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src/main/resources/org/xmlcml/pdf2svg/Why sauropods had long necks; and why giraffes have short necks [PeerJ].htm

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+<title>Why sauropods had long necks; and why giraffes have short necks [PeerJ]</title>
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+                            <meta name="citation_title" content="Why sauropods had long necks; and why giraffes have short necks">
+                                <meta name="citation_date" content="2013-02-12">
+                                <meta name="citation_doi" content="10.7717/peerj.36">
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+                                <meta name="citation_authors" content="Taylor, Michael P.; Wedel, Mathew J.">
+                                <meta name="citation_author_institutions" content="Department of Earth Sciences, University of Bristol, Bristol, England; College of Osteopathic Medicine of the Pacific and College of Podiatric Medicine, Western University of Health Sciences, Pomona, California, USA">
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+    <meta name="description" content="The necks of the sauropod dinosaurs reached 15 m in length: six times longer than that of the world record giraffe and five times longer than those of all other terrestrial animals. Several anatomical features enabled this extreme elongation, including: absolutely large body size and quadrupedal stance providing a stable platform for a long neck; a small, light head that did not orally process food; cervical vertebrae that were both numerous and individually elongate; an efficient air-sac-based respiratory system; and distinctive cervical architecture. Relevant features of sauropod cervical vertebrae include: pneumatic chambers that enabled the bone to be positioned in a mechanically efficient way within the envelope; and muscular attachments of varying importance to the neural spines, epipophyses and cervical ribs. Other long-necked tetrapods lacked important features of sauropods, preventing the evolution of longer necks: for example, giraffes have relatively small torsos and large, heavy heads, share the usual mammalian constraint of only seven cervical vertebrae, and lack an air-sac system and pneumatic bones. Among non-sauropods, their saurischian relatives the theropod dinosaurs seem to have been best placed to evolve long necks, and indeed their necks probably surpassed those of giraffes. But 150 million years of evolution did not suffice for them to exceed a relatively modest 2.5 m.">
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+    <meta name="twitter:description" content="The necks of the sauropod dinosaurs reached 15 m in length: six times longer than that of the world record giraffe and five times longer than those of all other terrestrial animals. Several anatomical features enabled this extreme elongation, including: absolutely large body size and quadrupedal stance providing a stable platform for a long neck; a small, light head that did not orally process food; cervical vertebrae that were both numerous and individually elongate; an efficient air-sac-based respiratory system; and distinctive cervical architecture. Relevant features of sauropod cervical vertebrae include: pneumatic chambers that enabled the bone to be positioned in a mechanically efficient way within the envelope; and muscular attachments of varying importance to the neural spines, epipophyses and cervical ribs. Other long-necked tetrapods lacked important features of sauropods, preventing the evolution of longer necks: for example, giraffes have relatively small torsos and large, heavy heads, share the usual mammalian constraint of only seven cervical vertebrae, and lack an air-sac system and pneumatic bones. Among non-sauropods, their saurischian relatives the theropod dinosaurs seem to have been best placed to evolve long necks, and indeed their necks probably surpassed those of giraffes. But 150 million years of evolution did not suffice for them to exceed a relatively modest 2.5 m.">
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+  <header class="article-meta front">
+    <h1 class="article-title" itemprop="name">Why sauropods had long necks; and why giraffes have short necks</h1>
+    <div class="article-authors"><span class="contrib" id="author-1" data-jats-contrib-type="author"><a href="author-1" rel="author" itemprop="author"><span class="name"><span class="given-names">Michael P.</span> <span class="surname">Taylor</span></span></a><a class="xref corresp" href="mailto:dino@miketaylor.org.uk" target="_new" title="email the corresponding author" rel="tooltip"><i class="icon-envelope"> </i></a><sup class="contrib-xref-group"><a class="aff xref" href="#aff-1">1</a></sup></span>, <span class="contrib" id="author-2" data-jats-contrib-type="author"><a href="author-2" rel="author" itemprop="author"><span class="name"><span class="given-names">Mathew J.</span> <span class="surname">Wedel</span></span></a><sup class="contrib-xref-group"><a class="aff xref" href="#aff-2">2</a></sup></span></div>
+    <div id="article-information">
+      <div class="article-notes">
+        <div id="aff-1">
+          <span class="article-label-container">
+            <a class="article-label">1</a>
+          </span>
+          <span><span class="institution">Department of Earth Sciences</span>, <span class="addr-line">University of Bristol</span>, <span class="addr-line">Bristol</span>, <span class="country">England</span></span>
+        </div>
+        <div id="aff-2">
+          <span class="article-label-container">
+            <a class="article-label">2</a>
+          </span>
+          <span><span class="institution">College of Osteopathic Medicine of the Pacific and College of Podiatric Medicine</span>, <span class="addr-line">Western University of Health Sciences</span>, <span class="addr-line">Pomona, California</span>, <span class="country">USA</span></span>
+        </div>
+      </div>
+      <dl class="article-identifiers">
+        <dt> DOI</dt>
+        <dd>
+          <a href="http://dx.doi.org/10.7717/peerj.36" itemprop="identifier">10.7717/peerj.36</a>
+        </dd>
+      </dl>
+      <dl class="article-dates">
+        <dt>Published</dt>
+        <dd>
+          <time itemprop="datePublished">2013-02-12</time>
+        </dd>
+        <dt>Accepted</dt>
+        <dd>
+          <time itemprop="dateModified">2013-01-19</time>
+        </dd>
+        <dt>Received</dt>
+        <dd>
+          <time itemprop="dateCreated">2012-12-03</time>
+        </dd>
+      </dl>
+      <dl class="article-editors">
+        <dt>Academic Editor</dt>
+        <dd>
+          <a href="editor-1" class="contrib" id="editor-1" data-jats-contrib-type="editor">
+            <span class="name"><span class="given-names">John</span> <span class="surname">Hutchinson</span></span>
+          </a>
+        </dd>
+      </dl>
+      <dl class="article-subjects">
+        <dt>Subject Areas</dt>
+        <dd><a class="subject" itemprop="about" href="/search/?type=articles&amp;filter=Evolutionary Studies">Evolutionary Studies</a>, <a class="subject" itemprop="about" href="/search/?type=articles&amp;filter=Paleontology">Paleontology</a>, <a class="subject" itemprop="about" href="/search/?type=articles&amp;filter=Zoology">Zoology</a></dd>
+        <dt>Keywords</dt>
+        <dd><span class="kwd" itemprop="keywords">Sauropod</span>, <span class="kwd" itemprop="keywords">Giraffe</span>, <span class="kwd" itemprop="keywords">Dinosaur</span>, <span class="kwd" itemprop="keywords">Evolution</span>, <span class="kwd" itemprop="keywords">Cervical vertebra</span>, <span class="kwd" itemprop="keywords">Neck</span></dd>
+      </dl>
+      <dl class="article-license">
+        <dt>Copyright</dt>
+        <dd>© <span itemprop="copyrightYear">2013</span> <span itemprop="copyrightHolder">Taylor and Wedel</span></dd>
+        <dt>Licence</dt>
+        <dd>
+          <span class="license-p">This is an open access article distributed under the terms of the <a class="ext-link" href="http://creativecommons.org/licenses/by/3.0/" rel="license" data-jats-ext-link-type="uri">Creative Commons Attribution License</a>, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.</span>
+        </dd>
+      </dl>
+      <dl class="self-citation">
+        <dt>Cite this article</dt>
+        <dd><span class="self-citation-author-year">Taylor et al.</span> (<span class="self-citation-year">2013</span>) <span class="self-citation-title">Why sauropods had long necks; and why giraffes have short necks</span>. <span class="self-citation-journal" itemprop="publisher">PeerJ</span> <span class="self-citation-volume">1</span>:<span class="self-citation-elocation">e36</span> <a href="http://dx.doi.org/10.7717/peerj.36" itemprop="url">http://dx.doi.org/10.7717/peerj.36</a></dd>
+      </dl>
+      <div class="alert alert-success view-public-reviews">The authors have chosen to make <a href="/reviews/36/">the review history of this article</a> public.</div>
+    </div>
+    <div>
+      <h2>Abstract</h2>
+      <div class="abstract" itemprop="description">
+        <p>The necks of the sauropod dinosaurs reached 15 m in length: six times longer than that of the world record giraffe and five times longer than those of all other terrestrial animals. Several anatomical features enabled this extreme elongation, including: absolutely large body size and quadrupedal stance providing a stable platform for a long neck; a small, light head that did not orally process food; cervical vertebrae that were both numerous and individually elongate; an efficient air-sac-based respiratory system; and distinctive cervical architecture. Relevant features of sauropod cervical vertebrae include: pneumatic chambers that enabled the bone to be positioned in a mechanically efficient way within the envelope; and muscular attachments of varying importance to the neural spines, epipophyses and cervical ribs. Other long-necked tetrapods lacked important features of sauropods, preventing the evolution of longer necks: for example, giraffes have relatively small torsos and large, heavy heads, share the usual mammalian constraint of only seven cervical vertebrae, and lack an air-sac system and pneumatic bones. Among non-sauropods, their saurischian relatives the theropod dinosaurs seem to have been best placed to evolve long necks, and indeed their necks probably surpassed those of giraffes. But 150 million years of evolution did not suffice for them to exceed a relatively modest 2.5 m.</p>
+      </div>
+    </div>
+  </header>
+  <main>
+    <div class="body" lang="en">
+      <section class="sec" id="intro">
+        <h2 class="heading">Introduction</h2>
+        <p>Neck elongation occurs in many extant clades and is also found in many extinct groups. Some modern birds and certain extinct tetrapods have necks that are relatively long (i.e. as a proportion of total body length). Although these are interesting modifications of the basic tetrapod body plan, here we are concerned with absolute neck length. This is of interest because of the great mechanical difficulties imposed by absolutely long necks, and the anatomical novelties that needed to evolve to make such necks possible.</p>
+        <p>The necks of the sauropod dinosaurs were by far the longest of any animal, six times longer than that of the world record giraffe and five times longer than those of all other terrestrial animals. In many long-necked animals, the legs are of a similar length and so the neck elongation can be explained as a simple consequence of the need to reach down to ground level – for example in order to drink. By contrast, the necks of all sauropods were longer than necessary to reach the ground – in most cases, many times longer.</p>
+        <p>We survey the evolutionary history of long necks in sauropods and other animals, and consider the factors that allowed sauropod necks to grow so long. We then examine the osteology of sauropod necks more closely, comparing their cervical anatomy with that of their nearest extant relatives, the birds and crocodilians, and discussing unusual features of sauropods’ cervical vertebrae. Finally we discuss which neck elongation features were absent in non-sauropods, and show why giraffes have such short necks.</p>
+      </section>
+      <section class="sec">
+        <h2 class="heading">Long Necks in Different Taxa</h2>
+        <p>While they reach their zenith in sauropods, long necks have evolved repeatedly in several different groups of tetrapods. Long necks impose a high structural and metabolic cost, but provide evolutionary advantages including an increased browsing range (<cite itemprop="citation" itemscope="itemscope" itemref="ref-19" data-jats-ref-type="bibr" data-jats-rid="ref-19" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1086/509940" title="Winning by a neck: tall giraffes avoid competing with shorter browsers" data-jats-ref-type="bibr" data-jats-rid="ref-19">Cameron &amp; du Toit, 2007</a></cite>) and the ability to graze a wide area without locomotion (<cite itemprop="citation" itemscope="itemscope" itemref="ref-85" data-jats-ref-type="bibr" data-jats-rid="ref-85" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Mobility and feeding of Cetiosaurus (saurischia, sauropoda) – why the long neck?&quot;" title="Mobility and feeding of Cetiosaurus (saurischia, sauropoda) – why the long neck?" data-jats-ref-type="bibr" data-jats-rid="ref-85">Martin, 1987</a></cite>) and probably played some role in mate attraction (<cite itemprop="citation" itemscope="itemscope" itemref="ref-126" data-jats-ref-type="bibr" data-jats-rid="ref-126" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1086/285955" title="Winning by a neck: sexual selection in the evolution of giraffe" data-jats-ref-type="bibr" data-jats-rid="ref-126">Simmons &amp; Scheepers, 1996</a></cite>; <cite itemprop="citation" itemscope="itemscope" itemref="ref-123" data-jats-ref-type="bibr" data-jats-rid="ref-123" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1111/j.1469-7998.2006.00197.x" title="Necks for sex: sexual selection as an explanation for sauropod dinosaur neck elongation" data-jats-ref-type="bibr" data-jats-rid="ref-123">Senter, 2006</a></cite>; <cite itemprop="citation" itemscope="itemscope" itemref="ref-132" data-jats-ref-type="bibr" data-jats-rid="ref-132" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1111/j.1469-7998.2011.00824.x" title="The long necks of sauropods did not evolve primarily through sexual selection" data-jats-ref-type="bibr" data-jats-rid="ref-132">Taylor et al., 2011</a></cite>). Here we survey the longest necked taxa in several groups of extant and extinct animals (<a class="xref xref-fig" href="#fig-1" data-jats-ref-type="fig" data-jats-rid="fig-1">Figs. 1</a> and <a class="xref xref-fig" href="#fig-2" data-jats-ref-type="fig" data-jats-rid="fig-2">2</a>).</p>
+        <figure class="fig" id="fig-1">
+          <div class="image-container">
+            <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-1-2x.jpg" title="View the full image" class="fresco" data-fresco-caption="Figure 1: Necks of long-necked non-sauropods, to scale." data-fresco-group="figure" data-fresco-options="fit: 'width', ui: 'outside', thumbnails: false, loop: true, position: true, preload: false">
+              <img class="graphic" src="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-1-1x.jpg" data-image-id="fig-1" alt="Necks of long-necked non-sauropods, to scale." data-full="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-1-full.png" data-thumb="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-1-thumb.jpg" data-original="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-1.png" data-image-type="figure" data-jats-mimetype="image" data-jats-mime-subtype="png"/>
+            </a>
+          </div>
+          <figcaption>
+            <h3 class="heading"><span class="caption-label">Figure 1: </span>Necks of long-necked non-sauropods, to scale.</h3>
