||
<mods:typeOfResource id="905DEE317EE966212201CEF98521EC42">text</mods:typeOfResource>
|
||
<mods:relatedItem id="0702312032F9C49057AD2CBDA69D2018" type="host">
|
||
<mods:titleInfo id="719944AC5254EB3EEBED4BCB51E2B87B">
|
||
<mods:title id="80281DED3FAE3D5460F5A946978F1584">American Museum Novitates</mods:title>
|
||
</mods:titleInfo>
|
||
<mods:part id="20FD8FAB404972929067E39AFDBD65EA">
|
||
<mods:date id="537AA42B23167F347447ED5F46540861">2006</mods:date>
|
||
<mods:detail id="5FCE7137439B30F616C4E50E89B08268" type="pubDate">
|
||
<mods:number id="996A9C9B5729C73F92AFC99FC78CB880">2006-01-12</mods:number>
|
||
</mods:detail>
|
||
<mods:detail id="4039428B73FFB05E745C7ECBB7938F2A" type="volume">
|
||
<mods:number id="8FB966E65235B5E4722340FBC0F90A56">3500</mods:number>
|
||
</mods:detail>
|
||
<mods:extent id="36EC0DDAE1454B2C297344D808983EC8" unit="page">
|
||
<mods:start id="935B6CD775ABF7F8A21C2D4567495EA0">1</mods:start>
|
||
<mods:end id="1E1B922AF3829D7EBE86D01AB35D7311">48</mods:end>
|
||
</mods:extent>
|
||
</mods:part>
|
||
</mods:relatedItem>
|
||
<mods:location id="50581D687101934AF4F7E64FCB09149C">
|
||
<mods:url id="0B3B2DC72F227B3915CACCC65AEC2B23">http://www.bioone.org/doi/abs/10.1206/0003-0082%282006%29500%5B0001%3AJOLCPA%5D2.0.CO%3B2</mods:url>
|
||
</mods:location>
|
||
<mods:classification id="288031F0644393922D69848FFC161DFF">journal article</mods:classification>
|
||
<mods:identifier id="1647A34E80A30F8FD23469A58841FE75" type="DOI">10.1206/0003-0082(2006)500[0001:JOLCPA]2.0.CO;2</mods:identifier>
|
||
<mods:identifier id="75C642F5CC2704C957AA2780EE1D6135" type="ISSN">0003-0082</mods:identifier>
|
||
<mods:identifier id="67F1E0A8E52DBCA8C9B0721A8996E497" type="Zenodo-Dep">5383501</mods:identifier>
|
||
</mods:mods>
|
||
<treatment id="03BB87A41511FFA1FD62FC9BFEAA8AC0" LSID="urn:lsid:plazi:treatment:03BB87A41511FFA1FD62FC9BFEAA8AC0" httpUri="http://treatment.plazi.org/id/03BB87A41511FFA1FD62FC9BFEAA8AC0" lastPageId="34" lastPageNumber="33" pageId="28" pageNumber="29">
|
||
<subSubSection id="C30865391511FF9FFD62FC9BFB808D80" pageId="28" pageNumber="29" type="nomenclature">
|
||
<paragraph id="8BAD36B21511FF9FFD62FC9BFB318D5C" blockId="28.[767,1163,868,891]" box="[767,1163,868,891]" pageId="28" pageNumber="29">
|
||
<heading id="D0E581DE1511FF9FFD62FC9BFB318D5C" box="[767,1163,868,891]" centered="true" fontSize="36" level="2" pageId="28" pageNumber="29" reason="8">
|
||
<taxonomicName id="4C124D311511FF9FFD62FC9BFB318D5C" ID-CoL="42CBR" baseAuthorityName="Jimbo" baseAuthorityYear="1894" box="[767,1163,868,891]" class="Cephalopoda" family="Placenticeratidae" genus="Metaplacenticeras" kingdom="Animalia" order="Ammonoidea" pageId="28" pageNumber="29" phylum="Mollusca" rank="species" species="subtilistriatum">
|
||
<emphasis id="B966EAA01511FF9FFD62FC9BFB318D5C" box="[767,1163,868,891]" italics="true" pageId="28" pageNumber="29">Metaplacenticeras subtilistriatum</emphasis>
|
||
</taxonomicName>
|
||
</heading>
|
||
</paragraph>
|
||
<paragraph id="8BAD36B21511FF9FFD21FC6FFB808D80" blockId="28.[700,1082,912,935]" box="[700,1082,912,935]" pageId="28" pageNumber="29">
|
||
Yasukawa Formation,
|
||
<collectingRegion id="49D6F8501511FF9FFC5AFC6FFB808D80" box="[967,1082,912,935]" country="Japan" name="Hokkaido" pageId="28" pageNumber="29">Hokkaido</collectingRegion>
|
||
</paragraph>
|
||
</subSubSection>
|
||
<subSubSection id="C30865391511FFA1FD44FC43FEAA8AC0" lastPageId="34" lastPageNumber="35" pageId="28" pageNumber="29" type="description">
|
||
<paragraph id="8BAD36B21511FF9FFD44FC43FBE58AA4" blockId="28.[700,1229,956,1741]" pageId="28" pageNumber="29">
|
||
UMUT MM28896 is a lower jaw that occurs in a calcareous concretion with numerous plant fragments and shells (
|
||
<figureCitation id="13292A371511FF9FFBAAFC09FB738A2A" box="[1079,1225,1014,1037]" captionStart="Fig" captionStartId="34.[150,188,1587,1608]" captionText="Fig. 26. Lower jaws attributed to Metaplacenticeras subtilistriatum (Jimbo, 1894), Hokkaido, Japan. A–D. UMUT MM28897. A. Ventral view, anterior end on left, showing undulations paralleling the posterior margin. B. Closeup of the anterior end. C. Right lateral view. D. Left lateral view. E–H. UMUT MM28896. E. Ventral view, anterior end on left. The right wing is crumpled. F. Closeup of the anterior area showing fragments of the calcitic plate (arrow). G. Right lateral view. H. Left lateral view. Scale bar 5 5 mm." pageId="28" pageNumber="29">figs. 26E–H</figureCitation>
|
||
,
|
||
<figureCitation id="13292A371511FF9FFD21FBEBFD678A0C" box="[700,733,1044,1067]" captionStart="Fig" captionStartId="34.[150,188,892,913]" captionTargetBox="[130,649,186,872]" captionTargetId="figure-19@34.[130,649,186,872]" captionTargetPageId="34" captionText="Fig. 27. Drawing of the left wing of the lower jaw of UMUT MM28896 (see fig. 26E–H), showing pieces of the outer calcitic layer (dotted area). Texture as defined in figure 4." figureDoi="http://doi.org/10.5281/zenodo.5383558" httpUri="https://zenodo.org/record/5383558/files/figure.png" pageId="28" pageNumber="29">27</figureCitation>
|
||
). It is
|
||
<quantity id="4CEA9B571511FF9FFCB3FBEBFC238A0C" box="[814,921,1044,1067]" metricMagnitude="-2" metricUnit="m" metricValue="2.54" pageId="28" pageNumber="29" unit="mm" value="25.4">25.4 mm</quantity>
|
||
long and the left wing is
|
||
<quantity id="4CEA9B571511FF9FFD21FBCEFC9E8A6F" box="[700,804,1073,1096]" metricMagnitude="-2" metricUnit="m" metricValue="1.34" pageId="28" pageNumber="29" unit="mm" value="13.4">13.4 mm</quantity>
|
||
wide (W/L of the left wing 5 0.53). The jaw is folded along the midline with most of the right wing smashed in.
