Editing Quetzalcoatlus (section)

==Description==
[[File:Quetzalcoatlus northropi.png|thumb|Speculative [[life reconstruction]] of ''Q. northropi'']]
''Quetzalcoatlus northropi'' was among the largest azhdarchids, though was rivalled in size by ''Arambourgiania'' and ''[[Hatzegopteryx]]''<ref name="padian2021" /><ref name="Paul-2022" /> (and possibly ''[[Cryodrakon]]'').<ref name="Paul-2022" /> Azhdarchids were split into two primary categories: short-necked taxa with short, robust beaks (i.e. ''Hatzegopteryx''<ref name=":0">{{Cite journal |last1=Naish |first1=Darren |last2=Witton |first2=Mark P. |date=January 18, 2017 |title=Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators |journal=PeerJ |language=en |volume=5 |pages=e2908 |doi=10.7717/peerj.2908 |doi-access=free |pmid=28133577 |pmc=5248582 |issn=2167-8359}}</ref> and ''Wellnhopterus''), and long-necked taxa with longer, slenderer beaks (i.e. ''[[Zhejiangopterus]]''). Of these, ''Quetzalcoatlus'' falls squarely into the latter.<ref name=":1">{{Cite book |last=Witton |first=Mark P. |title=Pterosaurs: natural history, evolution, anatomy |date=2013 |publisher=Princeton University Press |isbn=978-0-691-15061-1 |location=Princeton}}</ref> Based on the limb morphology of ''Q. lawsoni'', related azhdarchids such as ''Zhejiangopterus'', and pterosaurs at large, in addition to [[Haenamichnus|azhdarchid tracks]] from South Korea, ''Quetzalcoatlus'' was likely [[Quadrupedalism|quadrupedal]].<ref name="witton&naish2008" /><ref name="wittonweight2010">{{cite journal |last1=Witton |first1=Mark P. |last2=Habib |first2=Michael B. |last3=Laudet |first3=Vincent |year=2010 |title=On the size and flight diversity of giant pterosaurs, the use of birds as pterosaur analogues and comments on pterosaur flightlessness |journal=PLOS ONE |volume=5 |issue=11 |page=e13982 |bibcode=2010PLoSO...513982W |doi=10.1371/journal.pone.0013982 |pmc=2981443 |pmid=21085624 |doi-access=free}}</ref><ref name="padian2021" /> As a pterosaur, ''Quetzalcoatlus'' would have been covered in hair-like [[Pterosaur|pycnofibres]], and had extensive [[Patagium|wing-membranes]], which would have been distended by a long wing-finger.<ref name=":1" /> There have been various models of the morphology of pterodactyloid wings,<ref name="padian2021" /> though based on multiple well-preserved pterosaur specimens, it is likely that azhdarchids had broad wings, with a [[Patagium|brachiopatagium]] extending down to the ankle. The [[aspect ratio]] of azhdarchid wings is 8.1, similar to that of [[stork]]s and [[Bird of prey|birds of prey]] that engage in static soaring (relying on [[air current]]s to gain altitude and remain aloft).<ref name="witton&naish2008" />