+            <span class="p">The giraffe and <i>Paraceratherium</i> are the longest necked mammals; the ostrich is the longest necked extant bird; <i>Therizinosaurus</i> and <i>Gigantoraptor</i> are the largest representatives of two long-necked theropod clades; <i>Arambourgiania</i> is the longest necked pterosaur; and <i>Tanystropheus</i> has a uniquely long neck relative to torso length. Human head modified from Gray’s Anatomy (1918 edition, fig. 602). Giraffe modified from photograph by Kevin Ryder (CC BY, <a class="uri" href="http://flic.kr/p/cRvCcQ">http://flic.kr/p/cRvCcQ</a>). Ostrich modified from photograph by “kei51” (CC BY, <a class="uri" href="http://flic.kr/p/cowoYW">http://flic.kr/p/cowoYW</a>). <i>Paraceratherium</i> modified from <cite itemprop="citation" itemscope="itemscope" itemref="ref-103" data-jats-ref-type="bibr" data-jats-rid="ref-103" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Baluchitherium grangeri, a giant hornless rhinoceros from Mongolia&quot;" title="Baluchitherium grangeri, a giant hornless rhinoceros from Mongolia" data-jats-ref-type="bibr" data-jats-rid="ref-103">Osborn</a></cite> (<cite itemprop="citation" itemscope="itemscope" itemref="ref-103" data-jats-ref-type="bibr" data-jats-rid="ref-103" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Baluchitherium grangeri, a giant hornless rhinoceros from Mongolia&quot;" title="Baluchitherium grangeri, a giant hornless rhinoceros from Mongolia" data-jats-ref-type="bibr" data-jats-rid="ref-103">1923</a></cite>, figure 1). <i>Therizinosaurus</i> modified from <i>Nothronychus</i> reconstruction by Scott Hartman. <i>Gigantoraptor</i> modified from <i>Heyuannia</i> reconstruction by Scott Hartman. <i>Arambourgiania</i> modified from <i>Zhejiangopterus</i> reconstruction by <cite itemprop="citation" itemscope="itemscope" itemref="ref-154" data-jats-ref-type="bibr" data-jats-rid="ref-154" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1371/journal.pone.000227" title="A reappraisal of azhdarchid pterosaur functional morphology and paleoecology" data-jats-ref-type="bibr" data-jats-rid="ref-154">Witton &amp; Naish (2008, figure 1)</a></cite>. <i>Tanystropheus</i> modified from reconstruction by David Peters. Alternating blue and pink bars are 1 m tall.</span>
+            <div class="article-image-download">
+              <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-1-full.png" class="btn btn-mini" download="peerj-36-fig-1.png"><i class="icon-picture"> </i> Download full-size image</a>
+            </div>
+            <div class="object-id article-component-doi">DOI: <a href="http://dx.doi.org/10.7717/peerj.36/fig-1" rel="tooltip" title="Cite this object using this DOI">10.7717/peerj.36/fig-1</a></div>
+          </figcaption>
+        </figure>
+        <figure class="fig" id="fig-2">
+          <div class="image-container">
+            <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-2-2x.jpg" title="View the full image" class="fresco" data-fresco-caption="Figure 2: Full skeletal reconstructions of selected long-necked non-sauropods, to scale." data-fresco-group="figure" data-fresco-options="fit: 'width', ui: 'outside', thumbnails: false, loop: true, position: true, preload: false">
+              <img class="graphic" src="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-2-1x.jpg" data-image-id="fig-2" alt="Full skeletal reconstructions of selected long-necked non-sauropods, to scale." data-full="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-2-full.png" data-thumb="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-2-thumb.jpg" data-original="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-2.png" data-image-type="figure" data-jats-mimetype="image" data-jats-mime-subtype="png"/>
+            </a>
+          </div>
+          <figcaption>
+            <h3 class="heading"><span class="caption-label">Figure 2: </span>Full skeletal reconstructions of selected long-necked non-sauropods, to scale.</h3>
+            <span class="p">1, <i>Paraceratherium.</i> 2, <i>Therizinosaurus.</i> 3, <i>Gigantoraptor.</i> 4, <i>Elasmosaurus.</i> 5, <i>Tanystropheus</i>. <i>Elasmosaurus</i> modified from <cite itemprop="citation" itemscope="itemscope" itemref="ref-26" data-jats-ref-type="bibr" data-jats-rid="ref-26" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;On Elasmosaurus platyurus Cope&quot;" title="On Elasmosaurus platyurus Cope" data-jats-ref-type="bibr" data-jats-rid="ref-26">Cope (1870, plate II, figure 1)</a></cite>. Other image sources as for <a class="xref xref-fig" href="#fig-1" data-jats-ref-type="fig" data-jats-rid="fig-1">Fig. 1</a>. Scale bar = 2 m.</span>
+            <div class="article-image-download">
+              <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-2-full.png" class="btn btn-mini" download="peerj-36-fig-2.png"><i class="icon-picture"> </i> Download full-size image</a>
+            </div>
+            <div class="object-id article-component-doi">DOI: <a href="http://dx.doi.org/10.7717/peerj.36/fig-2" rel="tooltip" title="Cite this object using this DOI">10.7717/peerj.36/fig-2</a></div>
+          </figcaption>
+        </figure>
+        <p>Note that most of the length estimates in this section are necessarily imprecise, being based on incomplete specimens and cross-scaling assumptions. They can be taken only as indicative, not as reliable figures.</p>
+        <div class="table-wrap" id="table-1">
+          <div class="caption">
+            <span class="caption-label">Table 1: </span>
+            <span class="p">Neck statistics of some sauropods, chosen because of unusually long, short or complete necks.</span>
+          </div>
+          <div class="table-container">
+            <table>
+              <colgroup>
+                <col align="left"/>
+                <col align="left"/>
+                <col align="left"/>
+                <col align="left"/>
+                <col align="left"/>
+                <col align="left"/>
+              </colgroup>
+              <thead>
+                <tr>
+                  <th style="text-align:left;">Taxon</th>
+                  <th style="text-align:left;">Neck length (m)</th>
+                  <th style="text-align:left;">Cervical count</th>
+                  <th style="text-align:left;">Longest centrum (cm)</th>
+                  <th style="text-align:left;">Longest cervical rib (cm)</th>
+                  <th style="text-align:left;">Maximum elongation index</th>
+                </tr>
+              </thead>
+              <tbody>
+                <tr>
+                  <td style="text-align:left;">
+                    <i>Mamenchisaurus hochuanensis</i>
+                  </td>
+                  <td style="text-align:left;">9.5</td>
+                  <td style="text-align:left;">19</td>
+                  <td style="text-align:left;">73  (C11)</td>
+                  <td style="text-align:left;">210 (C14)</td>
+                  <td style="text-align:left;">2.9  (C6)</td>
+                </tr>
+                <tr>
+                  <td style="text-align:left;">
+                    <i>Mamenchisaurus sinocanadorum</i>
+                  </td>
+                  <td style="text-align:left;">12 est.</td>
+                  <td style="text-align:left;">19?</td>
+                  <td style="text-align:left;"/>
+                  <td style="text-align:left;"> ≥ 410</td>
+                  <td style="text-align:left;"/>
+                </tr>
+                <tr>
+                  <td style="text-align:left;">
+                    <i>Brachytrachelopan mesai</i>
+                  </td>
+                  <td style="text-align:left;">1.1 est.</td>
+                  <td style="text-align:left;">12?</td>
+                  <td style="text-align:left;">10</td>
+                  <td style="text-align:left;"> ≤ centrum</td>
+                  <td style="text-align:left;"> ≤ 1</td>
+                </tr>
+                <tr>
+                  <td style="text-align:left;">
+                    <i>Apatosaurus louisae</i>
+                  </td>
+                  <td style="text-align:left;">5.9</td>
+                  <td style="text-align:left;">15</td>
+                  <td style="text-align:left;">55  (C11)</td>
+                  <td style="text-align:left;">39  (C11)</td>
+                  <td style="text-align:left;">3.7  (C4)</td>
+                </tr>
+                <tr>
+                  <td style="text-align:left;">
+                    <i>Diplodocus carnegii</i>
+                  </td>
+                  <td style="text-align:left;">6.5</td>
+                  <td style="text-align:left;">15</td>
+                  <td style="text-align:left;">64  (C14)</td>
+                  <td style="text-align:left;">48  (C11)</td>
+                  <td style="text-align:left;">4.9  (C7)</td>
+                </tr>
+                <tr>
+                  <td style="text-align:left;">
+                    <i>Barosaurus lentus</i>
+                  </td>
+                  <td style="text-align:left;">8.5 est.</td>
+                  <td style="text-align:left;">16?</td>
+                  <td style="text-align:left;">87  (C14)</td>
+                  <td style="text-align:left;">&lt;centrum</td>
+                  <td style="text-align:left;">5.4  (C8)</td>
+                </tr>
+                <tr>
+                  <td style="text-align:left;">
+                    <i>Supersaurus vivianae</i>
+                  </td>
+                  <td style="text-align:left;">15.0 est.</td>
+                  <td style="text-align:left;">15?</td>
+                  <td style="text-align:left;"> ≥ 138</td>
+                  <td style="text-align:left;"> ≤ centrum</td>
+                  <td style="text-align:left;"/>
+                </tr>
+                <tr>
+                  <td style="text-align:left;">
+                    <i>Giraffatitan brancai</i>
+                  </td>
+                  <td style="text-align:left;">8.5</td>
+                  <td style="text-align:left;">13</td>
+                  <td style="text-align:left;">100 (C10)</td>
+                  <td style="text-align:left;">290 (C7)</td>
+                  <td style="text-align:left;">5.4 (C5)</td>
+                </tr>
+                <tr>
+                  <td style="text-align:left;">
+                    <i>Sauroposeidon proteles</i>
+                  </td>
+                  <td style="text-align:left;">11.5 est.</td>
+                  <td style="text-align:left;">13?</td>
+                  <td style="text-align:left;">125 (C8)</td>
+                  <td style="text-align:left;">342 (C6)</td>
+                  <td style="text-align:left;">6.1 (C6)</td>
+                </tr>
+                <tr>
+                  <td style="text-align:left;">
+                    <i>Euhelopus zdanskyi</i>
+                  </td>
+                  <td style="text-align:left;">4.0</td>
+                  <td style="text-align:left;">17</td>
+                  <td style="text-align:left;">28  (C11)</td>
+                  <td style="text-align:left;">72  (C14)</td>
+                  <td style="text-align:left;">4.0 (C4)</td>
+                </tr>
+              </tbody>
+            </table>
+          </div>
+          <div class="object-id article-component-doi">DOI: <a href="http://dx.doi.org/10.7717/peerj.36/table-1" rel="tooltip" title="Cite this object using this DOI">10.7717/peerj.36/table-1</a></div>
+        </div>
+        <section class="sec">
+          <h3 class="heading">Extant animals</h3>
+          <p>Among extant animals, adult bull giraffes can attain a neck of 2.4 m (<cite itemprop="citation" itemscope="itemscope" itemref="ref-133" data-jats-ref-type="bibr" data-jats-rid="ref-133" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Okapis and giraffes&quot;" title="Okapis and giraffes" data-jats-ref-type="bibr" data-jats-rid="ref-133">Toon &amp; Toon, 2003</a></cite>, p. 399), and no other extant animal exceeds half of this. The typical length of the neck of the ostrich is only 1.0 m (sum of vertebral lengths in <cite itemprop="citation" itemscope="itemscope" itemref="ref-39" data-jats-ref-type="bibr" data-jats-rid="ref-39" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1002/jmor.10542" title="Flexibility along the neck of the ostrich (Struthio camelus) and consequences for the reconstruction of dinosaurs with extreme neck length" data-jats-ref-type="bibr" data-jats-rid="ref-39">Dzemski &amp; Christian (2007)</a></cite>, <a class="xref xref-table" href="#table-1" data-jats-ref-type="table" data-jats-rid="table-1">Table 1</a>, plus 8% to allow for intervertebral cartilage – see <cite itemprop="citation" itemscope="itemscope" itemref="ref-24" data-jats-ref-type="bibr" data-jats-rid="ref-24" itemtype=""><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;&quot;" title="" data-jats-ref-type="bibr" data-jats-rid="ref-24">Cobley, 2011</a></cite>, p. 16).</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Extinct mammals</h3>
+          <p>The largest terrestrial mammal of all time was the long-necked rhinoceratoid <i>Paraceratherium</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-41" data-jats-ref-type="bibr" data-jats-rid="ref-41" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Paraceratherium bugtiense, a new genus of Rhinocerotidae from the Bugti Hills of Baluchistan, preliminary notice&quot;" title="Paraceratherium bugtiense, a new genus of Rhinocerotidae from the Bugti Hills of Baluchistan, preliminary notice" data-jats-ref-type="bibr" data-jats-rid="ref-41">Forster-Cooper, 1911</a></cite> (= <i>Baluchitherium</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-42" data-jats-ref-type="bibr" data-jats-rid="ref-42" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Correction of generic name [Thaumastotherium to Baluchitherium]&quot;" title="Correction of generic name [Thaumastotherium to Baluchitherium]" data-jats-ref-type="bibr" data-jats-rid="ref-42">Forster-Cooper, 1913</a></cite>, <i>Indricotherium</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-12" data-jats-ref-type="bibr" data-jats-rid="ref-12" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Ob indrikoterii (Indricotherium n.g.)&quot;" title="Ob indrikoterii (Indricotherium n.g.)" data-jats-ref-type="bibr" data-jats-rid="ref-12">Borissiak, 1915</a></cite>). The length of its neck can be measured as 1.95 m from the skeletal reconstruction of <cite itemprop="citation" itemscope="itemscope" itemref="ref-53" data-jats-ref-type="bibr" data-jats-rid="ref-53" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Further notes on the gigantic extinct rhinoceros, Baluchitherium, from the Oligocene of Mongolia&quot;" title="Further notes on the gigantic extinct rhinoceros, Baluchitherium, from the Oligocene of Mongolia" data-jats-ref-type="bibr" data-jats-rid="ref-53">Granger &amp; Gregory (1936, figure 47)</a></cite>. This length, however, is rather shorter than suggested by the text (pp. 10–20), in which lengths of 39, 39, 36, 29.6 and 18 cm are given for cervicals 1, 2, 4, 6 and 7, even though C2 and C7 are reported as of “size class III”. When the lengths of C2 and C7 are multiplied by 1.3 to give lengths of equivalent “size class I” bones (<cite itemprop="citation" itemscope="itemscope" itemref="ref-53" data-jats-ref-type="bibr" data-jats-rid="ref-53" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Further notes on the gigantic extinct rhinoceros, Baluchitherium, from the Oligocene of Mongolia&quot;" title="Further notes on the gigantic extinct rhinoceros, Baluchitherium, from the Oligocene of Mongolia" data-jats-ref-type="bibr" data-jats-rid="ref-53">Granger &amp; Gregory, 1936, p. 65</a></cite>), their lengths become 50.7 and 23.4 cm. The total length of the preserved cervicals would then be 178.7 cm even though C3 and C5, which were not recovered, are omitted. If these vertebrae are tentatively assigned lengths intermediate between those that preceded and succeeded them (i.e., 43.4 and 32.8 cm) then the total length of all seven centra is 254.9 cm, more than 30% longer than the illustrated length. At any rate, the material available suggests a total neck length in the 2–2.5 m range.</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Theropods</h3>
+          <p>In each of the successively more derived clades Ornithodira, Dinosauria, and Saurischia, the primitive state was an increasingly long neck (<cite itemprop="citation" itemscope="itemscope" itemref="ref-49" data-jats-ref-type="bibr" data-jats-rid="ref-49" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Saurischian monophyly and the origin of birds&quot;" title="Saurischian monophyly and the origin of birds" data-jats-ref-type="bibr" data-jats-rid="ref-49">Gauthier, 1986</a></cite>; <cite itemprop="citation" itemscope="itemscope" itemref="ref-124" data-jats-ref-type="bibr" data-jats-rid="ref-124" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.2307/3889336" title="Basal archosaurs: phylogenetic relationships and functional implications" data-jats-ref-type="bibr" data-jats-rid="ref-124">Sereno, 1991a</a></cite>; <cite itemprop="citation" itemscope="itemscope" itemref="ref-71" data-jats-ref-type="bibr" data-jats-rid="ref-71" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Basal Saurischia&quot;" title="Basal Saurischia" data-jats-ref-type="bibr" data-jats-rid="ref-71">Langer, 2004</a></cite>). Within Saurischia, both branches of that clade, Sauropodomorpha and Theropoda, further elongated their necks (<cite itemprop="citation" itemscope="itemscope" itemref="ref-48" data-jats-ref-type="bibr" data-jats-rid="ref-48" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Prosauropoda&quot;" title="Prosauropoda" data-jats-ref-type="bibr" data-jats-rid="ref-48">Galton &amp; Upchurch, 2004</a></cite>). So sauropods inherited as their primitive state necks that were already more elongated, and heads that were proportionally smaller, than in most animals.</p>