|
||
</paragraph>
|
||
<paragraph id="8BAD36B21511FF9FFD44FB76FBCF8B77" blockId="28.[700,1229,956,1741]" pageId="28" pageNumber="29">The anterior margin is slightly indented on each side of the apex. The apical angle is approximately 1308. There is a steplike feature near the anterior margin but most of the space between this feature and the anterior margin is filled in with coarsely crystalline black material eliminating any relief.</paragraph>
|
||
<paragraph id="8BAD36B21511FF9FFD44FAA9FB1B883A" blockId="28.[700,1229,956,1741]" pageId="28" pageNumber="29">
|
||
A narrow slit
|
||
<quantity id="4CEA9B571511FF9FFC19FAA9FC548B4A" box="[900,1006,1366,1389]" metricMagnitude="-4" metricUnit="m" metricValue="1.5" pageId="28" pageNumber="29" unit="mm" value="0.15">0.15 mm</quantity>
|
||
wide is present at the apex and extends approximately
|
||
<quantity id="4CEA9B571511FF9FFBF1FA8BFB728BAC" box="[1132,1224,1396,1419]" metricMagnitude="-3" metricUnit="m" metricValue="1.5" pageId="28" pageNumber="29" unit="mm" value="1.5">1.5 mm</quantity>
|
||
, after which it is covered in black material for a distance of
|
||
<quantity id="4CEA9B571511FF9FFCF4FA51FC0C8BE2" box="[873,950,1454,1477]" metricMagnitude="-3" metricUnit="m" metricValue="1.0" pageId="28" pageNumber="29" unit="mm" value="1.0">1 mm</quantity>
|
||
. It is subsequently replaced by a narrow groove
|
||
<quantity id="4CEA9B571511FF9FFC64FA33FB868BC4" box="[1017,1084,1484,1507]" metricMagnitude="-3" metricUnit="m" metricValue="3.0" pageId="28" pageNumber="29" unit="mm" value="3.0">3 mm</quantity>
|
||
long, which is bordered by narrow ridges on each side, posterior of which, the jaw is torn apart.
|
||
</paragraph>
|
||
<paragraph id="8BAD36B21511FF9EFD44F9DBFEC38AFC" blockId="28.[700,1229,956,1741]" lastBlockId="29.[123,652,1044,1741]" lastPageId="29" lastPageNumber="30" pageId="28" pageNumber="29">
|
||
The left wing consists of multiple layers. The basal layer is the steinkern, which is covered with coarsely crystalline black material. This layer is very thick in the median region and shows a honeycomblike texture. It is overlain by a very thin sheath of brown ish, finely crystalline material. This is overlain, in turn, by patches of a white crystalline layer approximately
|
||
<quantity id="4CEA9B571510FF9EFE12FBB1FE628A42" box="[399,472,1102,1125]" metricMagnitude="-3" metricUnit="m" metricValue="8.0" pageId="29" pageNumber="30" unit="mm" value="8.0">8 mm</quantity>
|
||
thick, which seems to be composed of elongate sections forming an angle of 458 with the midline (
|
||
<figureCitation id="13292A371510FF9EFF1EFB59FF568A9A" box="[131,236,1190,1213]" captionStart="Fig" captionStartId="34.[150,188,1587,1608]" captionText="Fig. 26. Lower jaws attributed to Metaplacenticeras subtilistriatum (Jimbo, 1894), Hokkaido, Japan. A–D. UMUT MM28897. A. Ventral view, anterior end on left, showing undulations paralleling the posterior margin. B. Closeup of the anterior end. C. Right lateral view. D. Left lateral view. E–H. UMUT MM28896. E. Ventral view, anterior end on left. The right wing is crumpled. F. Closeup of the anterior area showing fragments of the calcitic plate (arrow). G. Right lateral view. H. Left lateral view. Scale bar 5 5 mm." pageId="29" pageNumber="30">figs. 26F</figureCitation>
|
||
,
|
||
<figureCitation id="13292A371510FF9EFF67FB59FEA18A9A" box="[250,283,1190,1213]" captionStart="Fig" captionStartId="34.[150,188,892,913]" captionTargetBox="[130,649,186,872]" captionTargetId="figure-19@34.[130,649,186,872]" captionTargetPageId="34" captionText="Fig. 27. Drawing of the left wing of the lower jaw of UMUT MM28896 (see fig. 26E–H), showing pieces of the outer calcitic layer (dotted area). Texture as defined in figure 4." figureDoi="http://doi.org/10.5281/zenodo.5383558" httpUri="https://zenodo.org/record/5383558/files/figure.png" pageId="29" pageNumber="30">27</figureCitation>
|
||
). This layer may actually consist of two sublayers.
