513 lines
53 KiB
XML
513 lines
53 KiB
XML
<document ID-DOI="10.1098/rspb.2002.2279" ID-GBIF-Dataset="76c4435d-1232-4de2-be3a-1fd37c1d27ed" ID-PMC="PMC1691292" ID-PubMed="12713747" ID-Zenodo-Dep="3732504" checkinTime="1585501157249" checkinUser="jeremy" docAuthor="Ruxton, Graeme D. & Houston, David C." docDate="2003" docId="038EA030B24DFFB7FFBFFC9A088AFF1E" docLanguage="en" docName="RuxtonHouston2003TrexScavenger.pdf.imd" docOrigin="Proceedings of the Royal Society, Series B 270" docStyle="DocumentStyle{}" docTitle="Tyrannosaurus rex Osborn 1905" docType="treatment" docVersion="10" lastPageNumber="733" masterDocId="FFB7D848B24DFFB5FFDCFFBA0B50FFDA" masterDocTitle="Could Tyrannosaurus rex have been a scavenger rather than a predator? An energetics approach" masterLastPageNumber="733" masterPageNumber="731" pageNumber="731" updateTime="1668144142230" updateUser="ExternalLinkService">
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<mods:titleInfo>
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<mods:title>Could Tyrannosaurus rex have been a scavenger rather than a predator? An energetics approach</mods:title>
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</mods:titleInfo>
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<mods:name type="personal">
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<mods:role>
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<mods:roleTerm>Author</mods:roleTerm>
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<mods:namePart>Ruxton, Graeme D.</mods:namePart>
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<mods:name type="personal">
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<mods:role>
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<mods:roleTerm>Author</mods:roleTerm>
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<mods:namePart>Houston, David C.</mods:namePart>
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<mods:title>Proceedings of the Royal Society, Series B</mods:title>
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<mods:part>
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<mods:date>2003</mods:date>
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<mods:number>270</mods:number>
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<mods:identifier type="DOI">10.1098/rspb.2002.2279</mods:identifier>
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<treatment ID-DOI="http://doi.org/10.5281/zenodo.3812733" ID-GBIF-Taxon="163318838" ID-Zenodo-Dep="3812733" LSID="urn:lsid:plazi:treatment:038EA030B24DFFB7FFBFFC9A088AFF1E" httpUri="http://treatment.plazi.org/id/038EA030B24DFFB7FFBFFC9A088AFF1E" lastPageId="2" lastPageNumber="733" pageId="0" pageNumber="731">
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<subSubSection pageId="0" pageNumber="731" type="nomenclature">
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<paragraph blockId="0.[99,733,800,1250]" pageId="0" pageNumber="731">
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Whether
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<taxonomicName authorityName="Osborn" authorityYear="1905" box="[202,385,801,822]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="731" phylum="Chordata" rank="species" species="rex">
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<emphasis box="[202,385,801,822]" italics="true" pageId="0" pageNumber="731">Tyrannosaurus rex</emphasis>
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</taxonomicName>
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was likely to have found food primarily by predation or scavenging has been debated for close to a century without resolution (
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<bibRefCitation author="Erickson, G. M. & Van Kirk, S. D. & Su, J. & Levenston, M. E. & Caler, W. E. & Carter, D. R." box="[513,729,861,884]" journalOrPublisher="Nature" pageId="0" pageNumber="731" pagination="706 - 708" part="382" refId="ref2980" refString="Erickson, G. M., Van Kirk, S. D., Su, J., Levenston, M. E., Caler, W. E. & Carter, D. R. 1996 Bite-force estimation for Tyrannosaurus rex from tooth-marked bones. Nature 382, 706 - 708." title="Bite-force estimation for Tyrannosaurus rex from tooth-marked bones" type="journal article" year="1996">
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Erickson
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<emphasis box="[615,666,862,884]" italics="true" pageId="0" pageNumber="731">et al.</emphasis>
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1996
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</bibRefCitation>
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;
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<bibRefCitation author="Erickson, G. M." box="[99,263,892,914]" journalOrPublisher="Scient. Am." pageId="0" pageNumber="731" pagination="34 - 41" part="281" refId="ref2957" refString="Erickson, G. M. 1999 Breathing live into Tyrannosaurus rex. Scient. Am. 281, 34 - 41." title="Breathing live into Tyrannosaurus rex" type="journal article" year="1999">Erickson 1999</bibRefCitation>
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). Much of this debate has used arguments based on jaw morphology and dentition. Here, we use calculations of energy gains and losses to estimate the minimum carrion productivity an ecosystem must provide in order to support an obligate scavenger of the 6 tonne (6000 kg) mass of
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<taxonomicName authorityName="Osborn" authorityYear="1905" box="[308,370,1046,1067]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="731" phylum="Chordata" rank="species" species="rex">
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<emphasis box="[308,370,1046,1067]" italics="true" pageId="0" pageNumber="731">T. rex</emphasis>
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</taxonomicName>
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. Our estimates suggest that carrion productivity equivalent to the current Serengeti would have been sufficient to support such a scavenger. Hence, we argue on the basis of physiological ecology that
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<taxonomicName authorityName="Osborn" authorityYear="1905" box="[99,160,1168,1189]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="731" phylum="Chordata" rank="species" species="rex">
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<emphasis box="[99,160,1168,1189]" italics="true" pageId="0" pageNumber="731">T. rex</emphasis>
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</taxonomicName>
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need not have been an active predator and could have found sufficient food to support itself purely by scavenging.