+          <p>Within Theropoda, at least three lineages evolved especially long necks. The lengths of their necks can be estimated from their incomplete remains, though with some uncertainty, as follows.</p>
+          <p><i>Therizinosaurus cheloniformis</i><cite itemprop="citation" itemscope="itemscope" itemref="ref-78" data-jats-ref-type="bibr" data-jats-rid="ref-78" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;New turtle-like reptile in Mongolia&quot;" title="New turtle-like reptile in Mongolia" data-jats-ref-type="bibr" data-jats-rid="ref-78">Maleev, 1954</a></cite> is a bizarre, long-necked giant theropod, known from incomplete remains. Measuring from <cite itemprop="citation" itemscope="itemscope" itemref="ref-6" data-jats-ref-type="bibr" data-jats-rid="ref-6" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;New information on Therizinosaurus (Therizinosauridae, Theropoda)&quot;" title="New information on Therizinosaurus (Therizinosauridae, Theropoda)" data-jats-ref-type="bibr" data-jats-rid="ref-6">Barsbold (1976, figure 1)</a></cite>, its humerus was about 75 cm long. In a skeletal reconstruction of the therizinosauroid <i>Nanshiungosaurus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-38" data-jats-ref-type="bibr" data-jats-rid="ref-38" itemtype=""><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;&quot;" title="" data-jats-ref-type="bibr" data-jats-rid="ref-38">Dong, 1979</a></cite> by <cite itemprop="citation" itemscope="itemscope" itemref="ref-110" data-jats-ref-type="bibr" data-jats-rid="ref-110" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Dinosaur models: the good, the bad, and using them to estimate the mass of dinosaurs&quot;" title="Dinosaur models: the good, the bad, and using them to estimate the mass of dinosaurs" data-jats-ref-type="bibr" data-jats-rid="ref-110">Paul (1997, p. 145)</a></cite>, the neck is 2.9 times the length of the humerus. If <i>Therizinosaurus</i> were similarly proportioned, its neck would have been about 2.2 m long.</p>
+          <p>Another giant theropod, <i>Gigantoraptor erlianensis</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-156" data-jats-ref-type="bibr" data-jats-rid="ref-156" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;A gigantic bird-like dinosaur from the Late Cretaceous of China&quot;" title="A gigantic bird-like dinosaur from the Late Cretaceous of China" data-jats-ref-type="bibr" data-jats-rid="ref-156">Xu et al., 2007</a></cite> belongs to another long-necked group, Oviraptorosauria. Measured from the skeletal reconstruction of <cite itemprop="citation" itemscope="itemscope" itemref="ref-156" data-jats-ref-type="bibr" data-jats-rid="ref-156" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;A gigantic bird-like dinosaur from the Late Cretaceous of China&quot;" title="A gigantic bird-like dinosaur from the Late Cretaceous of China" data-jats-ref-type="bibr" data-jats-rid="ref-156">Xu et al. (2007, figure 1A)</a></cite>, it appears to have had a neck 2.15 m in length – although this is conjectural as almost no cervical material is known.</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Pterosaurs</h3>
+          <p>Although it is often noted in general terms that azhdarchid pterosaurs had long necks (e.g., <cite itemprop="citation" itemscope="itemscope" itemref="ref-56" data-jats-ref-type="bibr" data-jats-rid="ref-56" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1111/j.1096-3642.1986.tb02249.x" title="On the cervical vertebrae of the Pterodactyloidea (Reptilia: Archosauria)" data-jats-ref-type="bibr" data-jats-rid="ref-56">Howse, 1986</a></cite>; <cite itemprop="citation" itemscope="itemscope" itemref="ref-154" data-jats-ref-type="bibr" data-jats-rid="ref-154" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1371/journal.pone.000227" title="A reappraisal of azhdarchid pterosaur functional morphology and paleoecology" data-jats-ref-type="bibr" data-jats-rid="ref-154">Witton &amp; Naish, 2008</a></cite>), there are no published numeric estimates of neck length in this group. This is due to the lack of any published azhdarchid specimen with a complete neck (<cite itemprop="citation" itemscope="itemscope" itemref="ref-153" data-jats-ref-type="bibr" data-jats-rid="ref-153" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1371/journal.pone.0013982" title="On the size and flight diversity of giant pterosaurs, the use of birds as pterosaur analogues and comments on pterosaur flightlessness" data-jats-ref-type="bibr" data-jats-rid="ref-153">Witton &amp; Habib, 2010</a></cite>): <i>Quetzalcoatlus</i> specimens at the Texas Memorial Museum may have complete necks, but have been embargoed since the early 1980s (<cite itemprop="citation" itemscope="itemscope" itemref="ref-72" data-jats-ref-type="bibr" data-jats-rid="ref-72" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1038/scientificamerican0281-122" title="Pterosaurs" data-jats-ref-type="bibr" data-jats-rid="ref-72">Langston, 1981</a></cite>): a monographic description is still awaited. In the absence of a complete neck, all length estimates are uncertain, but it is nevertheless possible to arrive at an approximate length.</p>
+          <p>The azhdarchid for which the most complete neck has been described is <i>Zhejiangopterus linhaiensis</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-18" data-jats-ref-type="bibr" data-jats-rid="ref-18" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Zhejiangopterus linhaiensis (Pterosauria) from the Upper Cretaceous of Linhai, Zhejiang, China&quot;" title="Zhejiangopterus linhaiensis (Pterosauria) from the Upper Cretaceous of Linhai, Zhejiang, China" data-jats-ref-type="bibr" data-jats-rid="ref-18">Cai &amp; Wei, 1994</a></cite>, so we will base our estimates on this species. <cite itemprop="citation" itemscope="itemscope" itemref="ref-18" data-jats-ref-type="bibr" data-jats-rid="ref-18" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Zhejiangopterus linhaiensis (Pterosauria) from the Upper Cretaceous of Linhai, Zhejiang, China&quot;" title="Zhejiangopterus linhaiensis (Pterosauria) from the Upper Cretaceous of Linhai, Zhejiang, China" data-jats-ref-type="bibr" data-jats-rid="ref-18">Cai &amp; Wei (1994, table 7)</a></cite>, give the lengths of cervicals 3–7 for three specimens, ZMNH M1323, M1324 and M1328. In all three, C5 is the longest cervical, as is generally true of pterodacyloid pterosaurs including azhdarchids (<cite itemprop="citation" itemscope="itemscope" itemref="ref-56" data-jats-ref-type="bibr" data-jats-rid="ref-56" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1111/j.1096-3642.1986.tb02249.x" title="On the cervical vertebrae of the Pterodactyloidea (Reptilia: Archosauria)" data-jats-ref-type="bibr" data-jats-rid="ref-56">Howse, 1986, p. 323</a></cite>). <cite itemprop="citation" itemscope="itemscope" itemref="ref-18" data-jats-ref-type="bibr" data-jats-rid="ref-18" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Zhejiangopterus linhaiensis (Pterosauria) from the Upper Cretaceous of Linhai, Zhejiang, China&quot;" title="Zhejiangopterus linhaiensis (Pterosauria) from the Upper Cretaceous of Linhai, Zhejiang, China" data-jats-ref-type="bibr" data-jats-rid="ref-18">Cai &amp; Wei (1994)</a></cite> do not give lengths for C1 and C2, stating only that “the atlas-axis is completely fused and extremely short but morphological details are indistinct due to being obscured by the cranium” (p. 183, translation by Will Downs). Their figure 6, a reconstruction of <i>Zhejiangopterus linhaiensis</i>, bears this out, showing the atlas-axis as about one quarter the length of C3. Using this ratio to estimate the C1–2 lengths for each specimen, we find by adding the lengths of the individual cervicals that the three specimens had necks measuring approximately 511, 339 and 398 mm. These lengths are 3.60, 4.04 and 4.06 times the lengths of their respective C5s. On average, then, total C1–C7 neck length in known <i>Zhejiangopterus</i> specimens was about 3.85 times that of C5.</p>
+          <p>The azhdarchid <i>Arambourgiania philadelphiae</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-3" data-jats-ref-type="bibr" data-jats-rid="ref-3" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Titanopteryx philadelphiae nov. gen., nov. sp., ptérosaurien géant&quot;" title="Titanopteryx philadelphiae nov. gen., nov. sp., ptérosaurien géant" data-jats-ref-type="bibr" data-jats-rid="ref-3">Arambourg, 1959</a></cite> is the largest pterosaur for which cervical material has been described. Its type specimen, UJF VF1, is a single cervical vertebra. It was nearly complete when found, but has since been damaged and is now missing its central portion, but plaster replicas made before the damage indicate the extent of the missing portion. The preserved part of the vertebra was 620 mm long before the damage, and when complete it would have been about 780 mm long (<cite itemprop="citation" itemscope="itemscope" itemref="ref-84" data-jats-ref-type="bibr" data-jats-rid="ref-84" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Discovery of the holotype of the giant pterosaur Titanopteryx philadephiae (Arambourg, 1959) and the status of Arambourgiania and Quetzalcoatlus&quot;" title="Discovery of the holotype of the giant pterosaur Titanopteryx philadephiae (Arambourg, 1959) and the status of Arambourgiania and Quetzalcoatlus" data-jats-ref-type="bibr" data-jats-rid="ref-84">Martill et al., 1998, p. 72</a></cite>). Assuming that the preserved element is C5, as considered likely by <cite itemprop="citation" itemscope="itemscope" itemref="ref-56" data-jats-ref-type="bibr" data-jats-rid="ref-56" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1111/j.1096-3642.1986.tb02249.x" title="On the cervical vertebrae of the Pterodactyloidea (Reptilia: Archosauria)" data-jats-ref-type="bibr" data-jats-rid="ref-56">Howse (1986, p. 318)</a></cite> and <cite itemprop="citation" itemscope="itemscope" itemref="ref-43" data-jats-ref-type="bibr" data-jats-rid="ref-43" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;A reappraisal of Arambourgiania (Pterosauria, Pterodactyloidea): one of the world’s largest flying animals&quot;" title="A reappraisal of Arambourgiania (Pterosauria, Pterodactyloidea): one of the world’s largest flying animals" data-jats-ref-type="bibr" data-jats-rid="ref-43">Frey &amp; Martill (1996, p. 240)</a></cite>, the length of the C1–C7 region of the neck can be estimated as 3.85 times that length, which is 3.0 m.</p>
+          <figure class="fig" id="fig-3">
+            <div class="image-container">
+              <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-3-2x.jpg" title="View the full image" class="fresco" data-fresco-caption="Figure 3: Necks of long-necked sauropods, to scale." data-fresco-group="figure" data-fresco-options="fit: 'width', ui: 'outside', thumbnails: false, loop: true, position: true, preload: false">
+                <img class="graphic" src="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-3-1x.jpg" data-image-id="fig-3" alt="Necks of long-necked sauropods, to scale." data-full="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-3-full.png" data-thumb="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-3-thumb.jpg" data-original="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-3.png" data-image-type="figure" data-jats-mimetype="image" data-jats-mime-subtype="png"/>
+              </a>
+            </div>
+            <figcaption>
+              <h4 class="heading"><span class="caption-label">Figure 3: </span>Necks of long-necked sauropods, to scale.</h4>
+              <span class="p"><i>Diplodocus</i>, modified from elements in <cite itemprop="citation" itemscope="itemscope" itemref="ref-54" data-jats-ref-type="bibr" data-jats-rid="ref-54" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Diplodocus (Marsh): its osteology, taxonomy and probable habits, with a restoration of the skeleton&quot;" title="Diplodocus (Marsh): its osteology, taxonomy and probable habits, with a restoration of the skeleton" data-jats-ref-type="bibr" data-jats-rid="ref-54">Hatcher (1901, plate 3)</a></cite>, represents a “typical” long-necked sauropod, familiar from many mounted skeletons in museums. <i>Puertasaurus</i>, <i>Sauroposeidon</i>, <i>Mamenchisaurus</i> and <i>Supersaurus</i> modified from Scott Hartman’s reconstructions of <i>Futalognkosaurus</i>, <i>Cedarosaurus</i>, <i>Mamenchisaurus</i> and <i>Supersaurus</i> respectively. Alternating pink and blue bars are one meter in width. Inset shows <a class="xref xref-fig" href="#fig-1" data-jats-ref-type="fig" data-jats-rid="fig-1">Fig. 1</a> to the same scale.</span>
+              <div class="article-image-download">
+                <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-3-full.png" class="btn btn-mini" download="peerj-36-fig-3.png"><i class="icon-picture"> </i> Download full-size image</a>
+              </div>
+              <div class="object-id article-component-doi">DOI: <a href="http://dx.doi.org/10.7717/peerj.36/fig-3" rel="tooltip" title="Cite this object using this DOI">10.7717/peerj.36/fig-3</a></div>
+            </figcaption>
+          </figure>
+          <figure class="fig" id="fig-4">
+            <div class="image-container">
+              <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-4-2x.jpg" title="View the full image" class="fresco" data-fresco-caption="Figure 4: Extent of soft tissue on ostrich and sauropod necks." data-fresco-group="figure" data-fresco-options="fit: 'width', ui: 'outside', thumbnails: false, loop: true, position: true, preload: false">
+                <img class="graphic" src="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-4-1x.jpg" data-image-id="fig-4" alt="Extent of soft tissue on ostrich and sauropod necks." data-full="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-4-full.png" data-thumb="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-4-thumb.jpg" data-original="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-4.png" data-image-type="figure" data-jats-mimetype="image" data-jats-mime-subtype="png"/>
+              </a>
+            </div>
+            <figcaption>
+              <h4 class="heading"><span class="caption-label">Figure 4: </span>Extent of soft tissue on ostrich and sauropod necks.</h4>
+              <span class="p">1, Ostrich neck in cross section from <cite itemprop="citation" itemscope="itemscope" itemref="ref-139" data-jats-ref-type="bibr" data-jats-rid="ref-139" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1666/0094-8373(2003)029&lt;0243:VPASAT&gt;2.0.CO;2" title="Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs" data-jats-ref-type="bibr" data-jats-rid="ref-139">Wedel (2003, figure 2)</a></cite>. Bone is white, air-spaces are black, and soft tissue is grey. 2, Hypothetical sauropod neck with similarly proportioned soft-tissue. (<i>Diplodocus</i> vertebra silhouette modified from <cite itemprop="citation" itemscope="itemscope" itemref="ref-110" data-jats-ref-type="bibr" data-jats-rid="ref-110" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Dinosaur models: the good, the bad, and using them to estimate the mass of dinosaurs&quot;" title="Dinosaur models: the good, the bad, and using them to estimate the mass of dinosaurs" data-jats-ref-type="bibr" data-jats-rid="ref-110">Paul, 1997</a></cite>, figure 4A). The extent of soft tissue depicted greatly exceeds that shown in any published life restoration of a sauropod, and is unrealistic. 3, More realistic sauropod neck. It is not that the soft-tissue is reduced but that the vertebra within is enlarged, and mass is reduced by extensive pneumaticity in both the bone and the soft-tissue.</span>
+              <div class="article-image-download">
+                <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-4-full.png" class="btn btn-mini" download="peerj-36-fig-4.png"><i class="icon-picture"> </i> Download full-size image</a>
+              </div>
+              <div class="object-id article-component-doi">DOI: <a href="http://dx.doi.org/10.7717/peerj.36/fig-4" rel="tooltip" title="Cite this object using this DOI">10.7717/peerj.36/fig-4</a></div>