|
||
</paragraph>
|
||
<caption id="DF6D663A1510FF9EFF08FC6AFBC68DF8" ID-DOI="http://doi.org/10.5281/zenodo.5383550" ID-Zenodo-Dep="5383550" httpUri="https://zenodo.org/record/5383550/files/figure.png" pageId="29" pageNumber="30" startId="29.[149,187,917,938]" targetBox="[247,1102,186,896]" targetPageId="29">
|
||
<paragraph id="8BAD36B21510FF9EFF08FC6AFBC68DF8" blockId="29.[123,1227,917,991]" pageId="29" pageNumber="30">
|
||
Fig. 23. Parts of upper jaws (?) of
|
||
<taxonomicName id="4C124D311510FF9EFDAEFC6AFC1A8D8D" authority="Bohm, 1898" authorityName="Bohm" authorityYear="1898" box="[563,928,917,938]" class="Cephalopoda" family="Placenticeratidae" genus="Placenticeras" kingdom="Animalia" order="Ammonoidea" pageId="29" pageNumber="30" phylum="Mollusca" rank="species" species="meeki">
|
||
<emphasis id="B966EAA01510FF9EFDAEFC6AFCB68D8D" box="[563,780,917,938]" italics="true" pageId="29" pageNumber="30">Placenticeras meeki</emphasis>
|
||
<bibRefCitation id="EF834B431510FF9EFC8AFC6AFC1A8D8D" author="Bohm, J." box="[791,928,917,938]" pageId="29" pageNumber="30" pagination="183 - 201" refId="ref18246" refString="Bohm, J. 1898. Uber Ammonites pedernalis v. Buch. Zeitschrift der Deutschen Geologischen Gesellschaft 50: 183 - 201." type="journal article" year="1898">Böhm, 1898</bibRefCitation>
|
||
</taxonomicName>
|
||
, or
|
||
<taxonomicName id="4C124D311510FF9EFC4CFC6AFF448DE2" authority="Hyatt, 1903" authorityName=", Hyatt" authorityYear="1903" class="Cephalopoda" family="Placenticeratidae" genus="Placenticeras" kingdom="Animalia" order="Ammonoidea" pageId="29" pageNumber="30" phylum="Mollusca" rank="species" species="costatum">
|
||
<emphasis id="B966EAA01510FF9EFC4CFC6AFB718D8D" box="[977,1227,917,938]" italics="true" pageId="29" pageNumber="30">Placenticeras costatum</emphasis>
|
||
Hyatt, 1903
|
||
</taxonomicName>
|
||
, 31.
|
||
<emphasis id="B966EAA01510FF9EFEDDFC50FEE38DE3" bold="true" box="[320,345,943,964]" pageId="29" pageNumber="30">A.</emphasis>
|
||
AMNH 47279,
|
||
<taxonomicName id="4C124D311510FF9EFD8EFC4FFBDD8DE2" authority="Zone, Bearpaw Shale, Travers Dam" authorityName="Zone, Bearpaw Shale, Travers Dam" box="[531,1127,944,965]" class="Cephalopoda" family="Baculitidae" genus="Baculites" kingdom="Animalia" order="Ammonoidea" pageId="29" pageNumber="30" phylum="Mollusca" rank="species" species="reesidei">
|
||
<emphasis id="B966EAA01510FF9EFD8EFC4FFD688DE2" box="[531,722,944,965]" italics="true" pageId="29" pageNumber="30">Baculites reesidei</emphasis>
|
||
Zone, Bearpaw Shale, Travers Dam
|
||
</taxonomicName>
|
||
, Alberta, Canada.
|
||
<emphasis id="B966EAA01510FF9EFF44FC35FF4A8DF8" bold="true" box="[217,240,970,991]" pageId="29" pageNumber="30">B.</emphasis>
|
||
AMNH 47278,
|
||
<taxonomicName id="4C124D311510FF9EFE3EFC35FC068DF8" authority="Zone, Bearpaw Shale, Welling" authorityName="Zone, Bearpaw Shale, Welling" box="[419,956,970,991]" class="Cephalopoda" family="Baculitidae" genus="Baculites" kingdom="Animalia" order="Ammonoidea" pageId="29" pageNumber="30" phylum="Mollusca" rank="species" species="cuneatus">
|
||
<emphasis id="B966EAA01510FF9EFE3EFC35FDD08DF8" box="[419,618,970,991]" italics="true" pageId="29" pageNumber="30">Baculites cuneatus</emphasis>
|
||
Zone, Bearpaw Shale, Welling
|
||
</taxonomicName>
|
||
, Alberta, Canada.
|
||
</paragraph>
|
||
</caption>
|
||
<paragraph id="8BAD36B21510FF9EFF05FB1EFE918BC4" blockId="29.[123,652,1044,1741]" pageId="29" pageNumber="30">Ridges and grooves are visible on the black layer on most of the left wing, and parallel the posterior margin, becoming coarser and more widely spaced posteriorly. The posterior onehalf of the wing also shows irregular bumps suggesting plastic deformation. The steinkern shows a fingerprintlike pattern, reflecting the texture of the overlying black material.</paragraph>
|
||
<paragraph id="8BAD36B21510FF9EFF05FA16FD558A87" blockId="29.[123,652,1044,1741]" lastBlockId="29.[699,1228,1044,1741]" pageId="29" pageNumber="30">
|
||
UMUT MM28897 is an isolated lower jaw preserved in a piece of calcareous concretion with plant and shell fragments (
|
||
<figureCitation id="13292A371510FF9EFE6EF9DBFD3C881C" box="[499,646,1572,1595]" captionStart="Fig" captionStartId="34.[150,188,1587,1608]" captionText="Fig. 26. Lower jaws attributed to Metaplacenticeras subtilistriatum (Jimbo, 1894), Hokkaido, Japan. A–D. UMUT MM28897. A. Ventral view, anterior end on left, showing undulations paralleling the posterior margin. B. Closeup of the anterior end. C. Right lateral view. D. Left lateral view. E–H. UMUT MM28896. E. Ventral view, anterior end on left. The right wing is crumpled. F. Closeup of the anterior area showing fragments of the calcitic plate (arrow). G. Right lateral view. H. Left lateral view. Scale bar 5 5 mm." pageId="29" pageNumber="30">figs. 26A–D</figureCitation>
|
||
,
|
||
<figureCitation id="13292A371510FF9EFFE6F9BEFF26887F" box="[123,156,1601,1624]" captionStart="Fig" captionStartId="35.[149,187,858,879]" captionTargetBox="[158,1194,187,838]" captionTargetId="figure-13@35.[158,1194,187,838]" captionTargetPageId="35" captionText="Fig. 28. Drawing of part of the anterior end of UMUT MM28897 (see fig. 26A–D) showing the ridges paralleling the posterior margin. Texture as defined in figures 4 and 27." figureDoi="http://doi.org/10.5281/zenodo.5383560" httpUri="https://zenodo.org/record/5383560/files/figure.png" pageId="29" pageNumber="30">28</figureCitation>
|
||
). It is
|
||
<quantity id="4CEA9B571510FF9EFF6EF9BEFEF0887F" box="[243,330,1601,1624]" metricMagnitude="-2" metricUnit="m" metricValue="1.7" pageId="29" pageNumber="30" unit="mm" value="17.0">17 mm</quantity>
|
||
long and the left wing is approximately
|
||
<quantity id="4CEA9B571510FF9EFEB3F9A1FECC8852" box="[302,374,1630,1653]" metricMagnitude="-3" metricUnit="m" metricValue="9.0" pageId="29" pageNumber="30" unit="mm" value="9.0">9 mm</quantity>
|
||
wide (W/L of the left wing 5 0.53). Most of the jaw is intact, but the posterior portion is crumpled and ragged. The jaw is composed of three layers: the steinkern, an overlying layer of coarsely crystalline black material, and a top layer of finely crystalline yellowish material (calcite, see below) in the form of two plates (aptychi).