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</paragraph>
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</subSubSection>
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<paragraph blockId="0.[99,283,1302,1326]" box="[99,283,1302,1326]" pageId="0" pageNumber="731">
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<heading allCaps="true" bold="true" box="[99,283,1302,1326]" centered="true" fontSize="9" level="0" pageId="0" pageNumber="731" reason="2">
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<emphasis bold="true" box="[99,283,1302,1326]" pageId="0" pageNumber="731">2. THE MODEL</emphasis>
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</heading>
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</paragraph>
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<paragraph blockId="0.[99,736,1350,1861]" pageId="0" pageNumber="731">
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Our hypothesis is that the key constraint for scavengers is generally their ability to find food items. This is in contrast to predators, where capturing rather than discovering prey is the key constraint, and herbivores, where processing consumed food is often the key restriction on energy gain rate. We assume that the scavenger spends a constant fraction (a) of its time searching for food items that are distributed with a constant uniform density (
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<emphasis box="[705,712,1564,1585]" italics="true" pageId="0" pageNumber="731">f</emphasis>
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). If, when active, the scavenger searches out area at a rate
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<emphasis box="[99,117,1626,1647]" italics="true" pageId="0" pageNumber="731">V</emphasis>
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, then it finds food items at a rate a
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<emphasis box="[515,543,1625,1646]" italics="true" pageId="0" pageNumber="731">fV</emphasis>
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. We assume that it extracts an amount of energy
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<emphasis box="[472,488,1656,1677]" italics="true" pageId="0" pageNumber="731">E</emphasis>
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from each food item found. Hence, the rate of energy gathering (
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<emphasis box="[593,609,1687,1708]" italics="true" pageId="0" pageNumber="731">E</emphasis>
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<subScript attach="left" box="[609,621,1696,1709]" fontSize="6" pageId="0" pageNumber="731">in</subScript>
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) is a
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<emphasis box="[683,727,1686,1708]" italics="true" pageId="0" pageNumber="731">f VE</emphasis>
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. We assume that the individual has a resting metabolic rate
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<emphasis box="[99,116,1748,1769]" italics="true" pageId="0" pageNumber="731">R</emphasis>
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, but that searching for food requires extra energy investment at rate
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<emphasis box="[238,253,1778,1799]" italics="true" pageId="0" pageNumber="731">S</emphasis>
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. Thus, the rate of energy expenditure (
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<emphasis box="[685,701,1779,1800]" italics="true" pageId="0" pageNumber="731">E</emphasis>
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<subScript attach="left" box="[701,724,1787,1800]" fontSize="6" pageId="0" pageNumber="731">o ut</subScript>
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) is given by
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<emphasis box="[232,249,1809,1830]" italics="true" pageId="0" pageNumber="731">R</emphasis>
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+ a
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<emphasis box="[299,314,1809,1830]" italics="true" pageId="0" pageNumber="731">S</emphasis>
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, and scavengers attempt to optimize net energy gain (
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<emphasis box="[288,304,1840,1861]" italics="true" pageId="0" pageNumber="731">E</emphasis>
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<subScript attach="right" box="[305,328,1848,1861]" fontSize="6" pageId="0" pageNumber="731">net</subScript>
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) given by
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</paragraph>
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<paragraph blockId="0.[99,493,1883,1907]" box="[99,493,1883,1907]" pageId="0" pageNumber="731">
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<emphasis box="[99,115,1886,1907]" italics="true" pageId="0" pageNumber="731">E</emphasis>
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<subScript attach="left" box="[115,137,1894,1907]" fontSize="6" pageId="0" pageNumber="731">n et</subScript>
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=
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<emphasis box="[165,181,1886,1907]" italics="true" pageId="0" pageNumber="731">E</emphasis>
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<subScript attach="left" box="[182,194,1894,1907]" fontSize="6" pageId="0" pageNumber="731">in</subScript>
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‾
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<emphasis box="[230,246,1886,1907]" italics="true" pageId="0" pageNumber="731">E</emphasis>
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<subScript attach="left" box="[246,270,1894,1907]" fontSize="6" pageId="0" pageNumber="731">o ut</subScript>
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= a(
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<emphasis box="[329,376,1885,1907]" italics="true" pageId="0" pageNumber="731">f VE</emphasis>
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‾
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<emphasis box="[410,425,1886,1907]" italics="true" pageId="0" pageNumber="731">S</emphasis>
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) ‾
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<emphasis box="[468,485,1886,1907]" italics="true" pageId="0" pageNumber="731">R</emphasis>
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.
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</paragraph>
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<paragraph blockId="0.[680,735,1885,1907]" box="[680,735,1885,1907]" pageId="0" pageNumber="731">(2.1)</paragraph>
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<paragraph blockId="0.[99,728,1930,2059]" lastBlockId="0.[783,1412,754,838]" pageId="0" pageNumber="731">
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If we demand that
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<emphasis box="[328,344,1932,1953]" italics="true" pageId="0" pageNumber="731">E</emphasis>
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<subScript attach="left" box="[344,367,1940,1953]" fontSize="6" pageId="0" pageNumber="731">net</subScript>
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be positive then we can rearrange equation (2.1) as a restriction on the energy density of
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<subSubSection lastPageId="2" lastPageNumber="733" pageId="0" pageNumber="731" type="description">
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food available for scavenging: for a positive energy budget we demand that the density of food energy available to a scavenger is greater than a critical value given by
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<paragraph blockId="0.[788,963,863,921]" pageId="0" pageNumber="731">
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a
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<emphasis box="[889,904,866,887]" italics="true" pageId="0" pageNumber="731">S</emphasis>
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+
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<emphasis italics="true" pageId="0" pageNumber="731">R f E</emphasis>
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<subScript attach="left" box="[817,845,893,906]" fontSize="6" pageId="0" pageNumber="731">m in</subScript>
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=. a
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<emphasis box="[913,931,900,921]" italics="true" pageId="0" pageNumber="731">V</emphasis>
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</paragraph>
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<paragraph blockId="0.[1364,1419,883,905]" box="[1364,1419,883,905]" pageId="0" pageNumber="731">(2.2)</paragraph>
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<paragraph blockId="0.[783,1420,948,1276]" pageId="0" pageNumber="731">
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The right-hand side of this is the minimum energy density that an ecosystem needs to have to support a scavenger. We will now estimate this for a scavenging
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<taxonomicName authorityName="Osborn" authorityYear="1905" box="[1247,1310,1011,1032]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="731" phylum="Chordata" rank="species" species="rex">
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<emphasis box="[1247,1310,1011,1032]" italics="true" pageId="0" pageNumber="731">T. rex</emphasis>
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</taxonomicName>
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and compare this with the energy density of carrion in the extant Serengeti.
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</paragraph>
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<paragraph blockId="0.[783,1420,948,1276]" pageId="0" pageNumber="731">
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We will assume that restrictions owing to nightfall, bad weather and sleep mean that on average the scavenger can actively seek food for 50% of the 24 hour day, so we set a = 0.5. The relationship between the mass
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<emphasis box="[1268,1292,1194,1215]" italics="true" pageId="0" pageNumber="731">M</emphasis>
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of a reptile in kilograms and the resting metabolic rate
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<emphasis box="[1263,1280,1224,1245]" italics="true" pageId="0" pageNumber="731">R</emphasis>
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in watts has been described by
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<bibRefCitation author="Schmidt-Nielson, K." box="[993,1253,1254,1276]" journalOrPublisher="Cambridge University Press" pageId="0" pageNumber="731" refId="ref3318" refString="Schmidt-Nielson, K. 1984 Scaling: aehy is animal size so important? Cambridge University Press." title="Scaling: aehy is animal size so important?" type="book" year="1984">Schmidt-Nielson (1984)</bibRefCitation>
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</paragraph>
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<paragraph blockId="0.[783,941,1300,1325]" box="[783,941,1300,1325]" pageId="0" pageNumber="731">
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<emphasis box="[783,800,1304,1325]" italics="true" pageId="0" pageNumber="731">R</emphasis>
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= 0.38
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<emphasis box="[876,900,1304,1325]" italics="true" pageId="0" pageNumber="731">M</emphasis>
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0.83.