+            </figcaption>
+          </figure>
+          <figure class="fig" id="fig-5">
+            <div class="image-container">
+              <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-5-2x.jpg" title="View the full image" class="fresco" data-fresco-caption="Figure 5: Simplified myology of the sauropod neck, in left lateral view, based primarily on homology with birds, modified from Wedel &amp; Sanders (2002, figure 2)." data-fresco-group="figure" data-fresco-options="fit: 'width', ui: 'outside', thumbnails: false, loop: true, position: true, preload: false">
+                <img class="graphic" src="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-5-1x.jpg" data-image-id="fig-5" alt="Simplified myology of the sauropod neck, in left lateral view, based primarily on homology with birds, modified from Wedel &amp; Sanders (2002, figure 2)." data-full="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-5-full.png" data-thumb="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-5-thumb.jpg" data-original="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-5.png" data-image-type="figure" data-jats-mimetype="image" data-jats-mime-subtype="png"/>
+              </a>
+            </div>
+            <figcaption>
+              <h4 class="heading"><span class="caption-label">Figure 5: </span>Simplified myology of the sauropod neck, in left lateral view, based primarily on homology with birds, modified from <cite itemprop="citation" itemscope="itemscope" itemref="ref-146" data-jats-ref-type="bibr" data-jats-rid="ref-146" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Osteological correlates of cervical musculature in Aves and Sauropoda (Dinosauria: Saurischia), with comments on the cervical ribs of Apatosaurus&quot;" title="Osteological correlates of cervical musculature in Aves and Sauropoda (Dinosauria: Saurischia), with comments on the cervical ribs of Apatosaurus" data-jats-ref-type="bibr" data-jats-rid="ref-146">Wedel &amp; Sanders (2002, figure 2)</a></cite>.</h4>
+              <span class="p">Dashed arrows indicate muscle passing medially behind bone. A, B. Muscles inserting on the epipophyses, shown in red. C, D, E. Muscles inserting on the cervical ribs, shown in green. F, G. Muscles inserting on the neural spine, shown in blue. H. Muscles inserting on the ansa costotransversaria (“cervical rib loop”), shown in brown. Specifically: A. M. longus colli dorsalis. B. M. cervicalis ascendens. C. M. flexor colli lateralis. D. M. flexor colli medialis. E. M. longus colli ventralis. In birds, this muscle originates from the processes carotici, which are absent in the vertebrae of sauropods. F. Mm. intercristales. G. Mm. interspinales. H. Mm. intertransversarii. Vertebrae modified from <cite itemprop="citation" itemscope="itemscope" itemref="ref-50" data-jats-ref-type="bibr" data-jats-rid="ref-50" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Osteology of Apatosaurus, with special reference to specimens in the Carnegie Museum&quot;" title="Osteology of Apatosaurus, with special reference to specimens in the Carnegie Museum" data-jats-ref-type="bibr" data-jats-rid="ref-50">Gilmore (1936, plate 24)</a></cite>.</span>
+              <div class="article-image-download">
+                <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-5-full.png" class="btn btn-mini" download="peerj-36-fig-5.png"><i class="icon-picture"> </i> Download full-size image</a>
+              </div>
+              <div class="object-id article-component-doi">DOI: <a href="http://dx.doi.org/10.7717/peerj.36/fig-5" rel="tooltip" title="Cite this object using this DOI">10.7717/peerj.36/fig-5</a></div>
+            </figcaption>
+          </figure>
+          <figure class="fig" id="fig-6">
+            <div class="image-container">
+              <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-6-2x.jpg" title="View the full image" class="fresco" data-fresco-caption="Figure 6: Basic cervical vertebral architecture in archosaurs." data-fresco-group="figure" data-fresco-options="fit: 'width', ui: 'outside', thumbnails: false, loop: true, position: true, preload: false">
+                <img class="graphic" src="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-6-1x.jpg" data-image-id="fig-6" alt="Basic cervical vertebral architecture in archosaurs." data-full="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-6-full.png" data-thumb="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-6-thumb.jpg" data-original="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-6.png" data-image-type="figure" data-jats-mimetype="image" data-jats-mime-subtype="png"/>
+              </a>
+            </div>
+            <figcaption>
+              <h4 class="heading"><span class="caption-label">Figure 6: </span>Basic cervical vertebral architecture in archosaurs.</h4>
+              <span class="p">1, Seventh cervical vertebra of a turkey, <i>Meleagris gallopavo</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-76" data-jats-ref-type="bibr" data-jats-rid="ref-76" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Systema naturae per regnum tria naturae secundum classes, ordines, genera, species, cum characteribus, differentiis, synonimis, loci&quot;" title="Systema naturae per regnum tria naturae secundum classes, ordines, genera, species, cum characteribus, differentiis, synonimis, loci" data-jats-ref-type="bibr" data-jats-rid="ref-76">Linnaeus, 1758</a></cite>, traced from photographs by MPT. 2, Fifth cervical vertebra of the abelisaurid theropod <i>Majungasaurus crenatissimus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-37" data-jats-ref-type="bibr" data-jats-rid="ref-37" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Note sur les dinosauriens sauropodes &amp; théropodes du Cretace Superieur de Madagascar&quot;" title="Note sur les dinosauriens sauropodes &amp; théropodes du Cretace Superieur de Madagascar" data-jats-ref-type="bibr" data-jats-rid="ref-37">Depéret, 1896</a></cite>, UA 8678, traced from <cite itemprop="citation" itemscope="itemscope" itemref="ref-100" data-jats-ref-type="bibr" data-jats-rid="ref-100" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;The postcranial axial skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar&quot;" title="The postcranial axial skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar" data-jats-ref-type="bibr" data-jats-rid="ref-100">O’Connor (2007, figures 8 and 20)</a></cite>. In these taxa, the epipophyses and cervical ribs are aligned with the expected vectors of muscular forces. The epipophyses are both larger and taller than the neural spine, as expected based on their mechanical importance. The posterior surface of the neurapophysis is covered by a large rugosity, which is interpreted as an interspinous ligament scar like that of birds (<cite itemprop="citation" itemscope="itemscope" itemref="ref-100" data-jats-ref-type="bibr" data-jats-rid="ref-100" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;The postcranial axial skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar&quot;" title="The postcranial axial skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar" data-jats-ref-type="bibr" data-jats-rid="ref-100">O’Connor, 2007</a></cite>). Because this scar covers the entire posterior surface of the neurapophysis, it leaves little room for muscle attachments to the spine. 3, Fifth cervical vertebra of <i>Alligator mississippiensis</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-33" data-jats-ref-type="bibr" data-jats-rid="ref-33" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Histoire naturelle, generale et particuliere des reptiles, Volume 1&quot;" title="Histoire naturelle, generale et particuliere des reptiles, Volume 1" data-jats-ref-type="bibr" data-jats-rid="ref-33">Daudin, 1801</a></cite>, MCZ 81457, traced from 3D scans by Leon Claessens, courtesy of MCZ. Epipophyses are absent. 4, Eighth cervical vertebra of <i>Giraffatitan brancai</i> (<cite itemprop="citation" itemscope="itemscope" itemref="ref-61" data-jats-ref-type="bibr" data-jats-rid="ref-61" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Übersicht über der Wirbeltierfauna der Tendaguru-Schichten nebst einer kurzen Charakterisierung der neu aufgefuhrten Arten von Sauropoden&quot;" title="Übersicht über der Wirbeltierfauna der Tendaguru-Schichten nebst einer kurzen Charakterisierung der neu aufgefuhrten Arten von Sauropoden" data-jats-ref-type="bibr" data-jats-rid="ref-61">Janensch, 1914</a></cite>) paralectotype MB.R.2181, traced from <cite itemprop="citation" itemscope="itemscope" itemref="ref-64" data-jats-ref-type="bibr" data-jats-rid="ref-64" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Die Wirbelsaule von Brachiosaurus brancai&quot;" title="Die Wirbelsaule von Brachiosaurus brancai" data-jats-ref-type="bibr" data-jats-rid="ref-64">Janensch (1950, figures 43 and 46)</a></cite>. Abbreviations: cr, cervical rib; e, epipophysis; ns, neural spine; poz, postzygapophysis.</span>
+              <div class="article-image-download">
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+            </figcaption>
+          </figure>
+          <p>The total number of cervical vertebrae in <i>Zhejiangopterus</i> is not clear: <cite itemprop="citation" itemscope="itemscope" itemref="ref-18" data-jats-ref-type="bibr" data-jats-rid="ref-18" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Zhejiangopterus linhaiensis (Pterosauria) from the Upper Cretaceous of Linhai, Zhejiang, China&quot;" title="Zhejiangopterus linhaiensis (Pterosauria) from the Upper Cretaceous of Linhai, Zhejiang, China" data-jats-ref-type="bibr" data-jats-rid="ref-18">Cai &amp; Wei (1994)</a></cite> imply that there are seven, and their illustrations (<a class="xref xref-fig" href="#fig-5" data-jats-ref-type="fig" data-jats-rid="fig-5">Figs. 5</a> and <a class="xref xref-fig" href="#fig-6" data-jats-ref-type="fig" data-jats-rid="fig-6">6</a>) indicate that in at least one specimen the vertebral column is complete. However, at least some azhdarchids seem to have have nine cervical vertebrae (e.g., <i>Phosphatodraco</i>, <cite itemprop="citation" itemscope="itemscope" itemref="ref-111" data-jats-ref-type="bibr" data-jats-rid="ref-111" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://dx.doi.org/10.1144/GSL.SP.2003.217.01.08" title="A New Azhdarchid Pterosaur from the Late Cretaceous Phosphates of Morocco" data-jats-ref-type="bibr" data-jats-rid="ref-111">Pereda-Suberbiola et al., 2003</a></cite>), although the ninth “cervical” bears a long vertically oriented rib and must have contributed to the length of the torso rather than the neck. Bearing this in mind, the total neck length of <i>Arambourgiania</i> may have somewhat exceeded 3.0 m. In azhdarchids, C8 may be between 20% and 50% the length of C5 (<cite itemprop="citation" itemscope="itemscope" itemref="ref-111" data-jats-ref-type="bibr" data-jats-rid="ref-111" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://dx.doi.org/10.1144/GSL.SP.2003.217.01.08" title="A New Azhdarchid Pterosaur from the Late Cretaceous Phosphates of Morocco" data-jats-ref-type="bibr" data-jats-rid="ref-111">Pereda-Suberbiola et al., 2003, p. 86</a></cite>), which might amount to 16–39 cm in <i>Arambourgiania.</i></p>
+          <p>Another azhdarchid, <i>Hatzegopteryx thambema</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-16" data-jats-ref-type="bibr" data-jats-rid="ref-16" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1007/s00114-002-0307-1" title="A new giant pterosaur with a robust skull from the latest Cretaceous of Romania" data-jats-ref-type="bibr" data-jats-rid="ref-16">Buffetaut, Grigorescu &amp; Csiki (2002)</a></cite>, may have been even larger than <i>Arambourgiania</i>, but no cervical material is known. Since its skull was much more robust that those of other azhdarchids (<cite itemprop="citation" itemscope="itemscope" itemref="ref-16" data-jats-ref-type="bibr" data-jats-rid="ref-16" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1007/s00114-002-0307-1" title="A new giant pterosaur with a robust skull from the latest Cretaceous of Romania" data-jats-ref-type="bibr" data-jats-rid="ref-16">Buffetaut, Grigorescu &amp; Csiki, 2002, p. 183</a></cite>), it was probably carried on a proportionally shorter and stronger neck.</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Plesiosaurs</h3>
+          <p>As marine reptiles, plesiosaurs benefited from the support of water and so lived under a wholly different biomechanical regime than terrestrial animals. The long necks of elasmosaurid plesiosaurs were constructed very differently from those of sauropods, consisting of many very short cervicals – 76 in the neck of <i>Albertonectes vanderveldei</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-69" data-jats-ref-type="bibr" data-jats-rid="ref-69" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1080/02724634.2012.658124" title="Albertonectes vanderveldei, a new elasmosaur (Reptilia, Sauropterygia) from the Upper Cretaceous of Alberta" data-jats-ref-type="bibr" data-jats-rid="ref-69">Kubo, Mitchell &amp; Henderson, 2012</a></cite> and 71 in <i>Elasmosaurus platyurus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-25" data-jats-ref-type="bibr" data-jats-rid="ref-25" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Remarks on a new enaliosaurian, Elasmosaurus platyurus&quot;" title="Remarks on a new enaliosaurian, Elasmosaurus platyurus" data-jats-ref-type="bibr" data-jats-rid="ref-25">Cope, 1868</a></cite> (<cite itemprop="citation" itemscope="itemscope" itemref="ref-116" data-jats-ref-type="bibr" data-jats-rid="ref-116" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Redescription of Elasmosaurus platyurus Cope, 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (Lower Campanian) of Kansas, U.S.A&quot;" title="Redescription of Elasmosaurus platyurus Cope, 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (Lower Campanian) of Kansas, U.S.A" data-jats-ref-type="bibr" data-jats-rid="ref-116">Sachs, 2005, p. 92</a></cite>). Despite their marine lifestyle and very numerous cervicals, elasmosaurids did not attain neck lengths even half those of the longest-necked sauropods. According to <cite itemprop="citation" itemscope="itemscope" itemref="ref-69" data-jats-ref-type="bibr" data-jats-rid="ref-69" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1080/02724634.2012.658124" title="Albertonectes vanderveldei, a new elasmosaur (Reptilia, Sauropterygia) from the Upper Cretaceous of Alberta" data-jats-ref-type="bibr" data-jats-rid="ref-69">Kubo, Mitchell &amp; Henderson (2012, p. 570)</a></cite>, “The approximately 7 m long neck of <i>Albertonectes</i> is the longest known for elasmosaurs (equal to 62% of total postcranial length).” Since the neck of <i>Albertonectes</i> was found articulated, the reported total neck length presumably includes the invertebral cartilage. Other elasmosaurs may have had equally long necks. The cervical vertebrae of <i>Elasmosaurus platyurus</i> holotype ANSP 10081 sum to 610.5 cm, based on individual vertebral lengths listed by <cite itemprop="citation" itemscope="itemscope" itemref="ref-116" data-jats-ref-type="bibr" data-jats-rid="ref-116" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Redescription of Elasmosaurus platyurus Cope, 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (Lower Campanian) of Kansas, U.S.A&quot;" title="Redescription of Elasmosaurus platyurus Cope, 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (Lower Campanian) of Kansas, U.S.A" data-jats-ref-type="bibr" data-jats-rid="ref-116">Sachs (2005, p. 95)</a></cite>. For other plesiosaurs, <cite itemprop="citation" itemscope="itemscope" itemref="ref-40" data-jats-ref-type="bibr" data-jats-rid="ref-40" itemtype=""><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;&quot;" title="" data-jats-ref-type="bibr" data-jats-rid="ref-40">Evans (1993)</a></cite> estimated that the thickness of intercervical cartilage amounted to 14% of centrum length in <i>Muraenosaurus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-120" data-jats-ref-type="bibr" data-jats-rid="ref-120" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1144/GSL.JGS.1874.030.01-04.35" title="On Muraenosaurus leedsii, a plesosaurian from the Oxford Clay" data-jats-ref-type="bibr" data-jats-rid="ref-120">Seeley, 1874</a></cite> and 20% in <i>Cryptoclidus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-121" data-jats-ref-type="bibr" data-jats-rid="ref-121" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1098/rspl.1892.0017" title="The nature of the shoulder girdle and clavicular arch in the Sauropterygia" data-jats-ref-type="bibr" data-jats-rid="ref-121">Seeley, 1892</a></cite>. Using the average of 17% for <i>Elasmosaurus</i>, we can estimate its total neck length as 7.1 m (<a class="xref xref-fig" href="#fig-2" data-jats-ref-type="fig" data-jats-rid="fig-2">Fig. 2.4</a>). This is within 6% of <cite itemprop="citation" itemscope="itemscope" itemref="ref-75" data-jats-ref-type="bibr" data-jats-rid="ref-75" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;On the Elasmosaurus platyurus of Cope&quot;" title="On the Elasmosaurus platyurus of Cope" data-jats-ref-type="bibr" data-jats-rid="ref-75">Leidy</a></cite>’s (<cite itemprop="citation" itemscope="itemscope" itemref="ref-75" data-jats-ref-type="bibr" data-jats-rid="ref-75" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;On the Elasmosaurus platyurus of Cope&quot;" title="On the Elasmosaurus platyurus of Cope" data-jats-ref-type="bibr" data-jats-rid="ref-75">1870</a></cite>) estimate of “almost twenty-two feet”, or about 6.7 m, and approximately equal to the 7-m neck length reported for <i>Albertonectes</i> by <cite itemprop="citation" itemscope="itemscope" itemref="ref-69" data-jats-ref-type="bibr" data-jats-rid="ref-69" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1080/02724634.2012.658124" title="Albertonectes vanderveldei, a new elasmosaur (Reptilia, Sauropterygia) from the Upper Cretaceous of Alberta" data-jats-ref-type="bibr" data-jats-rid="ref-69">Kubo, Mitchell &amp; Henderson (2012)</a></cite>.</p>