|
||
</paragraph>
|
||
<paragraph id="8BAD36B21510FF9EFD45FB59FCF58897" blockId="29.[699,1228,1044,1741]" pageId="29" pageNumber="30">
|
||
The apex is pointed, and the anterior margin is slightly indented on each side. The apical angle is approximately 1208. The usual steplike feature near the anterior margin is not present and is presumably covered over. The apex shows a slit that extends approximately
|
||
<quantity id="4CEA9B571510FF9EFC88FAA9FCE18B4A" box="[789,859,1366,1389]" metricMagnitude="-3" metricUnit="m" metricValue="4.0" pageId="29" pageNumber="30" unit="mm" value="4.0">4 mm</quantity>
|
||
along the midline. This slit is filled in with matrix, but black material is visible underneath—at least, at the posterior end of the slit. A groove is present on the rest of the jaw and is partly lined with black material, indicating that the two wings are continuous across the groove. The two calcitic plates (aptychi) terminate at the midline in a welldefined beveled edge. Thus, the underlying black layer is continuous across the middle, whereas the overlying calcitic plates are separate.
|
||
</paragraph>
|
||
<paragraph id="8BAD36B21510FF9EFD45F949FB7188EA" blockId="29.[699,1228,1044,1741]" box="[728,1227,1718,1741]" pageId="29" pageNumber="30">The calcitic plates (aptychi) are ornament</paragraph>
|
||
<caption id="DF6D663A1513FF9DFF0BFA1EFCD1880B" ID-DOI="http://doi.org/10.5281/zenodo.5383554" ID-Zenodo-Dep="5383554" httpUri="https://zenodo.org/record/5383554/files/figure.png" pageId="30" pageNumber="31" startId="30.[150,188,1505,1526]" targetBox="[131,1225,193,1483]" targetPageId="30">
|
||
<paragraph id="8BAD36B21513FF9DFF0BFA1EFCD1880B" blockId="30.[124,1229,1505,1580]" pageId="30" pageNumber="31">
|
||
Fig. 24.
|
||
<taxonomicName id="4C124D311513FF9DFE9EFA1DFD3A8BD1" authority="Hyatt, 1903" authorityName=", Hyatt" authorityYear="1903" box="[259,640,1505,1527]" class="Cephalopoda" family="Placenticeratidae" genus="Placenticeras" kingdom="Animalia" order="Ammonoidea" pageId="30" pageNumber="31" phylum="Mollusca" rank="species" species="costatum">
|
||
<emphasis id="B966EAA01513FF9DFE9EFA1DFE428BD0" box="[259,504,1506,1527]" italics="true" pageId="30" pageNumber="31">Placenticeras costatum</emphasis>
|
||
Hyatt, 1903
|
||
</taxonomicName>
|
||
, with lower jaw (right arrow) in body chamber, USNM 529075, U.S. Geological Survey loc. D1353,
|
||
<taxonomicName id="4C124D311513FF9DFDE4FA03FB738836" authority="Zone, Pierre Shale, Grand County" authorityName="Zone, Pierre Shale, Grand County" box="[633,1225,1532,1553]" class="Cephalopoda" family="Baculitidae" genus="Baculites" kingdom="Animalia" order="Ammonoidea" pageId="30" pageNumber="31" phylum="Mollusca" rank="species" species="cuneatus">
|
||
<emphasis id="B966EAA01513FF9DFDE4FA03FCF98836" box="[633,835,1532,1553]" italics="true" pageId="30" pageNumber="31">Baculites cuneatus</emphasis>
|
||
Zone, Pierre Shale, Grand County
|
||
</taxonomicName>
|
||
, Colorado. The left arrow indicates the base of the body chamber, 31.
|
||
</paragraph>
|
||
</caption>
|
||
<caption id="DF6D663A1512FF9CFF08FBDBFB768A1E" ID-DOI="http://doi.org/10.5281/zenodo.5383556" ID-Zenodo-Dep="5383556" box="[149,1228,1060,1082]" httpUri="https://zenodo.org/record/5383556/files/figure.png" pageId="31" pageNumber="32" startId="31.[149,187,1060,1081]" targetBox="[126,1226,187,1037]" targetPageId="31">
|
||
<paragraph id="8BAD36B21512FF9CFF08FBDBFB768A1E" blockId="31.[123,1228,1060,1108]" box="[149,1228,1060,1082]" pageId="31" pageNumber="32">
|
||
Fig. 25. Closeup of the lower jaw of
|
||
<taxonomicName id="4C124D311512FF9CFDA0FBDAFC7B8A1E" authority=", Hyatt, 1903" authorityName=", Hyatt" authorityYear="1903" box="[573,961,1060,1082]" class="Cephalopoda" family="Placenticeratidae" genus="Placenticeras" kingdom="Animalia" order="Ammonoidea" pageId="31" pageNumber="32" phylum="Mollusca" rank="species" species="costatum">
|
||
<emphasis id="B966EAA01512FF9CFDA0FBDAFC898A1D" box="[573,819,1061,1082]" italics="true" pageId="31" pageNumber="32">Placenticeras costatum</emphasis>
|
||
, Hyatt, 1903
|
||
</taxonomicName>
|
||
, USNM 529075 (see fig.