===Size===
{{See also|Pterosaur size}}
[[File:Quetzalcoatlus Size Comparison.svg|thumb|left|Size comparison of a human to ''Q. lawsoni'' (red) and ''Q. northropi'' (orange)]]
''Quetzalcoatlus'' is regarded as one of the [[Pterosaur size|largest pterosaurs]],<ref name="wittonweight2010" /> though its exact size has been difficult to determine. In 1975, Douglas Lawson compared the wing bones of ''Q. northropi'' to equivalent elements in ''[[Dsungaripterus]]'' and ''[[Pteranodon]]'' and suggested that it represented an individual with a wingspan of around {{cvt|15.5|m}}, or, alternatively, {{Convert|11|m|abbr=on}} or {{Convert|21|m|abbr=on}}.<ref name="lawson1975" /> Estimates put forward in subsequent years varied dramatically, ranging from {{Convert|5.2–25.8|m|ft|abbr=on}}, owing to differences in methodology.<ref name="andres2021" /> Among the supporters of the initial size estimates was [[Robert T. Bakker]], who, in his 1988 book ''[[The Dinosaur Heresies]]'', contended that ''Quetzalcoatlus'' may indeed have reached the upper estimates, and that it may have remained flighted by altering its method of flapping.<ref>{{Cite book |last=Bakker |first=Robert T. |author-link=Robert T. Bakker |title=The Dinosaur Heresies: new theories unlocking the mystery of the dinosaurs and their extinction |date=1986 |publisher=Morrow |isbn=978-0-688-04287-5 |edition=6.print. |location=New York}}</ref> Other estimates contemporary to Bakker's, however, consistently supported a smaller size of {{cvt|11|–|12|m}}.<ref name="andres2021" /> More recent estimates based on greater knowledge of azhdarchid proportions place its wingspan at {{cvt|10|–|11|m}}.<ref name="padian2021" /><ref name="Paul-2022" /><ref name="witton2010"/> This would approach the maximum size possible for azhdarchids, estimated at {{cvt|12|–|13|m}};<ref name=":1" /> while higher wingspans may technically be possible, they would require significant morphological changes,<ref name=":1" /> and the animal would struggle to become airborne due to increased strain on its joints and [[long bone]]s.<ref name=":7" /> In one paper from the 2021 Memoir which redescribed ''Quetzalcoatlus'', ''Q. lawsoni'' was estimated to have a wingspan of around {{Convert|4.5|m|ft|abbr=on}}.<ref name="andres2021" /> In 2022, [[Gregory S. Paul]] suggested that it had a somewhat larger wingspan of around {{cvt|5|m|ft}} and a body length, from beak to tail, of {{cvt|3.5|m|ft}}.<ref name="Paul-2022" /> Large azhdarchids such as ''Q. northropi'' have been estimated to have a shoulder height of about {{cvt|2–3|m|ft}},<ref>{{Cite journal |last=Witton |first=Mark P. |date=2008 |title=A new approach to determining pterosaur body mass and its implications for pterosaur flight |url=https://epub.ub.uni-muenchen.de/id/eprint/12010 |journal=Zitteliana |pages=143–158 |language=en |doi=10.5282/UBM/EPUB.12010}}</ref><ref name=":7">{{Cite journal |last=Witton |first=Mark P. |date=2010 |title=Pteranodon and beyond: the history of giant pterosaurs from 1870 onwards |url=https://www.lyellcollection.org/doi/10.1144/SP343.19 |journal=Geological Society, London, Special Publications |language=en |volume=343 |issue=1 |pages=313–323 |doi=10.1144/SP343.19 |bibcode=2010GSLSP.343..313W |issn=0305-8719}}</ref> and the head may have been held at a similar height to that of an extant giraffe.<ref name=":1" />

Body mass estimates for ''Quetzalcoatlus'' have, similarly, been historically variable. Mass estimates for giant azhdarchids are problematic because no existing species shares a similar size or body plan, and in consequence, published results vary widely.<ref name="witton&naish2008">{{cite journal|last1=Witton|first1=Mark P.|last2=Naish|first2=Darren|title=A Reappraisal of azhdarchid pterosaur functional morphology and paleoecology|journal=PLOS ONE|year=2008|volume=3|issue=5|page=e2271|doi=10.1371/journal.pone.0002271|pmid=18509539|pmc=2386974|doi-access=free|bibcode=2008PLoSO...3.2271W}}</ref> [[Crawford Greenewalt]] gave mass estimates of between {{Convert|30–440|kg|abbr=on}} for ''Q. northropi'', with the former figure assuming a small wingspan of {{Convert|5.2|m|abbr=on}}, and the latter assuming a far larger wingspan of {{Convert|15.4|m|abbr=on}}.<ref name="lawson1975b" /> In 2010, Donald M. Henderson recovered the body mass of ''Quetzalcoatlus'' at {{cvt|544|kg}}, twice that of other contemporary estimates, citing it as evidence for [[wikt:flightless|secondary flightlessness]] in the genus.<ref name="henderson2010" /> However, the vast majority of estimates published since the 2000s have hovered around {{cvt|200|-|250|kg}},<ref name="Paul2002">{{cite book |last=Paul |first=Gregory S. |url=https://archive.org/details/dinosaursofairev0000paul |title=Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds |publisher=Johns Hopkins University Press |year=2002 |isbn=0-8018-6763-0 |page=472 |url-access=registration}}</ref><ref name="wittonweight2010" /> due largely to a greater understanding of how aberrant the anatomy of azhdarchids was in comparison to other pterosaur clades.<ref name=":1" /> In 2021, Kevin Padian and colleagues estimated that ''Q. northropi'' would have weighed around {{cvt|150|kg|lb}}, and that ''Q. lawsoni'' would have weighed {{cvt|20|kg|lb}},<ref name="padian2021">{{cite journal|last1=Padian|first1=K.|last2=Cunningham|first2=J.R.|last3=Langston|first3=W. Jr.|last4=Conway|first4=J.|year=2021|title=Functional morphology of ''Quetzalcoatlus'' Lawson 1975 (Pterodactyloidea: Azhdarchoidea)|journal=Journal of Vertebrate Paleontology|volume=41|issue=sup1|pages=218–251|bibcode=2021JVPal..41S.218P|doi=10.1080/02724634.2020.1780247|s2cid=245125427|doi-access=free}}</ref> while a year later, Gregory S. Paul estimated a body mass of {{cvt|65|kg|lbs}} for the latter species.<ref name="Paul-2022">{{Cite book|last=Paul|first=Gregory S.|title=The Princeton Field Guide to Pterosaurs|year=2022|publisher=Princeton University Press|pages=161–162|doi=10.1515/9780691232218|isbn=9780691232218|s2cid=249332375}}</ref>