+          <p>These longest necks are in the <i>Diplodocus</i> class. They lack most of the characters that we later identify as contributing to neck length in sauropods, but solved the support issue by being marine. We know from whales (see below) that a 7 m trachea need not impose the difficulties we might expect; but we don’t know whether sufficiently large lungs would fit inside an elasmosaur torso. So far, little work has been done on the physiological implications of neck elongation in plesiosaurs; more is needed.</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Tanystropheus</h3>
+          <p>The bizarre prolacertiform <i>Tanystropheus</i> merits mention as possessing perhaps the longest neck relative to torso length of any animal. The complete skeleton PIMUZ T 2818 has a total length of 420 cm (<cite itemprop="citation" itemscope="itemscope" itemref="ref-98" data-jats-ref-type="bibr" data-jats-rid="ref-98" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Tanystropheus longobardicus (Reptilia, Protorosauria): reinterpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy)&quot;" title="Tanystropheus longobardicus (Reptilia, Protorosauria): reinterpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy)" data-jats-ref-type="bibr" data-jats-rid="ref-98">Nosotti, 2007, p. 8</a></cite>), of which the neck accounts for 211.2 cm (<cite itemprop="citation" itemscope="itemscope" itemref="ref-134" data-jats-ref-type="bibr" data-jats-rid="ref-134" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Allometry and heterochrony in the growth of the neck of Triassic prolacertiform reptiles&quot;" title="Allometry and heterochrony in the growth of the neck of Triassic prolacertiform reptiles" data-jats-ref-type="bibr" data-jats-rid="ref-134">Tschanz, 1988, p. 1003</a></cite>) – almost exactly half. <cite itemprop="citation" itemscope="itemscope" itemref="ref-98" data-jats-ref-type="bibr" data-jats-rid="ref-98" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Tanystropheus longobardicus (Reptilia, Protorosauria): reinterpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy)&quot;" title="Tanystropheus longobardicus (Reptilia, Protorosauria): reinterpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy)" data-jats-ref-type="bibr" data-jats-rid="ref-98">Nosotti (2007, p. 8)</a></cite> estimates the total length of the incomplete specimen PIMUZ T 2793 as 535 cm. If it were similarly proportioned to PIMUZ T 2818, its neck would have measured 269 cm.</p>
+          <p>Despite more than a century of study, there is no consensus on the habits or even environment of <i>Tanystropheus</i>. However, <cite itemprop="citation" itemscope="itemscope" itemref="ref-98" data-jats-ref-type="bibr" data-jats-rid="ref-98" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Tanystropheus longobardicus (Reptilia, Protorosauria): reinterpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy)&quot;" title="Tanystropheus longobardicus (Reptilia, Protorosauria): reinterpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy)" data-jats-ref-type="bibr" data-jats-rid="ref-98">Nosotti (2007, p. 76)</a></cite> argues that limb proportions “unequivocally indicate the adaptation to an aquatic mode of life”. If this is correct, then its neck was subject to a quite different biomechanical regime than those of sauropods.</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Sauropods</h3>
+          <p>The necks of sauropod dinosaurs greatly exceeded in length those of all other animals (<cite itemprop="citation" itemscope="itemscope" itemref="ref-141" data-jats-ref-type="bibr" data-jats-rid="ref-141" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Pneumaticity, neck length, and body size in sauropods&quot;" title="Pneumaticity, neck length, and body size in sauropods" data-jats-ref-type="bibr" data-jats-rid="ref-141">Wedel, 2006a</a></cite>). As noted above, they inherited long necks from their basal sauropodomorph ancestors. From this base, they elongated them yet further – both in ancestral forms and further still in more derived groups. Exceptionally long necks evolved in at least four distinct sauropod lineages (<a class="xref xref-fig" href="#fig-3" data-jats-ref-type="fig" data-jats-rid="fig-3">Fig. 3</a>).</p>
+          <p>The basal eusauropod <i>Mamenchisaurus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-158" data-jats-ref-type="bibr" data-jats-rid="ref-158" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;On a new sauropod from Yiping, Szechuan, China&quot;" title="On a new sauropod from Yiping, Szechuan, China" data-jats-ref-type="bibr" data-jats-rid="ref-158">Young, 1954</a></cite> is known from several species. One, <i>M. hochuanensis</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-159" data-jats-ref-type="bibr" data-jats-rid="ref-159" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Mamenchisaurus hochuanensis sp. nov&quot;" title="Mamenchisaurus hochuanensis sp. nov" data-jats-ref-type="bibr" data-jats-rid="ref-159">Young &amp; Zhao, 1972</a></cite>, is known from an individual with a complete neck that is 9.5 m in length (personal measurement, MPT). Another species, <i>M. sinocanadorum</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-115" data-jats-ref-type="bibr" data-jats-rid="ref-115" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1139/e93-180" title="A large mamenchisaurid from the Junggar Basin, Xinjiang, People’s Republic of China" data-jats-ref-type="bibr" data-jats-rid="ref-115">Russell &amp; Zheng, 1993</a></cite> is known only from skull elements and anterior cervical vertebrae, but by comparing this material with the corresponding elements of <i>M. hochuanensis</i>, its neck can be estimated to have been about 12 m long.</p>
+          <p>The known material of the diplodocid <i>Supersaurus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-65" data-jats-ref-type="bibr" data-jats-rid="ref-65" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Three new sauropod dinosaurs from the Upper Jurassic of Colorado&quot;" title="Three new sauropod dinosaurs from the Upper Jurassic of Colorado" data-jats-ref-type="bibr" data-jats-rid="ref-65">Jensen, 1985</a></cite> includes a cervical vertebra whose centrum is 138 cm long. Comparing this with the lengths of similar vertebrae from the closely related <i>Barosaurus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-83" data-jats-ref-type="bibr" data-jats-rid="ref-83" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Description of new dinosaurian reptiles&quot;" title="Description of new dinosaurian reptiles" data-jats-ref-type="bibr" data-jats-rid="ref-83">Marsh, 1890</a></cite>, for which much more complete necks are known, suggests a complete neck length in the region of 15 m (<cite itemprop="citation" itemscope="itemscope" itemref="ref-143" data-jats-ref-type="bibr" data-jats-rid="ref-143" itemtype=""><a class="xref xref-bibr" href="http://sauroposeidon.files.wordpress.com/2010/04/wedel-2007-dissertation.pdf" title="" data-jats-ref-type="bibr" data-jats-rid="ref-143">Wedel, 2007a, p. 197</a></cite>).</p>
+          <p>The holotype and largest known specimen of <i>Sauroposeidon</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-147" data-jats-ref-type="bibr" data-jats-rid="ref-147" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1671/0272-4634(2000)020[0109:SPANSF]2.0.CO;2" title="Sauroposeidon proteles, a new sauropod from the early cretaceous of Oklahoma" data-jats-ref-type="bibr" data-jats-rid="ref-147">Wedel, Cifelli &amp; Sanders, 2000a</a></cite> consists of a sequence of four articulated cervical vertebrae, the largest of which has a centrum 125 cm long. The complete cervical series of the morphologically similar and possibly closely related brachiosaurid <i>Giraffatitan</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-109" data-jats-ref-type="bibr" data-jats-rid="ref-109" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus&quot;" title="The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus" data-jats-ref-type="bibr" data-jats-rid="ref-109">Paul, 1988</a></cite> is known, and consists of 13 cervicals measuring 8.5 m. The <i>Sauroposeidon</i> cervicals are on average 37% longer than the corresponding vertebrae of <i>Giraffatitan</i>, suggesting a complete neck length of about 11.5 m. If <i>Sauroposeidon</i> is a basal somphospondyl rather than a brachiosaurid, as suggested by <cite itemprop="citation" itemscope="itemscope" itemref="ref-36" data-jats-ref-type="bibr" data-jats-rid="ref-36" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1080/02724634.2012.671204" title="The beginning of the sauropod dinosaur hiatus in North America: insights from the Lower Cretaceous Cloverly Formation of Wyoming" data-jats-ref-type="bibr" data-jats-rid="ref-36">D’Emic &amp; Foreman (2012)</a></cite>, then a more apposite comparison might be to <i>Euhelopus</i>, which had 17 cervicals. The complete cervical series of <i>Euhelopus</i> PMU R233 is 13.2 times the length of the longest cervical (3765 mm vs 285 mm; <cite itemprop="citation" itemscope="itemscope" itemref="ref-151" data-jats-ref-type="bibr" data-jats-rid="ref-151" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Die Kreide-Dinosaurier aus Shantung&quot;" title="Die Kreide-Dinosaurier aus Shantung" data-jats-ref-type="bibr" data-jats-rid="ref-151">Wiman, 1929</a></cite>). Applying a similar scaling relationship to <i>Sauroposeidon</i>, and conservatively assuming that the largest available vertebra was the longest in the neck, yields an estimated neck length of 16.5 m. We will not know which of the two estimates is more accurate until more articulated cervical material of <i>Sauroposeidon</i> comes to light.</p>
+          <p><i>Puertasaurus</i><cite itemprop="citation" itemscope="itemscope" itemref="ref-99" data-jats-ref-type="bibr" data-jats-rid="ref-99" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Giant titanosaur (Dinosauria, Sauropoda) from the Late Cretaceous of Patagonia&quot;" title="Giant titanosaur (Dinosauria, Sauropoda) from the Late Cretaceous of Patagonia" data-jats-ref-type="bibr" data-jats-rid="ref-99">Novas et al., 2005</a></cite> is the largest titanosaur for which cervical material has been described. The single known cervical vertebra is 118 cm in total length, including overhanging prezygapophyses, and its incomplete centrum can be reconstructed after related titanosaurs as having been 105 cm long. Cross-scaling with <i>Malawisaurus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-59" data-jats-ref-type="bibr" data-jats-rid="ref-59" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;New material of an Early Cretaceous titanosaurid sauropod dinosaur from Malawi&quot;" title="New material of an Early Cretaceous titanosaurid sauropod dinosaur from Malawi" data-jats-ref-type="bibr" data-jats-rid="ref-59">Jacobs et al., 1993</a></cite>, which has the most similar cervical vertebrae among titanosaurs known from complete cervical material, yields a total neck length of 9 m.</p>
+          <p><a class="xref xref-table" href="#table-1" data-jats-ref-type="table" data-jats-rid="table-1">Table 1</a> lists a selection of sauropods, mostly known from complete or nearly complete necks, showing how they vary in length, cervical count, centrum length, cervical rib length, and maximum elongation index.</p>
+        </section>
+      </section>
+      <section class="sec">
+        <h2 class="heading">Factors Enabling Long Necks</h2>
+        <p>Discounting the aquatic plesiosaurs, whose necks were subject to different forces from those of terrestrial animals, neck-length limits in the range of two to three meters seem to apply to every group except sauropods, which exceeded this limit by a factor of five. Whatever mechanical barriers prevented the evolution of truly long necks in other terrestrial vertebrates, sauropods did not just break that barrier – they smashed it. Since four separate sauropod lineages evolved necks three or four times longer than those of any of their rivals, it seems likely that sauropods shared a suite of features that facilitated the evolution of such long necks. What were these features?</p>
+        <section class="sec">
+          <h3 class="heading">Absolutely large body size</h3>
+          <p>It is obviously impossible for a terrestrial animal with a torso the size of a giraffe’s to carry a 10 m neck. Sheer size is probably a necessary, but not sufficient, condition for evolving an absolutely long neck. Mere isometric scaling would of course suffice for larger animals to have longer necks, but <cite itemprop="citation" itemscope="itemscope" itemref="ref-108" data-jats-ref-type="bibr" data-jats-rid="ref-108" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;The origins of high browsing and the effects of phylogeny and scaling on neck length in sauropodomorphs&quot;" title="The origins of high browsing and the effects of phylogeny and scaling on neck length in sauropodomorphs" data-jats-ref-type="bibr" data-jats-rid="ref-108">Parrish (2006, p. 213)</a></cite> found a stronger result: that neck length is positively allometric with respect to body size in sauropods, varying with torso length to the power 1.35. This suggests that the necks of super-giant sauropods may have been even longer than imagined: <cite itemprop="citation" itemscope="itemscope" itemref="ref-20" data-jats-ref-type="bibr" data-jats-rid="ref-20" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus (Cope, 1878)&quot;" title="Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus (Cope, 1878)" data-jats-ref-type="bibr" data-jats-rid="ref-20">Carpenter (2006, p. 133)</a></cite> estimated the neck length of the apocryphal giant <i>Amphicoelias fragillimus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-28" data-jats-ref-type="bibr" data-jats-rid="ref-28" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1086/272176" title="Geology and paleontology: a new species of Amphicoelias" data-jats-ref-type="bibr" data-jats-rid="ref-28">Cope, 1878</a></cite> as 16.75 m, 2.21 times the length of 7.5 m used for <i>Diplodocus</i>, but if Parrish’s allometric curve pertained then the true value would have been 2.21<sup>1.35</sup> = 2.92 times as long as the neck of <i>Diplodocus</i>, or 21.9 m; and the longest single vertebra would have been 187 cm long.</p>
+          <p>The allometric equation of <cite itemprop="citation" itemscope="itemscope" itemref="ref-108" data-jats-ref-type="bibr" data-jats-rid="ref-108" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;The origins of high browsing and the effects of phylogeny and scaling on neck length in sauropodomorphs&quot;" title="The origins of high browsing and the effects of phylogeny and scaling on neck length in sauropodomorphs" data-jats-ref-type="bibr" data-jats-rid="ref-108">Parrish (2006)</a></cite> is descriptive, but does not in itself suggest a causal link between size and neck length. As noted by <cite itemprop="citation" itemscope="itemscope" itemref="ref-148" data-jats-ref-type="bibr" data-jats-rid="ref-148" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon&quot;" title="Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon" data-jats-ref-type="bibr" data-jats-rid="ref-148">Wedel, Cifelli &amp; Sanders (2000b, p. 377)</a></cite>, one possible explanation is that, because of their size, sauropods were under strong selection for larger feeding envelopes, which drove them to evolve longer necks.</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Quadrupedal stance</h3>