|
||
</paragraph>
|
||
</caption>
|
||
<paragraph id="8BAD36B21512FF9CFFE6FBC0FCEC8A73" blockId="31.[123,1228,1060,1108]" box="[123,854,1087,1108]" pageId="31" pageNumber="32">
|
||
24), ventral view, anterior end on top, 33.
|
||
<emphasis id="B966EAA01512FF9CFDD3FBC0FDDD8A73" bold="true" box="[590,615,1087,1108]" pageId="31" pageNumber="32">A.</emphasis>
|
||
Uncoated.
|
||
<emphasis id="B966EAA01512FF9CFD79FBC0FD418A73" bold="true" box="[740,763,1087,1108]" pageId="31" pageNumber="32">B.</emphasis>
|
||
Coated.
|
||
</paragraph>
|
||
<paragraph id="8BAD36B21512FF9CFFE6FB6AFEFA8B5D" blockId="31.[123,651,1173,1402]" pageId="31" pageNumber="32">ed with ridges and grooves that parallel the posterior margin. The ornament becomes coarser, more irregular, and more widely spaced toward the posterior end. Longitudinal striations are also present. The underlying black layer shows the same ornament as the aptychi, but the longitudinal striations are more prominent.</paragraph>
|
||
<paragraph id="8BAD36B21512FF9CFF66FA60FDD08BF4" blockId="31.[156,618,1439,1491]" pageId="31" pageNumber="32">COMPOSITION AND MICROSTRUCTURE OF THE JAWS</paragraph>
|
||
<paragraph id="8BAD36B21512FF9CFF05FA16FE40887F" blockId="31.[123,651,1513,1741]" pageId="31" pageNumber="32">The lower jaws of placenticeratids consist of several layers. The same layers are probably present in the upper jaws, but there are not enough data to confirm this.</paragraph>
|
||
<paragraph id="8BAD36B21512FF9CFF05F9A1FBC28BDE" blockId="31.[123,651,1513,1741]" lastBlockId="31.[699,1228,1173,1741]" pageId="31" pageNumber="32">
|
||
The surface of the steinkerns of the lower jaws of AMNH 47275 and 47277 shows a network of small, irregular craters, each approximately
|
||
<quantity id="4CEA9B571512FF9CFE8FF949FED888EA" box="[274,354,1718,1741]" metricMagnitude="-2" metricUnit="m" metricValue="8.0" pageId="31" pageNumber="32" unit="mm" value="80.0">80 mm</quantity>
|
||
long (
|
||
<figureCitation id="13292A371512FF9CFE2FF949FD8488EA" box="[434,574,1718,1741]" captionStart="Fig" captionStartId="36.[150,188,1031,1052]" captionTargetBox="[128,1228,186,1011]" captionTargetId="figure-17@36.[128,1228,186,1011]" captionTargetPageId="36" captionText="Fig. 29. A,B. Calcitic layer on the ventral side of the outer lamella of the lower jaw of UMUT MM28896 (see figs. 26E–H, 27). A. The surface is marked with growth lines. B. Cross section of the calcitic layer with fibrous microstructure. C, D. Dorsal surface of the outer lamella of the lower jaw of AMNH 47277 (see figs. 6, 7). C. The surface exhibits a network of small irregular craters, perhaps reflecting the impression of beccublast cells. D. Closeup of C." figureDoi="http://doi.org/10.5281/zenodo.5383562" httpUri="https://zenodo.org/record/5383562/files/figure.png" pageId="31" pageNumber="32">fig. 29C, D</figureCitation>
|
||
). Tanabe and Fukuda (1983) noted a similar pattern on the dorsal surface of the outer lamella of the lower jaw of the Late Cretaceous ammonite
|
||
<taxonomicName id="4C124D311512FF9CFC86FB0FFC098B20" authorityName="de Grossouvre" authorityYear="1894" box="[795,947,1264,1287]" class="Cephalopoda" family="Gaudryceratidae" genus="Gaudryceras" kingdom="Animalia" order="Ammonoidea" pageId="31" pageNumber="32" phylum="Mollusca" rank="genus">
|
||
<emphasis id="B966EAA01512FF9CFC86FB0FFC098B20" box="[795,947,1264,1287]" italics="true" pageId="31" pageNumber="32">Gaudryceras</emphasis>
|
||
</taxonomicName>
|
||
. They interpreted this pattern as an impression of beccublast cells, which attach the jaws to the musculature (see Dilly and Nixon, 1976), as in the jaws of coleoids and modern
|
||
<taxonomicName id="4C124D311512FF9CFC20FA97FB9A8B58" authorityName="Linnaeus" authorityYear="1758" box="[957,1056,1384,1407]" class="Cephalopoda" family="Nautilidae" genus="Nautilus" kingdom="Animalia" order="Nautilida" pageId="31" pageNumber="32" phylum="Mollusca" rank="genus">
|
||
<emphasis id="B966EAA01512FF9CFC20FA97FB9A8B58" box="[957,1056,1384,1407]" italics="true" pageId="31" pageNumber="32">Nautilus</emphasis>
|
||
</taxonomicName>
|
||
. If the pattern in
|
||
<taxonomicName id="4C124D311512FF9CFD46FA78FCC18BB9" authorityName="Meek" authorityYear="1876" box="[731,891,1415,1438]" class="Cephalopoda" family="Placenticeratidae" genus="Placenticeras" kingdom="Animalia" order="Ammonoidea" pageId="31" pageNumber="32" phylum="Mollusca" rank="genus">
|
||
<emphasis id="B966EAA01512FF9CFD46FA78FCC18BB9" box="[731,891,1415,1438]" italics="true" pageId="31" pageNumber="32">Placenticeras</emphasis>
|
||
</taxonomicName>
|
||
also reflects the imprints of beccublast cells, it would imply that the dorsal surface of the outer lamella of the lower jaw was attached to the jaw muscles.