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</paragraph>
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<paragraph blockId="0.[1364,1419,1303,1325]" box="[1364,1419,1303,1325]" pageId="0" pageNumber="731">(2.3)</paragraph>
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<paragraph blockId="0.[783,1420,1352,1649]" pageId="0" pageNumber="731">
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There have been various estimates of the live mass of a full-sized
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<taxonomicName authorityName="Osborn" authorityYear="1905" box="[893,956,1384,1405]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="731" phylum="Chordata" rank="species" species="rex">
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<emphasis box="[893,956,1384,1405]" italics="true" pageId="0" pageNumber="731">T. rex</emphasis>
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</taxonomicName>
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, ranging from 3000 to 8000 kg (
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<bibRefCitation author="Farlow, J. O. & Smith, M. B. & Robinson, J. M." journalOrPublisher="J. Vertebrate Paleontol." pageId="0" pageNumber="731" pagination="713 - 725" part="15" refId="ref3111" refString="Farlow, J. O., Smith, M. B. & Robinson, J. M. 1995 Body mass, bone ' strength indicator ', and cursorial potential of Tyrannosaurus rex. J. Vertebrate Paleontol. 15, 713 - 725." title="Body mass, bone ' strength indicator ', and cursorial potential of Tyrannosaurus rex" type="journal article" year="1995">
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Farlow
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<emphasis box="[783,837,1414,1435]" italics="true" pageId="0" pageNumber="731">et al.</emphasis>
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1995
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</bibRefCitation>
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;
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<bibRefCitation author="Christiansen, P." box="[919,1123,1413,1435]" journalOrPublisher="Gaia" pageId="0" pageNumber="731" pagination="45 - 75" part="14" refId="ref2940" refString="Christiansen, P. 1997 Locomotion in sauropod dinosaurs. Gaia 14, 45 - 75." title="Locomotion in sauropod dinosaurs" type="journal article" year="1997">Christiansen 1997</bibRefCitation>
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;
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<bibRefCitation author="Seebacher, F." box="[1139,1321,1413,1435]" journalOrPublisher="J. Vertebrate Paleontol." pageId="0" pageNumber="731" pagination="51 - 60" part="21" refId="ref3336" refString="Seebacher, F. 2001 A new method to calculate allometric length-mass relationships in dinosaurs. J. Vertebrate Paleontol. 21, 51 - 60." title="A new method to calculate allometric length-mass relationships in dinosaurs" type="journal article" year="2001">Seebacher 2001</bibRefCitation>
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). Recent papers seem to be converging towards estimates close to 6 tonnes, so we will use a value of 6000 kg throughout this paper. Substituting this into equation (2.3) gives a value for
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<emphasis box="[822,839,1537,1558]" italics="true" pageId="0" pageNumber="731">R</emphasis>
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of 520 W. The relationship between the mass
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<emphasis box="[1364,1388,1537,1558]" italics="true" pageId="0" pageNumber="731">M</emphasis>
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of an ectotherm (in kg), the speed of travel
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<emphasis box="[1238,1251,1567,1588]" italics="true" pageId="0" pageNumber="731">v</emphasis>
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(in m s
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<superScript attach="left" box="[1337,1359,1563,1576]" fontSize="6" pageId="0" pageNumber="731">‾1</superScript>
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) and the extra cost of travel
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<emphasis box="[1052,1067,1597,1618]" italics="true" pageId="0" pageNumber="731">S</emphasis>
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(in W) has been suggested by
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<bibRefCitation author="Bennett, A. F." box="[783,952,1627,1649]" editor="C. Gans & F. H. Pough" journalOrPublisher="New York: Academic" pageId="0" pageNumber="731" pagination="155 - 199" refId="ref2819" refString="Bennett, A. F. 1982 The energetics of reptilian activity. In Biology of the reptilia, vol. 13 (ed. C. Gans & F. H. Pough), pp. 155 - 199. New York: Academic." title="The energetics of reptilian activity" type="book chapter" volumeTitle="Biology of the reptilia, vol. 13" year="1982">Bennett (1982)</bibRefCitation>
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to be
|
||
</paragraph>
|
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<paragraph blockId="0.[783,952,1673,1698]" box="[783,952,1673,1698]" pageId="0" pageNumber="731">
|
||
<emphasis box="[783,798,1677,1698]" italics="true" pageId="0" pageNumber="731">S</emphasis>
|
||
= 10.3
|
||
<emphasis box="[874,912,1677,1698]" italics="true" pageId="0" pageNumber="731">vM</emphasis>
|
||
<superScript attach="left" box="[911,943,1673,1686]" fontSize="6" pageId="0" pageNumber="731">0.64</superScript>
|
||
.
|
||
</paragraph>
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||
<paragraph blockId="0.[1364,1419,1676,1698]" box="[1364,1419,1676,1698]" pageId="0" pageNumber="731">(2.4)</paragraph>
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<paragraph blockId="0.[783,1418,1725,1900]" pageId="0" pageNumber="731">
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Reptiles can sustain a speed equivalent to 10% of their maximum speed (
|
||
<bibRefCitation author="Bennett, A. F. & Ruben, J. A." box="[979,1237,1756,1778]" journalOrPublisher="Science" pageId="0" pageNumber="731" pagination="649 - 654" part="206" refId="ref2866" refString="Bennett, A. F. & Ruben, J. A. 1979 Endothermy and activity in vertebrates. Science 206, 649 - 654." title="Endothermy and activity in vertebrates" type="journal article" year="1979">Bennett & Ruben 1979</bibRefCitation>
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||
). The maximum speed of equivalent-sized mammals and reptiles is similar (
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<bibRefCitation author="Bennett, A. F. & Ruben, J. A." box="[793,1081,1817,1839]" journalOrPublisher="Science" pageId="0" pageNumber="731" pagination="649 - 654" part="206" refId="ref2866" refString="Bennett, A. F. & Ruben, J. A. 1979 Endothermy and activity in vertebrates. Science 206, 649 - 654." title="Endothermy and activity in vertebrates" type="journal article" year="1979">Bennett & Ruben 1979</bibRefCitation>
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). The following relationship between mass
|
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<emphasis box="[952,976,1849,1870]" italics="true" pageId="0" pageNumber="731">M</emphasis>
|
||
(in kg) and maximum speed
|
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<emphasis box="[1331,1344,1849,1870]" italics="true" pageId="0" pageNumber="731">v</emphasis>
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<subScript attach="left" box="[1345,1374,1857,1870]" fontSize="6" pageId="0" pageNumber="731">m ax</subScript>
|
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(in m s
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<superScript attach="left" box="[821,843,1874,1887]" fontSize="6" pageId="0" pageNumber="731">‾1</superScript>
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) has been proposed by
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<bibRefCitation author="Alexander, R. McN" box="[1116,1308,1878,1900]" journalOrPublisher="J. Zool." pageId="0" pageNumber="731" pagination="125 - 146" part="183" refId="ref2735" refString="Alexander, R. McN. 1977 Allometry of the limbs of antelopes (Bovidea). J. Zool. 183, 125 - 146." title="Allometry of the limbs of antelopes (Bovidea)" type="journal article" year="1977">Alexander (1977)</bibRefCitation>
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:
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</paragraph>
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||
<paragraph blockId="0.[783,969,1924,1950]" box="[783,969,1924,1950]" pageId="0" pageNumber="731">
|
||
<emphasis box="[783,796,1929,1950]" italics="true" pageId="0" pageNumber="731">v</emphasis>
|
||
m ax = 8.5
|
||
<emphasis box="[890,914,1929,1950]" italics="true" pageId="0" pageNumber="731">M</emphasis>
|
||
‾ 0.08.