+          <p>One of the key innovations in the evolution of sauropods was quadrupedality, facilitated by characters such as forelimb elongation, columnar limbs and short metapodials (<cite itemprop="citation" itemscope="itemscope" itemref="ref-149" data-jats-ref-type="bibr" data-jats-rid="ref-149" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.2307/3889325" title="Early evolution and higher-level phylogeny of sauropod dinosaurs" data-jats-ref-type="bibr" data-jats-rid="ref-149">Wilson &amp; Sereno, 1998</a></cite>, p. 24). As well as providing a platform for the evolution of large body size, the stability of the quadrupedal posture also enabled the evolution of longer necks: although progressive elongation displaced the centre of mass forwards from above the hindlimbs, it remained in the stable region between fore and hindlimbs.</p>
+          <p>Computer modelling shows that theropod dinosaurs such as <i>Tyrannosaurus rex</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-102" data-jats-ref-type="bibr" data-jats-rid="ref-102" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Tyrannosaurus and other Cretaceous carnivorous dinosaurs&quot;" title="Tyrannosaurus and other Cretaceous carnivorous dinosaurs" data-jats-ref-type="bibr" data-jats-rid="ref-102">Osborn, 1905</a></cite> attained masses of 7 or even 10 tonnes (<cite itemprop="citation" itemscope="itemscope" itemref="ref-58" data-jats-ref-type="bibr" data-jats-rid="ref-58" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1371/journal.pone.0026037" title="A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth" data-jats-ref-type="bibr" data-jats-rid="ref-58">Hutchinson et al., 2011</a></cite>), and other giant theropods including <i>Therizinosaurus</i> and <i>Gigantoraptor</i> were probably of comparable size. However, they did not evolve necks as long as those of sauropods with similar mass, probably in part for this reason: the increased moment caused by neck elongation in a biped must be counteracted by an equal moment caused by a longer or more massive tail, increasing the physiological cost.</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Small head</h3>
+          <p>Sauropods inherited proportionally small heads from ancestral sauropodomorphs, and continued to reduce their proportional size. In many clades, they were further lightened by reduced dentition, because unlike other large-bodied animals such as hadrosaurs, ceratopsians and elephants, sauropods did not orally process their food. Sauropod heads were simple cropping devices with a brain and sense organs, and did not require special equipment for obtaining food, such as the long beaks of azhdarchids (<cite itemprop="citation" itemscope="itemscope" itemref="ref-21" data-jats-ref-type="bibr" data-jats-rid="ref-21" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1007/s00114-010-0650-6" title="First complete sauropod dinosaur skull from the Cretaceous of the Americas and the evolution of sauropod dentition" data-jats-ref-type="bibr" data-jats-rid="ref-21">Chure et al., 2010</a></cite>, pp. 388–389). The reduction in head weight would have reduced the required lifting power of the necks that carried them, and therefore the muscle and ligament mass could be reduced, allowing the necks to be longer than would have been possible with heavier heads. Other groups of large-bodied animals have not evolved long necks, instead either developing large heads on short necks (ceratopsians, proboscideans, tyrannosaurs) or a compromise of a medium-sized head on a medium-length neck (hadrosaurs, indricotheres). It is significant that all other clades of large (&gt;10 ton) terrestrial herbivores – ceratopsians, hadrosaurs, proboscideans, and indricotheres – practiced extensive oral processing of their food, requiring massive dentition and correspondingly large heads.</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Numerous cervical vertebrae</h3>
+          <p>Many groups of animals seem to be constrained as to the number of cervical vertebrae they can evolve. With the exceptions of sloths and sirenians, mammals are all limited to exactly seven cervicals due to developmental constraints: mutations to the Hox genes that control the number of cervicals also give rise to neonatal cancer and other birth defects (<cite itemprop="citation" itemscope="itemscope" itemref="ref-45" data-jats-ref-type="bibr" data-jats-rid="ref-45" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1002/(SICI)1097-010X(19990415)285:1&lt;19::AID-JEZ3&gt;3.0.CO;2-Z" title="Why do almost all mammals have seven cervical vertebrae? Developmental constraints, Hox genes, and cancer" data-jats-ref-type="bibr" data-jats-rid="ref-45">Galis, 1999</a></cite>; <cite itemprop="citation" itemscope="itemscope" itemref="ref-46" data-jats-ref-type="bibr" data-jats-rid="ref-46" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1002/bies.10366" title="Anti-cancer selection as a source of developmental and evolutionary constraints" data-jats-ref-type="bibr" data-jats-rid="ref-46">Galis &amp; Metz, 2003</a></cite>). Azdarchids are variously reported as having seven to nine cervical vertebrae, but never more; non-avian theropods do not seem to have exceeded the 13 or perhaps 14 cervicals of <i>Neimongosaurus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-160" data-jats-ref-type="bibr" data-jats-rid="ref-160" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;A long-necked therizinosauroid dinosaur from the Upper Cretaceous Iren Dabasu Formation of Nei Mongol, People’s Republic of China&quot;" title="A long-necked therizinosauroid dinosaur from the Upper Cretaceous Iren Dabasu Formation of Nei Mongol, People’s Republic of China" data-jats-ref-type="bibr" data-jats-rid="ref-160">Zhang et al., 2001</a></cite>, with eleven or fewer being more typical.</p>
+          <p>By contrast, sauropods repeatedly increased the number of their cervical vertebrae, attaining as many as 19 in <i>Mamenchisaurus hochuanensis</i> (<cite itemprop="citation" itemscope="itemscope" itemref="ref-159" data-jats-ref-type="bibr" data-jats-rid="ref-159" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Mamenchisaurus hochuanensis sp. nov&quot;" title="Mamenchisaurus hochuanensis sp. nov" data-jats-ref-type="bibr" data-jats-rid="ref-159">Young &amp; Zhao, 1972</a></cite>, p. 3–7). Modern swans have up to 25 cervical vertebrae, and as noted above the marine reptile <i>Albertonectes</i> had 76 cervical vertebrae. Multiplication of cervical vertebrae obviously contributes to neck elongation.</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Elongate cervical vertebrae</h3>
+          <p>The shape of cervical vertebrae is quantified by the elongation index (EI), defined by <cite itemprop="citation" itemscope="itemscope" itemref="ref-148" data-jats-ref-type="bibr" data-jats-rid="ref-148" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon&quot;" title="Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon" data-jats-ref-type="bibr" data-jats-rid="ref-148">Wedel, Cifelli &amp; Sanders (2000b, p. 346)</a></cite> as the anteroposterior length of the centrum divided by the midline height of its posterior articular face. As shown in <a class="xref xref-table" href="#table-1" data-jats-ref-type="table" data-jats-rid="table-1">Table 1</a>, EI in sauropods routinely exceeded 4.0, and in some cases exceeded 6.0: <i>Sauroposeidon</i> C6 attained 6.1, and <i>Erketu</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-68" data-jats-ref-type="bibr" data-jats-rid="ref-68" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1206/0003-0082(2006)3508[1:EEALSF]2.0.CO;2" title="Erketu ellisoni, a long-necked sauropod from Bor Guve (Dornogov Aimag, Mongolia)" data-jats-ref-type="bibr" data-jats-rid="ref-68">Ksepka &amp; Norell, 2006</a></cite> C5 attained 7.0.</p>
+          <p>A similar degree of elongation is approached by the ostrich, in which C12 can attain an EI of 4.4 (measured from <cite itemprop="citation" itemscope="itemscope" itemref="ref-93" data-jats-ref-type="bibr" data-jats-rid="ref-93" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1111/j.1096-3642.1874.tb00564.x" title="On the axial skeleton of the ostrich (Struthio camelus)" data-jats-ref-type="bibr" data-jats-rid="ref-93">Mivart, 1874</a></cite>, figure 29), and by the giraffe, in which the axis can attain an EI of 4.71 (personal measurement of FMNH 34426). It is greatly exceeded by azhdarchid pterosaurs, among which C5 of <i>Quetzalcoatlus</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-74" data-jats-ref-type="bibr" data-jats-rid="ref-74" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1126/science.188.4189.676-a" title="Could pterosaurs fly?" data-jats-ref-type="bibr" data-jats-rid="ref-74">Lawson, 1975</a></cite> can attain an astonishing 12.4 (measured from <cite itemprop="citation" itemscope="itemscope" itemref="ref-154" data-jats-ref-type="bibr" data-jats-rid="ref-154" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1371/journal.pone.000227" title="A reappraisal of azhdarchid pterosaur functional morphology and paleoecology" data-jats-ref-type="bibr" data-jats-rid="ref-154">Witton &amp; Naish (2008, figure 4c)</a></cite>) and an isolated cervical from the Hell Creek Formation might have achieved 15 (measured from <cite itemprop="citation" itemscope="itemscope" itemref="ref-55" data-jats-ref-type="bibr" data-jats-rid="ref-55" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1671/0272-4634(2006)26[192:AAPCVF]2.0.CO;2" title="An azhdarchid pterosaur cervical vertebra from the Hell Creek Formation (Maastrichtian) of southeastern Montana" data-jats-ref-type="bibr" data-jats-rid="ref-55">Henderson &amp; Peterson (2006, figure 3)</a></cite>).</p>
+          <p>But other long-necked groups are more limited in their elongation of individual vertebrae. <i>Paraceratherium</i> seems have been limited to about 3.3 for C2 (measured from <cite itemprop="citation" itemscope="itemscope" itemref="ref-53" data-jats-ref-type="bibr" data-jats-rid="ref-53" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Further notes on the gigantic extinct rhinoceros, Baluchitherium, from the Oligocene of Mongolia&quot;" title="Further notes on the gigantic extinct rhinoceros, Baluchitherium, from the Oligocene of Mongolia" data-jats-ref-type="bibr" data-jats-rid="ref-53">Granger &amp; Gregory</a></cite> (<cite itemprop="citation" itemscope="itemscope" itemref="ref-53" data-jats-ref-type="bibr" data-jats-rid="ref-53" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Further notes on the gigantic extinct rhinoceros, Baluchitherium, from the Oligocene of Mongolia&quot;" title="Further notes on the gigantic extinct rhinoceros, Baluchitherium, from the Oligocene of Mongolia" data-jats-ref-type="bibr" data-jats-rid="ref-53">1936</a></cite>, figure 7)) and much less for the other vertebrae. Elongation indexes of therizinosaurs such as <i>Therizinosaurus</i> probably did not greatly exceed 1.0 (measured for <i>Nanshiungosaurus</i> from <cite itemprop="citation" itemscope="itemscope" itemref="ref-38" data-jats-ref-type="bibr" data-jats-rid="ref-38" itemtype=""><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;&quot;" title="" data-jats-ref-type="bibr" data-jats-rid="ref-38">Dong (1979, figures 1–2)</a></cite>); those of oviraptorosaurs such as <i>Gigantoraptor</i>, 2.0 (measured from a photograph by MJW of referred specimen IGM 100/1002 of <i>Khaan mckennai</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-22" data-jats-ref-type="bibr" data-jats-rid="ref-22" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1671/0272-4634(2001)021[0209:TNOTOU]2.0.CO;2" title="Two new oviraptorids (Theropoda: Oviraptorosauria), Upper Cretaceous Djadokhta Formation, Ukhaa Tolgod, Mongolia" data-jats-ref-type="bibr" data-jats-rid="ref-22">Clark, Norell &amp; Barsbold, 2001</a></cite>). The very numerous vertebrae of <i>Elasmosaurus</i> are not very elongate, mostly having an EI around 1.0 and not exceeding about 1.4 (measured from <cite itemprop="citation" itemscope="itemscope" itemref="ref-116" data-jats-ref-type="bibr" data-jats-rid="ref-116" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Redescription of Elasmosaurus platyurus Cope, 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (Lower Campanian) of Kansas, U.S.A&quot;" title="Redescription of Elasmosaurus platyurus Cope, 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (Lower Campanian) of Kansas, U.S.A" data-jats-ref-type="bibr" data-jats-rid="ref-116">Sachs (2005)</a></cite>, figure 4).</p>
+          <figure class="fig" id="fig-7">
+            <div class="image-container">
+              <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-7-2x.jpg" title="View the full image" class="fresco" data-fresco-caption="Figure 7: Disparity of sauropod cervical vertebrae." data-fresco-group="figure" data-fresco-options="fit: 'width', ui: 'outside', thumbnails: false, loop: true, position: true, preload: false">
+                <img class="graphic" src="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-7-1x.jpg" data-image-id="fig-7" alt="Disparity of sauropod cervical vertebrae." data-full="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-7-full.png" data-thumb="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-7-thumb.jpg" data-original="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-7.png" data-image-type="figure" data-jats-mimetype="image" data-jats-mime-subtype="png"/>
+              </a>
+            </div>
+            <figcaption>
+              <h4 class="heading"><span class="caption-label">Figure 7: </span>Disparity of sauropod cervical vertebrae.</h4>
+              <span class="p">1, <i>Apatosaurus</i> “<i>laticollis</i>” <cite itemprop="citation" itemscope="itemscope" itemref="ref-82" data-jats-ref-type="bibr" data-jats-rid="ref-82" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Principal characters of American Jurassic dinosaurs, Part II&quot;" title="Principal characters of American Jurassic dinosaurs, Part II" data-jats-ref-type="bibr" data-jats-rid="ref-82">Marsh, 1879b</a></cite> holotype YPM 1861, cervical ?13, now referred to <i>Apatosaurus ajax</i> (see <cite itemprop="citation" itemscope="itemscope" itemref="ref-88" data-jats-ref-type="bibr" data-jats-rid="ref-88" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Remarks on the North American sauropod Apatosaurus Marsh&quot;" title="Remarks on the North American sauropod Apatosaurus Marsh" data-jats-ref-type="bibr" data-jats-rid="ref-88">McIntosh, 1995</a></cite>), in posterior and left lateral views, after <cite itemprop="citation" itemscope="itemscope" itemref="ref-107" data-jats-ref-type="bibr" data-jats-rid="ref-107" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Marsh’s dinosaurs: the collections from como bluff&quot;" title="Marsh’s dinosaurs: the collections from como bluff" data-jats-ref-type="bibr" data-jats-rid="ref-107">Ostrom &amp; McIntosh (1966, plate 15)</a></cite>; the portion reconstructed in plaster (<cite itemprop="citation" itemscope="itemscope" itemref="ref-5" data-jats-ref-type="bibr" data-jats-rid="ref-5" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1086/275121" title="Scientific news: 5. Notes on the Paleontological Laboratory of the United States Geological Survey under Professor Marsh" data-jats-ref-type="bibr" data-jats-rid="ref-5">Barbour, 1890, figure 1</a></cite>) is grayed out in posterior view; lateral view reconstructed after <i>Apatosaurus louisae</i> (<cite itemprop="citation" itemscope="itemscope" itemref="ref-50" data-jats-ref-type="bibr" data-jats-rid="ref-50" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Osteology of Apatosaurus, with special reference to specimens in the Carnegie Museum&quot;" title="Osteology of Apatosaurus, with special reference to specimens in the Carnegie Museum" data-jats-ref-type="bibr" data-jats-rid="ref-50">Gilmore, 1936</a></cite>, plate XXIV). 