|
||
</paragraph>
|
||
<paragraph id="8BAD36B21512FFA3FD45F9FFFEFF8FC7" blockId="31.[699,1228,1173,1741]" lastBlockId="32.[124,653,193,1741]" lastPageId="32" lastPageNumber="33" pageId="31" pageNumber="32">The principle component of the placenticeratid lower jaws is coarsely crystalline black material with a honeycomblike texture. This material probably represents diagenetically altered chitin, which is very resistant to decay (Lehmann, l981; Kear et al., 1995). Xray diffraction analysis of samples of this material from AMNH 47275, UWO.KMC.100126, BHMNH 5456, and BHMNH 5454b indicates that it consists of magnesium enriched calcite and amorphous material (organic compounds). In addition, the sample from AMNH 47275 contains pyrite, and the sample from UWO.KMC. 100126 contains siderite and illite, which probably reflect the composition of errant pieces of matrix.</paragraph>
|
||
<paragraph id="8BAD36B2152DFFA3FF04FE19FD3E8D7A" blockId="32.[124,653,193,1741]" pageId="32" pageNumber="33">
|
||
The thickness of the coarsely crystalline black material varies on different parts of the lower jaw. It is thickest in the anterior region—for example, it is
|
||
<quantity id="4CEA9B57152DFFA3FE02FDC1FE408C72" box="[415,506,574,597]" metricMagnitude="-4" metricUnit="m" metricValue="3.0" pageId="32" pageNumber="33" unit="mm" value="0.3">0.3 mm</quantity>
|
||
thick at this point in AMNH 47277. However, no specimen is sufficiently well enough preserved to measure the thickness on the entire jaw. Compaction and exfoliation of the chitin after death have undoubtedly altered the original thickness of this layer. As a point of reference, the thickness of the lower jaw of
|
||
<taxonomicName id="4C124D31152DFFA3FFE1FCD6FD898D67" authority="Saunders, 1981" authorityName="Saunders" authorityYear="1981" box="[124,563,809,832]" class="Cephalopoda" family="Nautilidae" genus="Nautilus" kingdom="Animalia" order="Nautilida" pageId="32" pageNumber="33" phylum="Mollusca" rank="species" species="belauensis">
|
||
<emphasis id="B966EAA0152DFFA3FFE1FCD6FED28D67" box="[124,360,809,832]" italics="true" pageId="32" pageNumber="33">Nautilus belauensis</emphasis>
|
||
<bibRefCitation id="EF834B43152DFFA3FEEBFCD6FD898D67" author="Saunders, W. B." box="[374,563,809,832]" pageId="32" pageNumber="33" pagination="1 - 7" refId="ref19319" refString="Saunders, W. B. 1981. A new species of Nautilus from Palau. Veliger 24: 1 - 7." type="journal article" year="1981">Saunders, 1981</bibRefCitation>
|
||
</taxonomicName>
|
||
, is approximately
|
||
<quantity id="4CEA9B57152DFFA3FE8FFCB9FED48D7A" box="[274,366,838,861]" metricMagnitude="-4" metricUnit="m" metricValue="5.0" pageId="32" pageNumber="33" unit="mm" value="0.5">0.5 mm</quantity>
|
||
near the posterior end.
|
||
</paragraph>
|
||
<paragraph id="8BAD36B2152DFFA3FF04FC9BFF178AFC" blockId="32.[124,653,193,1741]" pageId="32" pageNumber="33">
|
||
Clear to yellowish crystals are commonly embedded in the interstices in the black material. These crystals also occur as elongate struts on each side of the central boss at the junction of the inner and outer lamellae in BHMNH 5456 (
|
||
<figureCitation id="13292A37152DFFA3FEA6FC09FE318A2A" box="[315,395,1014,1037]" captionStart="Fig" captionStartId="25.[149,187,1282,1303]" captionTargetBox="[122,1229,185,1261]" captionTargetId="figure-13@25.[122,1229,185,1261]" captionTargetPageId="25" captionText="Fig. 20. Lower jaw of Placenticeras meeki Böhm, 1898, or Placenticeras costatum Hyatt, 1903, BHMNH 5456, Baculites cuneatus Zone, Pierre Shale, Meade County, South Dakota, ventral view, anterior end on top. The upper arrow indicates the edge of the outer lamella. The lower arrow indicates the separation between the two lamellae, fortuitously exposed at a break in the jaw, 32.7." figureDoi="http://doi.org/10.5281/zenodo.5383544" httpUri="https://zenodo.org/record/5383544/files/figure.png" pageId="32" pageNumber="33">fig. 20</figureCitation>
|
||
). Analysis of this material indicates that it consists of calcite enriched in magnesium. The calcitic crystals embedded in the black material are probably diagenetic in origin. However, it is conceivable that the struts represent an original calcitic thickening in the apical region of the jaw.
|
||
</paragraph>
|
||
<paragraph id="8BAD36B2152DFFA3FF04FB1EFE06883A" blockId="32.[124,653,193,1741]" pageId="32" pageNumber="33">
|
||
In many specimens, there is a finely crystalline yellowish to golden material overlying the black layer. Xray diffraction analysis of a sample of this material from AMNH 47275 indicates the presence of calcite enriched in magnesium, organic compounds, and pyrite. This layer demarcates the junction between the inner and outer lamellae in AMNH 47277 (
|
||
<figureCitation id="13292A37152DFFA3FF18FA33FF728BC4" box="[133,200,1484,1507]" captionStart="Fig" captionStartId="11.[149,187,1569,1590]" captionTargetBox="[239,1112,186,1549]" captionTargetId="figure-11@11.[239,1112,186,1549]" captionTargetPageId="11" captionText="Fig. 7. Closeup of the anterior end of AMNH 47277 (see fig. 6). A. Coated. B. Uncoated. The arrow indicates the edge of the outer lamella, 33." figureDoi="http://doi.org/10.5281/zenodo.5383517" httpUri="https://zenodo.org/record/5383517/files/figure.png" pageId="32" pageNumber="33">fig. 7</figureCitation>
|
||
), suggesting that although it may be diagenetically altered, this layer actually represents an original deposit.