|
||
</paragraph>
|
||
<paragraph blockId="0.[1364,1419,1927,1949]" box="[1364,1419,1927,1949]" pageId="0" pageNumber="731">(2.5)</paragraph>
|
||
<paragraph blockId="0.[783,1420,1977,2061]" pageId="0" pageNumber="731">
|
||
Substituting
|
||
<emphasis box="[924,948,1978,1999]" italics="true" pageId="0" pageNumber="731">M</emphasis>
|
||
= 6000 in equation (2.5) gives a maximum speed for a
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[918,980,2009,2030]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="731" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[918,980,2009,2030]" italics="true" pageId="0" pageNumber="731">T. rex</emphasis>
|
||
</taxonomicName>
|
||
of 4.2 m s
|
||
<superScript attach="left" box="[1101,1124,2004,2017]" fontSize="6" pageId="0" pageNumber="731">‾ 1</superScript>
|
||
. This compares well with a recent estimate of 5 m s
|
||
<superScript attach="left" box="[1073,1095,2034,2047]" fontSize="6" pageId="0" pageNumber="731">‾1</superScript>
|
||
based on
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[1217,1279,2040,2061]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="0" pageNumber="731" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[1217,1279,2040,2061]" italics="true" pageId="0" pageNumber="731">T. rex</emphasis>
|
||
</taxonomicName>
|
||
’s limb mor-
|
||
</paragraph>
|
||
<footnote box="[99,570,2040,2059]" pageId="0" pageNumber="731">
|
||
<paragraph blockId="0.[99,728,1930,2059]" box="[99,570,2040,2059]" pageId="0" pageNumber="731">
|
||
<superScript attach="right" box="[99,109,2040,2050]" fontSize="4" pageId="0" pageNumber="731">*</superScript>
|
||
Author for correspondence (g.ruxton@bio.gla.ac.uk).
|
||
</paragraph>
|
||
</footnote>
|
||
<caption ID-DOI="http://doi.org/10.5281/zenodo.3961023" ID-Zenodo-Dep="3961023" httpUri="https://zenodo.org/record/3961023/files/figure.png" pageId="1" pageNumber="732" startId="1.[99,165,639,660]" targetBox="[91,745,117,616]" targetPageId="1">
|
||
<paragraph blockId="1.[99,730,639,801]" pageId="1" pageNumber="732">Figure 1. The minimum energy density that the ecosystem must provide to allow energy balance of the scavenger as a function of the distance in metres at which carrion can be detected, calculated from equation (2.7). The abscissa is logarithmic to the base 10 so ‘1’ represents 10 m, ‘2’ 100 m, ‘3’ 1 km and ‘4’ 10 km.</paragraph>
|
||
</caption>
|
||
<paragraph blockId="1.[99,736,870,1107]" pageId="1" pageNumber="732">
|
||
phology (
|
||
<bibRefCitation author="Hutchinson, J. R. & Garcia, M." box="[206,528,870,892]" journalOrPublisher="Nature" pageId="1" pageNumber="732" pagination="1018 - 1021" part="415" refId="ref3274" refString="Hutchinson, J. R. & Garcia, M. 2002 Tyrannosaurus was not a fast runner. Nature 415, 1018 - 1021." title="Tyrannosaurus was not a fast runner" type="journal article" year="2002">Hutchinson & Garcia 2002</bibRefCitation>
|
||
). We will assume that sustained travelling speed,
|
||
<emphasis box="[448,461,902,923]" italics="true" pageId="1" pageNumber="732">v</emphasis>
|
||
, is 10% of our estimate, i.e. 0.42 m s
|
||
<superScript attach="left" box="[235,258,928,941]" fontSize="6" pageId="1" pageNumber="732">‾ 1</superScript>
|
||
. If we substitute for
|
||
<emphasis box="[500,513,933,954]" italics="true" pageId="1" pageNumber="732">v</emphasis>
|
||
and
|
||
<emphasis box="[574,598,933,954]" italics="true" pageId="1" pageNumber="732">M</emphasis>
|
||
in equation (2.4), then this gives an added cost of travel
|
||
<emphasis box="[589,604,963,984]" italics="true" pageId="1" pageNumber="732">S</emphasis>
|
||
of 1100 W.
|
||
</paragraph>
|
||
<paragraph blockId="1.[99,736,870,1107]" pageId="1" pageNumber="732">
|
||
The rate at which an area is swept,
|
||
<emphasis box="[551,569,994,1015]" italics="true" pageId="1" pageNumber="732">V</emphasis>
|
||
, is simply the sustained travel speed
|
||
<emphasis box="[353,366,1024,1045]" italics="true" pageId="1" pageNumber="732">v</emphasis>
|
||
multiplied by twice the distance at which food can be detected, which we will denote
|
||
<emphasis box="[715,727,1055,1076]" italics="true" pageId="1" pageNumber="732">d</emphasis>
|
||
. That is
|
||
</paragraph>
|
||
<paragraph blockId="1.[99,212,1131,1153]" box="[99,212,1131,1153]" pageId="1" pageNumber="732">
|
||
<emphasis box="[99,117,1132,1153]" italics="true" pageId="1" pageNumber="732">V</emphasis>
|
||
= 0.84
|
||
<emphasis box="[192,204,1131,1152]" italics="true" pageId="1" pageNumber="732">d</emphasis>
|
||
.
|
||
</paragraph>
|
||
<paragraph blockId="1.[680,735,1131,1153]" box="[680,735,1131,1153]" pageId="1" pageNumber="732">(2.6)</paragraph>
|
||
<paragraph blockId="1.[99,727,1177,1322]" pageId="1" pageNumber="732">
|
||
Substituting the parameter values derived in equation (2.6) into equation (2.2) gives an equation for the minimum energy density of carrion (in J m
|
||
<superScript attach="right" box="[527,549,1235,1248]" fontSize="6" pageId="1" pageNumber="732">‾2</superScript>
|
||
) that could sustain an animal (
|
||
<emphasis box="[285,311,1270,1291]" italics="true" pageId="1" pageNumber="732">fE</emphasis>
|
||
<subScript attach="left" box="[312,339,1279,1292]" fontSize="6" pageId="1" pageNumber="732">m in</subScript>
|
||
) in terms of the distance at which it could detect carrion (
|
||
<emphasis box="[365,377,1300,1321]" italics="true" pageId="1" pageNumber="732">d</emphasis>
|
||
) as follows:
|
||
</paragraph>
|
||
<paragraph blockId="1.[104,251,1346,1402]" pageId="1" pageNumber="732">
|
||
2550
|
||
<emphasis box="[104,132,1365,1387]" italics="true" pageId="1" pageNumber="732">f E</emphasis>
|
||
<subScript attach="left" box="[133,160,1374,1387]" fontSize="6" pageId="1" pageNumber="732">m in</subScript>
|
||
=.