2, “<i>Brontosaurus excelsus</i>” <cite itemprop="citation" itemscope="itemscope" itemref="ref-81" data-jats-ref-type="bibr" data-jats-rid="ref-81" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Notice of new Jurassic reptiles&quot;" title="Notice of new Jurassic reptiles" data-jats-ref-type="bibr" data-jats-rid="ref-81">Marsh, 1879a</a></cite> holotype YPM 1980, cervical 8, now referred to <i>Apatosaurus excelsus</i> (see <cite itemprop="citation" itemscope="itemscope" itemref="ref-114" data-jats-ref-type="bibr" data-jats-rid="ref-114" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Structure and relationships of opisthocoelian dinosaurs. Part I, Apatosaurus Marsh&quot;" title="Structure and relationships of opisthocoelian dinosaurs. Part I, Apatosaurus Marsh" data-jats-ref-type="bibr" data-jats-rid="ref-114">Riggs, 1903</a></cite>), in anterior and left lateral views, after <cite itemprop="citation" itemscope="itemscope" itemref="ref-107" data-jats-ref-type="bibr" data-jats-rid="ref-107" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Marsh’s dinosaurs: the collections from como bluff&quot;" title="Marsh’s dinosaurs: the collections from como bluff" data-jats-ref-type="bibr" data-jats-rid="ref-107">Ostrom &amp; McIntosh (1966, plate 12)</a></cite>; lateral view reconstructed after <i>Apatosaurus louisae</i> (<cite itemprop="citation" itemscope="itemscope" itemref="ref-50" data-jats-ref-type="bibr" data-jats-rid="ref-50" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Osteology of Apatosaurus, with special reference to specimens in the Carnegie Museum&quot;" title="Osteology of Apatosaurus, with special reference to specimens in the Carnegie Museum" data-jats-ref-type="bibr" data-jats-rid="ref-50">Gilmore, 1936</a></cite>, plate XXIV). 3, “<i>Titanosaurus</i>” <i>colberti</i> <cite itemprop="citation" itemscope="itemscope" itemref="ref-60" data-jats-ref-type="bibr" data-jats-rid="ref-60" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1080/02724634.1997.10010958" title="New titanosaurid (Dinosauria: Sauropoda) from the Late Cretaceous of Central India" data-jats-ref-type="bibr" data-jats-rid="ref-60">Jain &amp; Bandyopadhyay, 1997</a></cite> holotype ISIR 335/2, mid-cervical vertebra, now referred to <i>Isisaurus</i> (See <cite itemprop="citation" itemscope="itemscope" itemref="ref-150" data-jats-ref-type="bibr" data-jats-rid="ref-150" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1017/S1477201903001044" title="A revision of Titanosaurus Lydekker (Dinosauria – Sauropoda), the first dinosaur genus with a ‘Gondwanan’ distribution" data-jats-ref-type="bibr" data-jats-rid="ref-150">Wilson &amp; Upchurch, 2003</a></cite>), in posterior and left lateral views, after <cite itemprop="citation" itemscope="itemscope" itemref="ref-60" data-jats-ref-type="bibr" data-jats-rid="ref-60" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1080/02724634.1997.10010958" title="New titanosaurid (Dinosauria: Sauropoda) from the Late Cretaceous of Central India" data-jats-ref-type="bibr" data-jats-rid="ref-60">Jain &amp; Bandyopadhyay (1997, figure 4)</a></cite>. 4, “<i>Brachiosaurus</i>” <i>brancai</i> paralectotype MB.R.2181, cervical 8, now referred to <i>Giraffatitan</i> (see <cite itemprop="citation" itemscope="itemscope" itemref="ref-129" data-jats-ref-type="bibr" data-jats-rid="ref-129" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1671/039.029.0309" title="A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensch 1914)" data-jats-ref-type="bibr" data-jats-rid="ref-129">Taylor, 2009</a></cite>), in posterior and left lateral views, modified from <cite itemprop="citation" itemscope="itemscope" itemref="ref-64" data-jats-ref-type="bibr" data-jats-rid="ref-64" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Die Wirbelsaule von Brachiosaurus brancai&quot;" title="Die Wirbelsaule von Brachiosaurus brancai" data-jats-ref-type="bibr" data-jats-rid="ref-64">Janensch (1950, figures 43–46)</a></cite>. 5, <i>Erketu ellisoni</i> holotype IGM 100/1803, cervical 4 in anterior and left lateral views, modified from <cite itemprop="citation" itemscope="itemscope" itemref="ref-68" data-jats-ref-type="bibr" data-jats-rid="ref-68" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1206/0003-0082(2006)3508[1:EEALSF]2.0.CO;2" title="Erketu ellisoni, a long-necked sauropod from Bor Guve (Dornogov Aimag, Mongolia)" data-jats-ref-type="bibr" data-jats-rid="ref-68">Ksepka &amp; Norell (2006, figures 5a–d)</a></cite>.</span>
+              <div class="article-image-download">
+                <a href="//dfzljdn9uc3pi.cloudfront.net/2013/36/1/fig-7-full.png" class="btn btn-mini" download="peerj-36-fig-7.png"><i class="icon-picture"> </i> Download full-size image</a>
+              </div>
+              <div class="object-id article-component-doi">DOI: <a href="http://dx.doi.org/10.7717/peerj.36/fig-7" rel="tooltip" title="Cite this object using this DOI">10.7717/peerj.36/fig-7</a></div>
+            </figcaption>
+          </figure>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Air-sac system</h3>
+          <p>One limiting factor on neck length is the difficulty of breathing through a long trachea. If the trachea is narrow, then it is difficult to inhale sufficient air quickly – a problem exacerbated by friction of inhaled air against the tracheal wall. But if the trachea is wider, its volume is increased, and a larger quantity of used air in the “tracheal dead space” is re-inhaled in each breath, reducing the oxygen content of each breath.</p>
+          <p>For this reason, it would be reasonable to expect animals to evolve the shortest possible trachea. However, in one clade – birds – an elongate trachea is not unusual, having evolved in swans (<cite itemprop="citation" itemscope="itemscope" itemref="ref-4" data-jats-ref-type="bibr" data-jats-rid="ref-4" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;The trumpeter swan&quot;" title="The trumpeter swan" data-jats-ref-type="bibr" data-jats-rid="ref-4">Banko, 1960</a></cite>), cranes (<cite itemprop="citation" itemscope="itemscope" itemref="ref-66" data-jats-ref-type="bibr" data-jats-rid="ref-66" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Cranes of the world&quot;" title="Cranes of the world" data-jats-ref-type="bibr" data-jats-rid="ref-66">Johnsgard, 1983</a></cite>), moas (<cite itemprop="citation" itemscope="itemscope" itemref="ref-155" data-jats-ref-type="bibr" data-jats-rid="ref-155" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;The lost world of the moa&quot;" title="The lost world of the moa" data-jats-ref-type="bibr" data-jats-rid="ref-155">Worthy &amp; Holdaway, 2002</a></cite>), birds-of-paradise (<cite itemprop="citation" itemscope="itemscope" itemref="ref-44" data-jats-ref-type="bibr" data-jats-rid="ref-44" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.2307/1369335" title="Adaptive significance of tracheal elongation in manucodes (Paradisaeidae)" data-jats-ref-type="bibr" data-jats-rid="ref-44">Frith, 1994</a></cite>) and several other groups. This trend reaches its peak in the trumpet manucode <i>Phonygammus keraudrrenii</i> (<cite itemprop="citation" itemscope="itemscope" itemref="ref-23" data-jats-ref-type="bibr" data-jats-rid="ref-23" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.2307/1367193" title="Tracheal elongation in birds-of-paradise" data-jats-ref-type="bibr" data-jats-rid="ref-23">Clench, 1978</a></cite>). In some mature males, the trachea coils back on itself so many times that its total length exceeds 800 mm, nearly three times the total body length of approx. 30 cm. Alone among extant animals, birds are able to cope with such extreme tracheal elongation, due to their very efficient lungs and the large tidal volume of the whole respiratory system on account of the voluminous air-sacs.</p>
+          <p>It is now well established that sauropods had an air-sac system similar to that of extant birds (<cite itemprop="citation" itemscope="itemscope" itemref="ref-139" data-jats-ref-type="bibr" data-jats-rid="ref-139" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1666/0094-8373(2003)029&lt;0243:VPASAT&gt;2.0.CO;2" title="Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs" data-jats-ref-type="bibr" data-jats-rid="ref-139">Wedel, 2003</a></cite>), and most likely a similarly efficient flow-through lung (<cite itemprop="citation" itemscope="itemscope" itemref="ref-145" data-jats-ref-type="bibr" data-jats-rid="ref-145" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1002/jez.513" title="Evidence for bird-like air sacs in saurischian dinosaurs" data-jats-ref-type="bibr" data-jats-rid="ref-145">Wedel, 2009</a></cite>). These features would have greatly eased the problem of tracheal dead space, facilitating the evolution of longer necks. The air-sac system, including cervical air-sacs and extensive cervical diverticula running the full length of the neck, would also have served to lighten long necks.</p>
+          <p>Among other long-necked animals, theropods (including <i>Therizinosaurus</i> and <i>Gigantoraptor</i>) and pterosaurs also had air-sac systems; but the mammals (giraffes, <i>Paraceratherium</i>) did not. However, whales provide an example suggesting it is unlikely that the evolution of long necks in terrestrial mammals has been limited by tracheal dead space. In a male sperm whale (<i>Physeter</i>) with a total body length of 16 m, the length of the head is 5.6 m (<cite itemprop="citation" itemscope="itemscope" itemref="ref-97" data-jats-ref-type="bibr" data-jats-rid="ref-97" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Change of form in the sperm whale accompanied with growth&quot;" title="Change of form in the sperm whale accompanied with growth" data-jats-ref-type="bibr" data-jats-rid="ref-97">Nishiwaki, Ohsumi &amp; Maeda (1963)</a></cite>, cited in <cite itemprop="citation" itemscope="itemscope" itemref="ref-29" data-jats-ref-type="bibr" data-jats-rid="ref-29" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1111/j.1748-7692.1999.tb00882.x" title="The sperm whale’s nose: sexual selection on a grand scale?" data-jats-ref-type="bibr" data-jats-rid="ref-29">Cranford</a></cite> (<cite itemprop="citation" itemscope="itemscope" itemref="ref-29" data-jats-ref-type="bibr" data-jats-rid="ref-29" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1111/j.1748-7692.1999.tb00882.x" title="The sperm whale’s nose: sexual selection on a grand scale?" data-jats-ref-type="bibr" data-jats-rid="ref-29">1999</a></cite>, table 1)). The largest sperm whales are up to 20 m in total body length (<cite itemprop="citation" itemscope="itemscope" itemref="ref-52" data-jats-ref-type="bibr" data-jats-rid="ref-52" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;The sperm whale&quot;" title="The sperm whale" data-jats-ref-type="bibr" data-jats-rid="ref-52">Gosho, Rice &amp; Breiwick, 1984</a></cite>), which would give a head length of 7 m if these largest individuals scaled isometrically with the 16-m whales. However, the head length of sperm whales is positively allometric and increases with age even in adults (<cite itemprop="citation" itemscope="itemscope" itemref="ref-29" data-jats-ref-type="bibr" data-jats-rid="ref-29" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1111/j.1748-7692.1999.tb00882.x" title="The sperm whale’s nose: sexual selection on a grand scale?" data-jats-ref-type="bibr" data-jats-rid="ref-29">Cranford, 1999</a></cite>, p. 1141 and figure 4), so a 20-m adult might well have a head slightly more than 7 m long. As in all cetaceans, the skull of a sperm whale is separated from the ribcage by the highly compressed cervical series. Finally, the nasal airways in sperm whales do not take a direct path from the blowhole to the lungs but describe sinuous curves through the head (<cite itemprop="citation" itemscope="itemscope" itemref="ref-29" data-jats-ref-type="bibr" data-jats-rid="ref-29" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1111/j.1748-7692.1999.tb00882.x" title="The sperm whale’s nose: sexual selection on a grand scale?" data-jats-ref-type="bibr" data-jats-rid="ref-29">Cranford, 1999</a></cite>, figures 1 and 3). In a sperm whale with a 7-m head, the internal convolution of the nasal airways and the addition of the trachea spanning from the head to the trunk would give the path from blowhole to lungs a total length of perhaps 9 m, showing that tracheae at least that long are possible without an air sac system.</p>
+        </section>
+        <section class="sec">
+          <h3 class="heading">Vertebral architecture</h3>
+          <p>Aside from the factors previously discussed, the elongation of sauropod necks was made possible by the distinctive architecture of their cervical vertebrae. The various aspects of their architecture are discussed in detail in the next section.</p>
+        </section>
+      </section>
+      <section class="sec">
+        <h2 class="heading">Architecture of Sauropod Necks</h2>
+        <section class="sec">
+          <h3 class="heading">Pneumaticity of cervical vertebrae</h3>
+          <p>Not only did sauropods have a soft-tissue diverticular system, but the diverticula often invaded the vertebrae, leaving extensive excavations and other traces (e.g., <cite itemprop="citation" itemscope="itemscope" itemref="ref-63" data-jats-ref-type="bibr" data-jats-rid="ref-63" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien&quot;" title="Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien" data-jats-ref-type="bibr" data-jats-rid="ref-63">Janensch, 1947</a></cite>; <cite itemprop="citation" itemscope="itemscope" itemref="ref-148" data-jats-ref-type="bibr" data-jats-rid="ref-148" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon&quot;" title="Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon" data-jats-ref-type="bibr" data-jats-rid="ref-148">Wedel, Cifelli &amp; Sanders, 2000b</a></cite>). Indeed, it is from the latter that we are able to infer the former.</p>
+          <p>The air space proportion (ASP) of a bone is the proportion of its volume taken up by pneumatic cavities (<cite itemprop="citation" itemscope="itemscope" itemref="ref-140" data-jats-ref-type="bibr" data-jats-rid="ref-140" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates&quot;" title="Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates" data-jats-ref-type="bibr" data-jats-rid="ref-140">Wedel, 2005</a></cite>). Dicraeosaurids (<i>Dicraeosaurus</i>, <i>Amargasaurus</i>, and related taxa) had reduced postcranial pneumaticity compared to other neosauropods, both in terms of the number of presacral vertebrae that were pneumatized, and in the air space proportion (<cite itemprop="citation" itemscope="itemscope" itemref="ref-118" data-jats-ref-type="bibr" data-jats-rid="ref-118" itemtype="http://schema.org/ScholarlyArticle"><a class="xref xref-bibr" href="http://dx.doi.org/10.1007/s00015-006-1177-x" title="Pneumatic structures in the cervical vertebrae of the Late Jurassic Tendaguru sauropods Brachiosaurus brancai and Dicraeosaurus" data-jats-ref-type="bibr" data-jats-rid="ref-118">Schwarz &amp; Fritsch, 2006</a></cite>). The presacral vertebrae of most neosauropod taxa had ASPs between 0.50 and 0.70 (<a class="xref xref-table" href="#table-2" data-jats-ref-type="table" data-jats-rid="table-2">Table 2</a>) – as lightly built as the pneumatic bones of most birds (<cite itemprop="citation" itemscope="itemscope" itemref="ref-140" data-jats-ref-type="bibr" data-jats-rid="ref-140" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates&quot;" title="Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates" data-jats-ref-type="bibr" data-jats-rid="ref-140">Wedel, 2005</a></cite>). Basal sauropods outside or near the base of Neosauropoda, such as <i>Cetiosaurus</i>, <i>Jobaria</i>, and <i>Haplocanthosaurus</i>, had much lower ASPs, around 0.40. (ASPs of <i>Cetiosaurus</i> and <i>Jobaria</i> are estimates based on personal observations of the holotypes and referred specimens, and comparisons to CT scans of similarly-constructed <i>Haplocanthosaurus</i> vertebrae.)</p>
+          <div class="table-wrap" id="table-2">
+            <div class="caption">
+              <span class="caption-label">Table 2: </span>
+              <div class="title">Air Space Proportion (ASP) of sections through sauropod vertebrae.</div>
+              <span class="p">Measurements are taken from CT sections, photographs, and published images. Sections are transverse unless otherwise noted. Although this dataset is almost three times as large as that reported by <cite itemprop="citation" itemscope="itemscope" itemref="ref-140" data-jats-ref-type="bibr" data-jats-rid="ref-140" itemtype="http://schema.org/Book"><a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates&quot;" title="Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates" data-jats-ref-type="bibr" data-jats-rid="ref-140">Wedel (2005)</a></cite>, the mean is the about same, 0.61 compared to 0.60. Abbreviations: C, cervical; Cd, caudal; D, dorsal; P, presacral.</span>
+            </div>
+            <div class="table-container">
+              <table>
+                <colgroup>
+                  <col align="left"/>