|
||
</paragraph>
|
||
<paragraph id="8BAD36B2152DFFA3FF04F9DBFC758C54" blockId="32.[124,653,193,1741]" lastBlockId="32.[700,1229,193,1741]" pageId="32" pageNumber="33">
|
||
A thin outer calcitic layer is present in the
|
||
<specimenCount id="9D14FD3B152DFFA3FFE1F9BEFE94887F" box="[124,302,1601,1624]" pageId="32" pageNumber="33" type="generic">two specimens</specimenCount>
|
||
of
|
||
<taxonomicName id="4C124D31152DFFA3FEC2F9BEFF5F8851" baseAuthorityName="Jimbo" baseAuthorityYear="1894" class="Cephalopoda" family="Placenticeratidae" genus="Metaplacenticeras" kingdom="Animalia" order="Ammonoidea" pageId="32" pageNumber="33" phylum="Mollusca" rank="species" species="subtilistriatum">
|
||
<emphasis id="B966EAA0152DFFA3FEC2F9BEFF5F8851" italics="true" pageId="32" pageNumber="33">Metaplacenticeras subtilistriatum</emphasis>
|
||
</taxonomicName>
|
||
. In UMUT MM28896, this layer is only
|
||
<quantity id="4CEA9B57152DFFA3FF27F983FF4188B4" box="[186,251,1660,1683]" metricMagnitude="-3" metricUnit="m" metricValue="8.0" pageId="32" pageNumber="33" unit="mm" value="8.0">8 mm</quantity>
|
||
thick and shows a fibrous microstructure (
|
||
<figureCitation id="13292A37152DFFA3FF6EF966FECE8897" box="[243,372,1689,1712]" captionStart="Fig" captionStartId="36.[150,188,1031,1052]" captionTargetBox="[128,1228,186,1011]" captionTargetId="figure-17@36.[128,1228,186,1011]" captionTargetPageId="36" captionText="Fig. 29. A,B. Calcitic layer on the ventral side of the outer lamella of the lower jaw of UMUT MM28896 (see figs. 26E–H, 27). A. The surface is marked with growth lines. B. Cross section of the calcitic layer with fibrous microstructure. C, D. Dorsal surface of the outer lamella of the lower jaw of AMNH 47277 (see figs. 6, 7). C. The surface exhibits a network of small irregular craters, perhaps reflecting the impression of beccublast cells. D. Closeup of C." figureDoi="http://doi.org/10.5281/zenodo.5383562" httpUri="https://zenodo.org/record/5383562/files/figure.png" pageId="32" pageNumber="33">fig. 29A,B</figureCitation>
|
||
). It is covered with fine ridges and grooves that parallel the posterior margin. Xray diffraction analysis of samples of this material from both specimens indicates that it consists of magnesium enriched calcite. In addition, the sample from UMUT MM28897 contains quartz, which probably reflects the composition of errant pieces of matrix. A crystalline layer also covers part of the right wing in BHMNH 5456 (
|
||
<figureCitation id="13292A37152DFFA3FBF3FE71FB058F82" box="[1134,1215,398,421]" captionStart="Fig" captionStartId="25.[149,187,1282,1303]" captionTargetBox="[122,1229,185,1261]" captionTargetId="figure-13@25.[122,1229,185,1261]" captionTargetPageId="25" captionText="Fig. 20. Lower jaw of Placenticeras meeki Böhm, 1898, or Placenticeras costatum Hyatt, 1903, BHMNH 5456, Baculites cuneatus Zone, Pierre Shale, Meade County, South Dakota, ventral view, anterior end on top. The upper arrow indicates the edge of the outer lamella. The lower arrow indicates the separation between the two lamellae, fortuitously exposed at a break in the jaw, 32.7." figureDoi="http://doi.org/10.5281/zenodo.5383544" httpUri="https://zenodo.org/record/5383544/files/figure.png" pageId="32" pageNumber="33">fig. 20</figureCitation>
|
||
). However, unlike the layer in
|
||
<taxonomicName id="4C124D31152DFFA3FB81FE53FD528FC7" baseAuthorityName="Jimbo" baseAuthorityYear="1894" class="Cephalopoda" family="Placenticeratidae" genus="Metaplacenticeras" kingdom="Animalia" order="Ammonoidea" pageId="32" pageNumber="33" phylum="Mollusca" rank="species" species="subtilistriatum">
|
||
<emphasis id="B966EAA0152DFFA3FB81FE53FD528FC7" italics="true" pageId="32" pageNumber="33">M. subtilistriatum</emphasis>
|
||
</taxonomicName>
|
||
, the layer in BHMNH 5456 is very thick (
|
||
<quantity id="4CEA9B57152DFFA3FD58FE19FC918FDA" box="[709,811,486,509]" metricMagnitude="-3" metricUnit="m" metricValue="1.2" pageId="32" pageNumber="33" unit="mm" value="1.2">1.2 mm</quantity>
|
||
), pockmarked due to weathering, and devoid of any morphological features. It probably represents a diagenetic deposit. Xray diffraction analysis of this layer reveals the presence of calcite.
|
||
</paragraph>
|
||
<paragraph id="8BAD36B2152DFFA3FD44FD86FC1C8A2A" blockId="32.[700,1229,193,1741]" pageId="32" pageNumber="33">
|
||
A calcitic layer comparable to that in
|
||
<taxonomicName id="4C124D31152DFFA3FB03FD86FCD58C89" authorityName="Spath" authorityYear="1926" class="Cephalopoda" family="Placenticeratidae" genus="Metaplacenticeras" kingdom="Animalia" order="Ammonoidea" pageId="32" pageNumber="33" phylum="Mollusca" rank="genus">
|
||
<emphasis id="B966EAA0152DFFA3FB03FD86FCD58C89" italics="true" pageId="32" pageNumber="33">Metaplacenticeras</emphasis>
|
||
</taxonomicName>
|
||
is absent in the
|
||
<taxonomicName id="4C124D31152DFFA3FBB0FD68FB778C89" authorityName="Meek" authorityYear="1876" box="[1069,1229,663,686]" class="Cephalopoda" family="Placenticeratidae" genus="Placenticeras" kingdom="Animalia" order="Ammonoidea" pageId="32" pageNumber="33" phylum="Mollusca" rank="genus">
|
||
<emphasis id="B966EAA0152DFFA3FBB0FD68FB778C89" box="[1069,1229,663,686]" italics="true" pageId="32" pageNumber="33">Placenticeras</emphasis>
|
||
</taxonomicName>
|
||
jaws from North America. Interestingly, the North American jaws sometimes occur in association with ammonite shells retaining their original aragonitic composition. Based on the differential solubility of calcite versus aragonite, one would have supposed that the aragonite would have dissolved before the calcite, a fact that is commonly cited in studies of ammonite jaws (
|
||
<bibRefCitation id="EF834B43152DFFA3FC43FC61FD418DF4" author="Morton, N. & M. Nixon" pageId="32" pageNumber="33" pagination="231 - 238" refId="ref19190" refString="Morton, N., and M. Nixon. 1987. Size and function of ammonite aptychi in comparison with buccal masses of modern cephalopods. Lethaia 20: 231 - 238." type="journal article" year="1987">Morton and Nixon, 1987</bibRefCitation>
|
||
). Thus, the absence of a calcitic layer in these jaws would suggest that such a layer never existed at all.