|
||
<emphasis box="[211,223,1381,1402]" italics="true" pageId="1" pageNumber="732">d</emphasis>
|
||
</paragraph>
|
||
<paragraph blockId="1.[680,734,1365,1387]" box="[680,734,1365,1387]" pageId="1" pageNumber="732">(2.7)</paragraph>
|
||
<paragraph blockId="1.[99,735,1427,2060]" pageId="1" pageNumber="732">
|
||
This relationship is plotted for a range of
|
||
<emphasis box="[581,593,1428,1449]" italics="true" pageId="1" pageNumber="732">d</emphasis>
|
||
values from 10 m to 10 km in
|
||
<figureCitation box="[300,386,1457,1479]" captionStart="Figure 1" captionStartId="1.[99,165,639,660]" captionTargetBox="[91,745,117,616]" captionTargetId="graphics@1.[185,733,141,561]" captionTargetPageId="1" captionText="Figure 1. The minimum energy density that the ecosystem must provide to allow energy balance of the scavenger as a function of the distance in metres at which carrion can be detected, calculated from equation (2.7). The abscissa is logarithmic to the base 10 so ‘1’ represents 10 m, ‘2’ 100 m, ‘3’ 1 km and ‘4’ 10 km." figureDoi="http://doi.org/10.5281/zenodo.3961023" httpUri="https://zenodo.org/record/3961023/files/figure.png" pageId="1" pageNumber="732">figure 1</figureCitation>
|
||
. To give us something to compare this against, we can estimate the energy density of carrion available each day from ungulate herbivores in the modern Serengeti ecosystem. It has been estimated that a total weight of 4´
|
||
<superScript attach="left" box="[332,340,1576,1589]" fontSize="6" pageId="1" pageNumber="732">107</superScript>
|
||
kg of ungulates die in the Serengeti each year (
|
||
<bibRefCitation author="Houston, D. C." box="[221,389,1610,1632]" editor="A. R. E. Sinclair & M. Norton-Griffiths" journalOrPublisher="Cambridge University Press" pageId="1" pageNumber="732" pagination="263 - 286" refId="ref3180" refString="Houston, D. C. 1979 The adaptations of scavengers. In Serengeti: dynamics of an ecosystem (ed. A. R. E. Sinclair & M. Norton-Griffiths), pp. 263 - 286. Cambridge University Press." title="The adaptations of scavengers" type="book chapter" volumeTitle="Serengeti: dynamics of an ecosystem" year="1979">Houston 1979</bibRefCitation>
|
||
). Assuming that these have an mass-specific energy content of 7´
|
||
<superScript attach="left" box="[559,567,1638,1651]" fontSize="6" pageId="1" pageNumber="732">106</superScript>
|
||
J kg
|
||
<superScript attach="left" box="[616,638,1638,1651]" fontSize="6" pageId="1" pageNumber="732">‾1</superScript>
|
||
(
|
||
<bibRefCitation author="Peters, R. H." journalOrPublisher="Cambridge University Press" pageId="1" pageNumber="732" refId="ref3300" refString="Peters, R. H. 1983 The ecological implications of body size. Cambridge University Press." title="The ecological implications of body size" type="book" year="1983">Peters 1983</bibRefCitation>
|
||
), and that the Serengeti stretches over 25 000 km
|
||
<superScript attach="right" box="[726,734,1668,1681]" fontSize="6" pageId="1" pageNumber="732">2</superScript>
|
||
(
|
||
<bibRefCitation author="Sinclair, A. R. E. & Norton-Griffiths, M." box="[106,493,1702,1724]" journalOrPublisher="Cambridge University Press" pageId="1" pageNumber="732" refId="ref3363" refString="Sinclair, A. R. E. & Norton-Griffiths, M. 1979 Serengeti: dynamics of an ecosystem. Cambridge University Press." title="Serengeti: dynamics of an ecosystem" type="book" year="1979">Sinclair & Norton-Griffiths 1979</bibRefCitation>
|
||
). This gives a mean energy density of 31 J m
|
||
<superScript attach="right" box="[379,402,1729,1742]" fontSize="6" pageId="1" pageNumber="732">‾ 2</superScript>
|
||
d
|
||
<superScript attach="left" box="[424,446,1729,1742]" fontSize="6" pageId="1" pageNumber="732">‾1</superScript>
|
||
. When we compare this value with
|
||
<figureCitation box="[221,306,1763,1785]" captionStart="Figure 1" captionStartId="1.[99,165,639,660]" captionTargetBox="[91,745,117,616]" captionTargetId="graphics@1.[185,733,141,561]" captionTargetPageId="1" captionText="Figure 1. The minimum energy density that the ecosystem must provide to allow energy balance of the scavenger as a function of the distance in metres at which carrion can be detected, calculated from equation (2.7). The abscissa is logarithmic to the base 10 so ‘1’ represents 10 m, ‘2’ 100 m, ‘3’ 1 km and ‘4’ 10 km." figureDoi="http://doi.org/10.5281/zenodo.3961023" httpUri="https://zenodo.org/record/3961023/files/figure.png" pageId="1" pageNumber="732">figure 1</figureCitation>
|
||
, we see that even if we make the conservative assumption that animals that die only remain available to
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[236,299,1825,1846]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="1" pageNumber="732" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[236,299,1825,1846]" italics="true" pageId="1" pageNumber="732">T. rex</emphasis>
|
||
</taxonomicName>
|
||
for 24 hours (before spoiling or being consumed by other scavengers), then, if it is able to monopolize all the food it finds and can detect food at a range of 80 m, an ecosystem of similar productivity to the current Serengeti would provide sufficient food for such a scavenger.