+                  <col align="left"/>
+                  <col align="left"/>
+                  <col align="left"/>
+                  <col align="left"/>
+                </colgroup>
+                <thead>
+                  <tr>
+                    <th style="text-align:left;">
+                      <b>Taxon</b>
+                    </th>
+                    <th style="text-align:left;">
+                      <b>Region</b>
+                    </th>
+                    <th style="text-align:left;"/>
+                    <th style="text-align:left;">
+                      <b>ASP</b>
+                    </th>
+                    <th style="text-align:left;">
+                      <b>Source</b>
+                    </th>
+                  </tr>
+                </thead>
+                <tbody>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Apatosaurus</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.69</td>
+                    <td style="text-align:left;">OMNH 01094</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.52</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">posterior centrum</td>
+                    <td style="text-align:left;">0.73</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">cotyle</td>
+                    <td style="text-align:left;">0.32</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.63</td>
+                    <td style="text-align:left;">OMNH 01340</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.69</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">cotyle</td>
+                    <td style="text-align:left;">0.49</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.52</td>
+                    <td style="text-align:left;">CM 555 C6</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.75</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">posterior centrum</td>
+                    <td style="text-align:left;">0.59</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">cotyle</td>
+                    <td style="text-align:left;">0.34</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">parapophysis</td>
+                    <td style="text-align:left;">0.6</td>
+                    <td style="text-align:left;">BYU 11998</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">cotyle</td>
+                    <td style="text-align:left;">0.7</td>
+                    <td style="text-align:left;">BYU 11889</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Brachiosaurus</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.55</td>
+                    <td style="text-align:left;">BYU 12866</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.67</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">posterior centrum</td>
+                    <td style="text-align:left;">0.81</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">Brachiosauridae</td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.89</td>
+                    <td style="text-align:left;">MIWG 7306</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">P</td>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">0.65</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-96" data-jats-ref-type="bibr" data-jats-rid="ref-96" itemtype="http://schema.org/Book">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Saurischian dinosaurs 1: Sauropods&quot;" title="Saurischian dinosaurs 1: Sauropods" data-jats-ref-type="bibr" data-jats-rid="ref-96">Naish &amp; Martill (2001, plate 32)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">P</td>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">0.85</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-96" data-jats-ref-type="bibr" data-jats-rid="ref-96" itemtype="http://schema.org/Book">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Saurischian dinosaurs 1: Sauropods&quot;" title="Saurischian dinosaurs 1: Sauropods" data-jats-ref-type="bibr" data-jats-rid="ref-96">Naish &amp; Martill (2001, plate 33)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">P</td>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">0.85</td>
+                    <td style="text-align:left;">MIWG uncatalogued</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Camarasaurus</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.51</td>
+                    <td style="text-align:left;">OMNH 01109</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.68</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">cotyle</td>
+                    <td style="text-align:left;">0.54</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.49</td>
+                    <td style="text-align:left;">OMNH 01313</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.52</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">cotyle</td>
+                    <td style="text-align:left;">0.5</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">D</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.58</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-107" data-jats-ref-type="bibr" data-jats-rid="ref-107" itemtype="http://schema.org/Book">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Marsh’s dinosaurs: the collections from como bluff&quot;" title="Marsh’s dinosaurs: the collections from como bluff" data-jats-ref-type="bibr" data-jats-rid="ref-107">Ostrom &amp; McIntosh (1966, plate 23)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">D</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.63</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-107" data-jats-ref-type="bibr" data-jats-rid="ref-107" itemtype="http://schema.org/Book">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Marsh’s dinosaurs: the collections from como bluff&quot;" title="Marsh’s dinosaurs: the collections from como bluff" data-jats-ref-type="bibr" data-jats-rid="ref-107">Ostrom &amp; McIntosh (1966, plate 23)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">D</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.71</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-107" data-jats-ref-type="bibr" data-jats-rid="ref-107" itemtype="http://schema.org/Book">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Marsh’s dinosaurs: the collections from como bluff&quot;" title="Marsh’s dinosaurs: the collections from como bluff" data-jats-ref-type="bibr" data-jats-rid="ref-107">Ostrom &amp; McIntosh (1966, plate 23)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Chondrosteosaurus</i>
+                    </td>
+                    <td style="text-align:left;">P</td>
+                    <td style="text-align:left;">centrum (horiz.)</td>
+                    <td style="text-align:left;">0.7</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-96" data-jats-ref-type="bibr" data-jats-rid="ref-96" itemtype="http://schema.org/Book">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Saurischian dinosaurs 1: Sauropods&quot;" title="Saurischian dinosaurs 1: Sauropods" data-jats-ref-type="bibr" data-jats-rid="ref-96">Naish &amp; Martill (2001, figure 8.5)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Diplodocus</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.56</td>
+                    <td style="text-align:left;">BYU 12613</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.54</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">posterior centrum</td>
+                    <td style="text-align:left;">0.66</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Giraffatitan</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.73</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-64" data-jats-ref-type="bibr" data-jats-rid="ref-64" itemtype="http://schema.org/ScholarlyArticle">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Die Wirbelsaule von Brachiosaurus brancai&quot;" title="Die Wirbelsaule von Brachiosaurus brancai" data-jats-ref-type="bibr" data-jats-rid="ref-64">Janensch (1950, figure 70)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle (sagittal)</td>
+                    <td style="text-align:left;">0.57</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-63" data-jats-ref-type="bibr" data-jats-rid="ref-63" itemtype="http://schema.org/ScholarlyArticle">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien&quot;" title="Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien" data-jats-ref-type="bibr" data-jats-rid="ref-63">Janensch (1947, figure 4)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">D</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.59</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-63" data-jats-ref-type="bibr" data-jats-rid="ref-63" itemtype="http://schema.org/ScholarlyArticle">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien&quot;" title="Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien" data-jats-ref-type="bibr" data-jats-rid="ref-63">Janensch (1947, figure 2)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Haplocanthosaurus</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.39</td>
+                    <td style="text-align:left;">CM 879-7</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.56</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">posterior centrum</td>
+                    <td style="text-align:left;">0.42</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">cotyle</td>
+                    <td style="text-align:left;">0.28</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">D</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.36</td>
+                    <td style="text-align:left;">CM 572</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Malawisaurus</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.56</td>
+                    <td style="text-align:left;">MAL-280-1</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.62</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">condyle</td>
+                    <td style="text-align:left;">0.57</td>
+                    <td style="text-align:left;">MAL-280-4</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.56</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Phuwiangosaurus</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.55</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-86" data-jats-ref-type="bibr" data-jats-rid="ref-86" itemtype="http://schema.org/ScholarlyArticle">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Baby sauropods from the Sao Khua Formation (Lower Cretaceous) in Northeastern Thailand&quot;" title="Baby sauropods from the Sao Khua Formation (Lower Cretaceous) in Northeastern Thailand" data-jats-ref-type="bibr" data-jats-rid="ref-86">Martin (1994, figure 2)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Pleurocoelus</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.55</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-77" data-jats-ref-type="bibr" data-jats-rid="ref-77" itemtype="http://schema.org/ScholarlyArticle">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Systematic Paleontology, Lower Cretaceous: Vertebrata&quot;" title="Systematic Paleontology, Lower Cretaceous: Vertebrata" data-jats-ref-type="bibr" data-jats-rid="ref-77">Lull (1911, plate 15)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Saltasaurus</i>
+                    </td>
+                    <td style="text-align:left;">D</td>
+                    <td style="text-align:left;">centrum (horiz.)</td>
+                    <td style="text-align:left;">0.62</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-112" data-jats-ref-type="bibr" data-jats-rid="ref-112" itemtype="http://schema.org/Book">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Osteología de Saltasaurus loricatus (Sauropoda–Titanosauridae) del Cretácico Superior del Noroeste Argentino&quot;" title="Osteología de Saltasaurus loricatus (Sauropoda–Titanosauridae) del Cretácico Superior del Noroeste Argentino" data-jats-ref-type="bibr" data-jats-rid="ref-112">Powell (1992, figure 16)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.55</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">neural spine (horiz.)</td>
+                    <td style="text-align:left;">0.82</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">D</td>
+                    <td style="text-align:left;">prezygapophysis</td>
+                    <td style="text-align:left;">0.78</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-112" data-jats-ref-type="bibr" data-jats-rid="ref-112" itemtype="http://schema.org/Book">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Osteología de Saltasaurus loricatus (Sauropoda–Titanosauridae) del Cretácico Superior del Noroeste Argentino&quot;" title="Osteología de Saltasaurus loricatus (Sauropoda–Titanosauridae) del Cretácico Superior del Noroeste Argentino" data-jats-ref-type="bibr" data-jats-rid="ref-112">Powell (1992, figure 16)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Sauroposeidon</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">prezyg. ramus</td>
+                    <td style="text-align:left;">0.89</td>
+                    <td style="text-align:left;">OMNH 53062</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">postzygapophysis</td>
+                    <td style="text-align:left;">0.74</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">anterior centrum</td>
+                    <td style="text-align:left;">0.75</td>
+                    <td style="text-align:left;">,,</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Supersaurus</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.64</td>
+                    <td style="text-align:left;">WDC-DMJ021</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">
+                      <i>Tornieria</i>
+                    </td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.56</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-63" data-jats-ref-type="bibr" data-jats-rid="ref-63" itemtype="http://schema.org/ScholarlyArticle">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien&quot;" title="Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien" data-jats-ref-type="bibr" data-jats-rid="ref-63">Janensch (1947, figure 8)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">posterior centrum</td>
+                    <td style="text-align:left;">0.77</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-63" data-jats-ref-type="bibr" data-jats-rid="ref-63" itemtype="http://schema.org/ScholarlyArticle">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien&quot;" title="Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien" data-jats-ref-type="bibr" data-jats-rid="ref-63">Janensch (1947, figure 3)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">D</td>
+                    <td style="text-align:left;">condyle (sagittal)</td>
+                    <td style="text-align:left;">0.78</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-63" data-jats-ref-type="bibr" data-jats-rid="ref-63" itemtype="http://schema.org/ScholarlyArticle">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien&quot;" title="Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien" data-jats-ref-type="bibr" data-jats-rid="ref-63">Janensch (1947, figure 9)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">Cd</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.47</td>
+                    <td style="text-align:left;">
+                      <cite itemprop="citation" itemscope="itemscope" itemref="ref-63" data-jats-ref-type="bibr" data-jats-rid="ref-63" itemtype="http://schema.org/ScholarlyArticle">
+                        <a class="xref xref-bibr" href="http://scholar.google.com/scholar?q=intitle:&quot;Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien&quot;" title="Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien" data-jats-ref-type="bibr" data-jats-rid="ref-63">Janensch (1947, figure 7)</a>
+                      </cite>
+                    </td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;">Sauropoda indet.</td>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.54</td>
+                    <td style="text-align:left;">OMNH 01866</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">posterior centrum</td>
+                    <td style="text-align:left;">0.46</td>
+                    <td style="text-align:left;">OMNH 01867</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;">C</td>
+                    <td style="text-align:left;">mid-centrum</td>
+                    <td style="text-align:left;">0.55</td>
+                    <td style="text-align:left;">OMNH 01882</td>
+                  </tr>
+                  <tr>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                    <td style="text-align:left;"/>
+                  </tr>
+                  <tr>