|
||
</paragraph>
|
||
<paragraph id="8BAD36B2152DFFA1FD44FBEBFEAA8AC0" blockId="32.[700,1229,193,1741]" lastBlockId="34.[124,653,1056,1255]" lastPageId="34" lastPageNumber="35" pageId="32" pageNumber="33">
|
||
We propose an alternative explanation, however. We suggest that a thin calcitic layer also covered the lower jaws of
|
||
<taxonomicName id="4C124D31152DFFA3FBB0FBB0FB778A41" authorityName="Meek" authorityYear="1876" box="[1069,1229,1103,1126]" class="Cephalopoda" family="Placenticeratidae" genus="Placenticeras" kingdom="Animalia" order="Ammonoidea" pageId="32" pageNumber="33" phylum="Mollusca" rank="genus">
|
||
<emphasis id="B966EAA0152DFFA3FBB0FBB0FB778A41" box="[1069,1229,1103,1126]" italics="true" pageId="32" pageNumber="33">Placenticeras</emphasis>
|
||
</taxonomicName>
|
||
from North America, but that this layer was simply not preserved. This argument is based on the close affinity of
|
||
<taxonomicName id="4C124D31152DFFA3FC68FB58FB778A99" authorityName="Spath" authorityYear="1926" box="[1013,1229,1191,1214]" class="Cephalopoda" family="Placenticeratidae" genus="Metaplacenticeras" kingdom="Animalia" order="Ammonoidea" pageId="32" pageNumber="33" phylum="Mollusca" rank="genus">
|
||
<emphasis id="B966EAA0152DFFA3FC68FB58FB778A99" box="[1013,1229,1191,1214]" italics="true" pageId="32" pageNumber="33">Metaplacenticeras</emphasis>
|
||
</taxonomicName>
|
||
and
|
||
<taxonomicName id="4C124D31152DFFA3FD68FB3BFC2F8AFC" authorityName="Meek" authorityYear="1876" box="[757,917,1220,1243]" class="Cephalopoda" family="Placenticeratidae" genus="Placenticeras" kingdom="Animalia" order="Ammonoidea" pageId="32" pageNumber="33" phylum="Mollusca" rank="genus">
|
||
<emphasis id="B966EAA0152DFFA3FD68FB3BFC2F8AFC" box="[757,917,1220,1243]" italics="true" pageId="32" pageNumber="33">Placenticeras</emphasis>
|
||
</taxonomicName>
|
||
, and homology with the lower jaws of closely related ammonites (see below). Judging from the jaws of
|
||
<taxonomicName id="4C124D31152DFFA3FBC4FB00FC9F8B14" baseAuthorityName="Jimbo" baseAuthorityYear="1894" class="Cephalopoda" family="Placenticeratidae" genus="Metaplacenticeras" kingdom="Animalia" order="Ammonoidea" pageId="32" pageNumber="33" phylum="Mollusca" rank="species" species="subtilistriatum">
|
||
<emphasis id="B966EAA0152DFFA3FBC4FB00FC9F8B14" italics="true" pageId="32" pageNumber="33">M. subtilistriatum</emphasis>
|
||
</taxonomicName>
|
||
, the calcitic layer in
|
||
<taxonomicName id="4C124D31152DFFA3FBB0FAE3FB778B14" authorityName="Meek" authorityYear="1876" box="[1069,1229,1308,1331]" class="Cephalopoda" family="Placenticeratidae" genus="Placenticeras" kingdom="Animalia" order="Ammonoidea" pageId="32" pageNumber="33" phylum="Mollusca" rank="genus">
|
||
<emphasis id="B966EAA0152DFFA3FBB0FAE3FB778B14" box="[1069,1229,1308,1331]" italics="true" pageId="32" pageNumber="33">Placenticeras</emphasis>
|
||
</taxonomicName>
|
||
would also have been very thin and fibrous, unlike the thick aragonitic layer of the outer shell. As a consequence, the calcitic layer of the lower jaw would have been very friable and easily broken. In addition, jaws, as internal structures embedded in the buccal bulb, experienced a different taphonomic history from that of the outer shell. The microenvironment created within the buccal bulb after death may have promoted local dissolution of the calcite compared with the conditions affecting the outer shell. Indeed, in their study of the lower jaws of scaphitid ammonites from the Upper Cretaceous Fox Hills Formation,
|
||
<bibRefCitation id="EF834B43152FFFA1FED8FBDFFF198A73" author="Landman, N. H. & K. M. Waage" pageId="34" pageNumber="35" pagination="1 - 257" refId="ref18883" refString="Landman, N. H., and K. M. Waage. 1993. Scaphitid ammonites of the Upper Cretaceous (Maastrichtian) Fox Hills Formation in South Dakota and Wyoming. Bulletin of the American Museum of Natural History 215: 1 - 257." type="journal article" year="1993">Landman and Waage (1993: 60)</bibRefCitation>
|
||
noted that ‘‘The calcitic layer is usually absent on even slightly weathered surfaces, and in freshly exposed specimens it may be partly or entirely absent as a result of removal prior to formation of the enclosing concretion.’’
|
||
</paragraph>
|
||
</subSubSection>
|
||
</treatment>
|
||
</document> |