|
||
</paragraph>
|
||
<paragraph blockId="1.[99,735,1427,2060]" pageId="1" pageNumber="732">One reason for caution in the interpretation of our results is that the allometric relations used are based on</paragraph>
|
||
<paragraph blockId="1.[783,1414,143,410]" pageId="1" pageNumber="732">
|
||
data from extant reptiles, and consequently very few of the species used to generate the relations would have a mass approaching even 1% of our estimated mass for
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[783,844,236,257]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="1" pageNumber="732" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[783,844,236,257]" italics="true" pageId="1" pageNumber="732">T. rex</emphasis>
|
||
</taxonomicName>
|
||
. Of our estimates, the sustainable travel speed of 0.42 m s
|
||
<superScript attach="left" box="[876,899,262,275]" fontSize="6" pageId="1" pageNumber="732">‾ 1</superScript>
|
||
seems rather low for a bipedal animal with 2.5 m legs (see
|
||
<bibRefCitation author="Fitzgerald, R." box="[956,1149,296,318]" journalOrPublisher="Phys. Today" pageId="1" pageNumber="732" pagination="18 - 19" part="55" refId="ref3159" refString="Fitzgerald, R. 2002 How fast could Tyrannosaurus rex run? Phys. Today 55, 18 - 19." title="How fast could Tyrannosaurus rex run?" type="journal article" year="2002">Fitzgerald (2002)</bibRefCitation>
|
||
and references therein). If we repeat our calculations assuming a sustainable running speed of 2.1 m s
|
||
<superScript attach="right" box="[1047,1070,354,367]" fontSize="6" pageId="1" pageNumber="732">‾ 1</superScript>
|
||
, then this changes equation (2.7) to
|
||
</paragraph>
|
||
<paragraph blockId="1.[788,936,436,491]" pageId="1" pageNumber="732">
|
||
1600
|
||
<emphasis box="[788,817,454,476]" italics="true" pageId="1" pageNumber="732">f E</emphasis>
|
||
<subScript attach="left" box="[817,845,463,476]" fontSize="6" pageId="1" pageNumber="732">m in</subScript>
|
||
=.
|
||
<emphasis box="[895,907,470,491]" italics="true" pageId="1" pageNumber="732">d</emphasis>
|
||
</paragraph>
|
||
<paragraph blockId="1.[1364,1419,454,476]" box="[1364,1419,454,476]" pageId="1" pageNumber="732">(2.8)</paragraph>
|
||
<paragraph blockId="1.[783,1414,518,876]" pageId="1" pageNumber="732">The faster running speed increases the area that can be swept for food faster than it increases the total energetic requirements of that animal, and so this leads to a reduction in the food density required to sustain the scavenger. Thus, our initial assumption of a low running speed can be seen as conservative, making a scavenging lifestyle challenging to maintain.</paragraph>
|
||
<paragraph blockId="1.[783,1414,518,876]" pageId="1" pageNumber="732">
|
||
Some scientists consider that mammals (rather than reptiles) are a more appropriate model for dinosaurs (e.g.
|
||
<bibRefCitation author="Bakker, R. T." box="[783,933,792,814]" journalOrPublisher="New York: Citadel Press" pageId="1" pageNumber="732" refId="ref2762" refString="Bakker, R. T. 2001 The dinosaur heresies: neae theories unlocking the mystery of the dinosaurs. New York: Citadel Press." title="The dinosaur heresies: new theories unlocking the mystery of the dinosaurs" type="book" year="2001">Bakker 2001</bibRefCitation>
|
||
). It is possible to repeat our calculations under such an assumption.
|
||
<bibRefCitation author="Schmidt-Nielson, K." box="[1093,1363,823,845]" journalOrPublisher="Cambridge University Press" pageId="1" pageNumber="732" refId="ref3318" refString="Schmidt-Nielson, K. 1984 Scaling: aehy is animal size so important? Cambridge University Press." title="Scaling: aehy is animal size so important?" type="book" year="1984">Schmidt-Nielson (1984)</bibRefCitation>
|
||
suggests that this would change our equation for
|
||
<emphasis box="[1299,1316,855,876]" italics="true" pageId="1" pageNumber="732">R</emphasis>
|
||
to
|
||
</paragraph>
|
||
<paragraph blockId="1.[783,941,898,924]" box="[783,941,898,924]" pageId="1" pageNumber="732">
|
||
<emphasis box="[783,800,903,924]" italics="true" pageId="1" pageNumber="732">R</emphasis>
|
||
= 0.38
|
||
<emphasis box="[876,900,903,924]" italics="true" pageId="1" pageNumber="732">M</emphasis>
|
||
0.83,
|
||
</paragraph>
|
||
<paragraph blockId="1.[1364,1419,902,924]" box="[1364,1419,902,924]" pageId="1" pageNumber="732">(2.9)</paragraph>
|
||
<paragraph blockId="1.[783,1412,949,1032]" pageId="1" pageNumber="732">
|
||
increasing
|
||
<emphasis box="[901,918,950,971]" italics="true" pageId="1" pageNumber="732">R</emphasis>
|
||
substantially to 2300 W for our 6000 kg animal.
|
||
<bibRefCitation author="Calder III, W. A." box="[838,994,980,1002]" journalOrPublisher="New York: Dover Publications" pageId="1" pageNumber="732" refId="ref2918" refString="Calder III, W. A. 1996 Size, function, and life history. New York: Dover Publications." title="Size, function, and life history" type="book" year="1996">Calder (1996)</bibRefCitation>
|
||
suggests that, for a mammal, the equation for
|
||
<emphasis box="[887,902,1011,1032]" italics="true" pageId="1" pageNumber="732">S</emphasis>
|
||
becomes
|
||
</paragraph>
|
||
<paragraph blockId="1.[783,952,1055,1081]" box="[783,952,1055,1081]" pageId="1" pageNumber="732">
|
||
<emphasis box="[783,798,1059,1080]" italics="true" pageId="1" pageNumber="732">S</emphasis>
|
||
= 10.7
|
||
<emphasis box="[874,912,1060,1081]" italics="true" pageId="1" pageNumber="732">vM</emphasis>
|
||
<superScript attach="left" box="[911,943,1055,1068]" fontSize="6" pageId="1" pageNumber="732">0.68</superScript>
|
||
.
|
||
</paragraph>
|
||
<paragraph blockId="1.[1351,1419,1059,1081]" box="[1351,1419,1059,1081]" pageId="1" pageNumber="732">(2.10)</paragraph>
|
||
<paragraph blockId="1.[783,1410,1106,1251]" pageId="1" pageNumber="732">
|
||
<bibRefCitation author="Bennett, A. F. & Ruben, J. A." box="[783,1080,1106,1129]" journalOrPublisher="Science" pageId="1" pageNumber="732" pagination="649 - 654" part="206" refId="ref2866" refString="Bennett, A. F. & Ruben, J. A. 1979 Endothermy and activity in vertebrates. Science 206, 649 - 654." title="Endothermy and activity in vertebrates" type="journal article" year="1979">Bennett & Ruben (1979)</bibRefCitation>
|
||
suggest that the sustainable speed of mammals is 50% of their maximum speed, hence we will assume that
|
||
<emphasis box="[1019,1032,1169,1190]" italics="true" pageId="1" pageNumber="732">v</emphasis>
|
||
is 2.1 m s
|
||
<superScript attach="left" box="[1150,1172,1165,1178]" fontSize="6" pageId="1" pageNumber="732">‾1</superScript>
|
||
. If we finally assume that a is unchanged at 0.5, then (using mammals rather than reptiles as a model) changes equation (2.7) to
|
||
</paragraph>
|
||
<paragraph blockId="1.[788,936,1277,1332]" pageId="1" pageNumber="732">
|
||
3100
|
||
<emphasis box="[788,817,1295,1317]" italics="true" pageId="1" pageNumber="732">f E</emphasis>
|
||
<subScript attach="left" box="[817,845,1305,1318]" fontSize="6" pageId="1" pageNumber="732">m in</subScript>
|
||
=.
|
||
<emphasis box="[895,907,1311,1332]" italics="true" pageId="1" pageNumber="732">d</emphasis>
|
||
</paragraph>
|
||
<paragraph blockId="1.[1350,1418,1295,1317]" box="[1350,1418,1295,1317]" pageId="1" pageNumber="732">(2.11)</paragraph>
|
||
<paragraph blockId="1.[783,1419,1359,1564]" pageId="1" pageNumber="732">
|
||
Hence, we see that substantial compensation for higher resting and movement costs in a mammal-like
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[1304,1365,1391,1412]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="1" pageNumber="732" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[1304,1365,1391,1412]" italics="true" pageId="1" pageNumber="732">T. rex</emphasis>
|
||
</taxonomicName>
|
||
may come from a mammalian physiology allowing a higher sustainable rate of movement. The consequence of this is that the minimum food density required by our scavenger is only slightly increased if a mammalian model rather than a reptilian model is assumed.
|
||
</paragraph>
|
||
<paragraph blockId="1.[783,988,1622,1646]" box="[783,988,1622,1646]" pageId="1" pageNumber="732">
|
||
<heading allCaps="true" bold="true" box="[783,988,1622,1646]" fontSize="9" level="1" pageId="1" pageNumber="732" reason="2">
|
||
<emphasis bold="true" box="[783,988,1622,1646]" pageId="1" pageNumber="732">3. CONCLUSIONS</emphasis>
|
||
</heading>
|
||
</paragraph>
|
||
<paragraph blockId="1.[783,1414,1672,2060]" lastBlockId="2.[99,736,143,2021]" lastPageId="2" lastPageNumber="733" pageId="1" pageNumber="732">
|
||
Our calculation suggests that
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[1151,1212,1673,1694]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="1" pageNumber="732" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[1151,1212,1673,1694]" italics="true" pageId="1" pageNumber="732">T. rex</emphasis>
|
||
</taxonomicName>
|
||
would be able to gather enough food to survive as a pure scavenger if a number of conditions are met. One is that the ecosystem yields the same density of carrion as the current Serengeti. Estimates of primary productivity at the place and time appropriate to
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[956,1018,1825,1846]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="1" pageNumber="732" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[956,1018,1825,1846]" italics="true" pageId="1" pageNumber="732">T. rex</emphasis>
|
||
</taxonomicName>
|
||
vary widely but encompass values similar to that of the present-day Serengeti (
|
||
<bibRefCitation author="Beerling, D. J. & Woodward, F. I." journalOrPublisher="Cambridge University Press" pageId="1" pageNumber="732" refId="ref2788" refString="Beerling, D. J. & Woodward, F. I. 2001 Vegetation and the terrestrial carbon cycle: the first 400 million years. Cambridge University Press." title="Vegetation and the terrestrial carbon cycle: the first 400 million years" type="book" year="2001">Beerling & Woodward 2001</bibRefCitation>
|
||
). Any given primary productivity would have supported a greater biomass of ectothermic dinosaurs compared to the endothermic mammals that dominate the extant Serengeti (
|
||
<bibRefCitation author="Farlow, J. O." box="[978,1126,1977,1999]" editor="D. B. Weishampel & P. Dodson & H. Osmolska" journalOrPublisher="Berkeley, CA: University of California Press" pageId="1" pageNumber="732" pagination="43 - 55" refId="ref3037" refString="Farlow, J. O. 1990 Dinosaur energetics and thermal biology. In The Dinosauria (ed. D. B. Weishampel, P. Dodson & H. Osmolska), pp. 43 - 55. Berkeley, CA: University of California Press." title="Dinosaur energetics and thermal biology" type="book chapter" volumeTitle="The Dinosauria" year="1990">Farlow 1990</bibRefCitation>
|
||
). This higher biomass will more than compensate for the lower turnover rate per unit biomass that one would predict if dinosaurian herbivores had longer lifespans than the mammalian herbivores of the extant Serengeti, on account both of their larger size and probably lower specific metabolic rates.
|
||
</paragraph>
|
||
<paragraph blockId="2.[99,736,143,2021]" pageId="2" pageNumber="733">
|
||
Another condition is that
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[413,475,237,258]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[413,475,237,258]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
can detect carcasses at a distance of 80 m. Given the performance of polar bears in detecting seals over distances of kilometres (
|
||
<bibRefCitation author="Stirling, I." editor="G. L. Llano" journalOrPublisher="Houston, TX: Gulf Publishing Company" pageId="2" pageNumber="733" pagination="741 - 748" refId="ref3388" refString="Stirling, I. 1977 Polar bears. In Adaptations aeithin arctic ecosystems (ed. G. L. Llano), pp. 741 - 748. Houston, TX: Gulf Publishing Company." title="Polar bears" type="book chapter" volumeTitle="Adaptations aeithin arctic ecosystems" year="1977">Stirling 1977</bibRefCitation>
|
||
) and the ability of turkey vultures to find 80% of experimentally provided chicken carcasses in tropical rainforest within 12 hours of presentation (
|
||
<bibRefCitation author="Houston, D. C." journalOrPublisher="Condor" pageId="2" pageNumber="733" pagination="318 - 323" part="88" refId="ref3225" refString="Houston, D. C. 1986 Scavenging efficiency of turkey vultures in tropical forest. Condor 88, 318 - 323." title="Scavenging efficiency of turkey vultures in tropical forest" type="journal article" year="1986">Houston 1986</bibRefCitation>
|
||
), this seems likely to have been comfortably within
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[99,160,453,474]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[99,160,453,474]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
’s compass.
|
||
<bibRefCitation author="Brochu, C. A." box="[300,466,452,474]" journalOrPublisher="J. Vertebrate Paleontol." pageId="2" pageNumber="733" pagination="1 - 6" part="20" refId="ref2893" refString="Brochu, C. A. 2000 A digitally-rendered endocast for Tyrannosaurus rex. J. Vertebrate Paleontol. 20, 1 - 6." title="A digitally-rendered endocast for Tyrannosaurus rex" type="journal article" year="2000">Brochu (2000)</bibRefCitation>
|
||
argues, on the basis of computed tomographic analysis of a fossil skull, that
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[673,736,484,505]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[673,736,484,505]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
had greatly enlarged olfactory bulbs, suggestive of high olfactory acuity.
|
||
<bibRefCitation author="Farlow, J. O." box="[287,448,544,566]" journalOrPublisher="Hist. Biol." pageId="2" pageNumber="733" pagination="159 - 165" part="7" refId="ref3086" refString="Farlow, J. O. 1994 Speculations about the carrion-locating ability of Tyrannosaurs. Hist. Biol. 7, 159 - 165." title="Speculations about the carrion-locating ability of Tyrannosaurs" type="journal article" year="1994">Farlow (1994)</bibRefCitation>
|
||
suggests that the upright stance of
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[203,265,576,597]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[203,265,576,597]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
could have aided carrion location, both by visual and olfactory pathways.
|
||
</paragraph>
|
||
<paragraph blockId="2.[99,736,143,2021]" pageId="2" pageNumber="733">
|
||
We also assumed that the fallen carcass was only detectable to
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[189,251,669,690]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[189,251,669,690]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
for a period of 24 hours. Little is known about how long a carcass is accessible to vertebrate scavenges. Small (chicken) carcasses in tropical African forests were totally consumed by maggots within 3 days (
|
||
<bibRefCitation author="Houston, D. C." journalOrPublisher="Biotropica" pageId="2" pageNumber="733" pagination="376" part="19" refId="ref3248" refString="Houston, D. C. 1987 The effect of ant predation on carrion insect communities in a Brazilian forest. Biotropica 19, 376." title="The effect of ant predation on carrion insect communities in a Brazilian forest" type="journal article" year="1987">Houston 1987</bibRefCitation>
|
||
). Hence, our assumption that prey is only available for 1 day seems entirely reasonable, and if anything on the low side. Our final assumption that our focal
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[673,736,854,875]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[673,736,854,875]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
individual is able to find all the carcasses that fall in areas where it searches seems less plausible. It is likely that our
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[99,160,946,967]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[99,160,946,967]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
would experience competition from other species and from other members of its own species. However, if we arbitrarily assume that our focal individual is only able to access 25% of the carcasses that fall, so that the ecosystem has effectively only 25% of the carrion density of the Serengeti (7.75 J m
|
||
<superScript attach="right" box="[314,336,1096,1109]" fontSize="6" pageId="2" pageNumber="733">‾2</superScript>
|
||
), then (from
|
||
<figureCitation box="[498,584,1099,1121]" captionStart="Figure 1" captionStartId="1.[99,165,639,660]" captionTargetBox="[91,745,117,616]" captionTargetId="graphics@1.[185,733,141,561]" captionTargetPageId="1" captionText="Figure 1. The minimum energy density that the ecosystem must provide to allow energy balance of the scavenger as a function of the distance in metres at which carrion can be detected, calculated from equation (2.7). The abscissa is logarithmic to the base 10 so ‘1’ represents 10 m, ‘2’ 100 m, ‘3’ 1 km and ‘4’ 10 km." figureDoi="http://doi.org/10.5281/zenodo.3961023" httpUri="https://zenodo.org/record/3961023/files/figure.png" pageId="2" pageNumber="733">figure 1</figureCitation>
|
||
) we see that
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[99,160,1131,1152]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[99,160,1131,1152]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
would have to be able to detect prey at a distance of 330 m to balance its energy budget. This is more challenging, but still seems within the bounds of the possible, especially if, like many extant reptiles (
|
||
<bibRefCitation author="Zug, G. R. & Vitt, L. J. & Caldwell, J. P." box="[539,721,1222,1245]" journalOrPublisher="New York: Academic" pageId="2" pageNumber="733" refId="ref3425" refString="Zug, G. R., Vitt, L. J. & Caldwell, J. P. 2001 Herpetology: an introductory biology of amphibians and reptiles. New York: Academic." title="Herpetology: an introductory biology of amphibians and reptiles" type="book" year="2001">
|
||
Zug
|
||
<emphasis box="[598,653,1223,1245]" italics="true" pageId="2" pageNumber="733">et al.</emphasis>
|
||
2001
|
||
</bibRefCitation>
|
||
),
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[99,160,1254,1275]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[99,160,1254,1275]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
had an effective sense of smell. Hence, our conclusion is that an energy budget analysis suggests that a reptile as large as
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[292,354,1317,1338]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[292,354,1317,1338]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
could have survived using a purely scavenging lifestyle, providing that competition for carrion was low.
|
||
</paragraph>
|
||
<paragraph blockId="2.[99,736,143,2021]" pageId="2" pageNumber="733">
|
||
This conclusion leads to the obvious question, why is there not a
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[233,304,1441,1462]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[233,304,1441,1462]" italics="true" pageId="2" pageNumber="733">T. rex-</emphasis>
|
||
</taxonomicName>
|
||
like scavenger on the Serengeti today? Or generally, we must ask why vultures are the only extant vertebrates that have a predominantly scavenging lifestyle. The answer may be that an avian scavenger can outcompete a terrestrial one because, as mentioned in § 1, the key requirement for a scavenger is to minimize energy expenditure while searching. Compared to terrestrial locomotion, even powered flying is faster and much less energetically expensive per distance covered (Schmidt- Nielson 1984), and birds like vultures that make extensive use of soaring have dramatically lower energy expenditure than any terrestrial scavenger could have. If
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[601,663,1783,1804]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[601,663,1783,1804]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
was a scavenger, then this was probably only possible because avian radiation had yet to have a substantial effect on ecosystems.
|
||
</paragraph>
|
||
<paragraph blockId="2.[99,736,143,2021]" lastBlockId="2.[783,1412,143,271]" pageId="2" pageNumber="733">
|
||
It may well be, as suggested by
|
||
<bibRefCitation author="Farlow, J. O." box="[508,674,1906,1929]" journalOrPublisher="Hist. Biol." pageId="2" pageNumber="733" pagination="159 - 165" part="7" refId="ref3086" refString="Farlow, J. O. 1994 Speculations about the carrion-locating ability of Tyrannosaurs. Hist. Biol. 7, 159 - 165." title="Speculations about the carrion-locating ability of Tyrannosaurs" type="journal article" year="1994">Farlow (1994)</bibRefCitation>
|
||
, that
|
||
<taxonomicName authorityName="Osborn" authorityYear="1905" box="[99,160,1939,1960]" class="Reptilia" family="Tyrannosauridae" genus="Tyrannosaurus" higherTaxonomySource="GBIF" kingdom="Animalia" order="Dinosauria" pageId="2" pageNumber="733" phylum="Chordata" rank="species" species="rex">
|
||
<emphasis box="[99,160,1939,1960]" italics="true" pageId="2" pageNumber="733">T. rex</emphasis>
|
||
</taxonomicName>
|
||
was an opportunist flesh eater, combining scavenging carrion with active predation. That said, our calculations suggest that total (or near total) dependence on carrion (in the manner of extant vultures) may at least have been feasible.
|
||
</paragraph>
|
||
</subSubSection>
|
||
</paragraph>
|
||
</treatment>
|
||
</document> |