===Skull===
[[Image:Quetzskullswittonnaish2008.png|thumb|Skull reconstruction of ''Q. lawsoni'']]Complete skulls are not known from either ''Quetzalcoatlus'' species. Reconstructions of its skull anatomy must therefore draw from eight separate ''Q. lawsoni'' specimens which preserve skull elements. Based on the length of the mandible (lower jaw), the skull of ''Q. lawsoni'' likely measured about {{Convert|94–96|cm|in|abbr=on}} in length.<ref name="andres2021" /><ref name="kellner&langston1996" /> The distance between the [[Condyloid process|condyloid]] (articular) processes of the mandible is around {{Convert|13|cm|in|abbr=on}}.<ref name="padian2021" /> The ratio between the length of the skull and the length of the average dorsal (back) vertebra is very high in ''Q. lawsoni'', and is surpassed only by ''Pteranodon'' and ''[[Tupuxuara]]''.<ref name="andres2021" /> The nasoantorbital [[fenestra]], a massive opening found in many pterosaurs which combined the [[nasal cavity]] (which housed the external nostril) and [[antorbital fenestra]], was very large in ''Q. lawsoni'', occupying about a third of the total length of the skull.<ref name="andres2021" /><ref name="kellner&langston1996" /> In the largest specimen, TMM 41961-1.1, it measured {{Convert|34.7|cm|in|abbr=on}} in length and {{Convert|10.45|cm|in|abbr=on}} in height. ''Q. lawsoni''<nowiki/>'s [[choana]]e (internal nostrils) were [[wikt:confluent|confluent]] and anteriorly expanded, meaning that they were essentially fused and expanded towards the front. The orbit was small and [[wikt:obovate|obovate]], resembling an inverted egg in shape.<ref name="andres2021" /> It was fairly low on the skull, similar to other azhdarchoids, like [[Tapejaridae|tapejarids]].<ref name="kellner&langston1996" /> Like in other pterosaurs, the orbit was positioned in a way that would have allowed ''Quetzalcoatlus'' to see both forwards and directly to the sides, giving it a degree of [[Stereopsis|stereoscopic vision]].<ref name="padian2021" />

Like other azhdarchids, ''Quetzalcoatlus'' had a long, slender, toothless beak,<ref name="andres2021" /><ref name="kellner&langston1996" /> with a gape of around 52 degrees.<ref name="kellner&langston1996" /> It was constructed from the premaxilla and [[maxilla]] on the upper jaw,<ref name="andres2021" /> and the [[Mandible|dentary]] on the lower jaw.<ref name="kellner&langston1996" /> Beak tips are not preserved in any specimen, so it is not clear whether its tip was sharp or had some other morphology, such as a keel. The dentary had a slight [[wikt:sinusoidal|sinusoidal]] curve, which is also observed in ''[[Hatzegopteryx]]''.<ref name="andres2021" /> The [[mandibular symphysis|mandibular symphyses]] would have widened slightly as the jaw opened, slightly separating the mandibles, which has led to suggestions that some sort of [[Gular skin|gular pouch]] was present.<ref name="andres2021" /><ref name="kellner&langston1996" /> At the base of the beak, formed from the [[premaxilla]], was a crest, referred to by some authors as a [[sagittal crest]].<ref name="andres2021" /><ref name="kellner&langston1996" /> A premaxillary crest is also observed in ''Wellnhopterus'', though is smaller and more anterior. The exact form of the crest in ''Q. lawsoni'' has yet to be determined, due to the poor preservation of the rear half of ''Q. lawsoni''{{'}}s skull. From what is known, two distinct [[Polymorphism (biology)|morphotypes]] have been suggested: one with a square sagittal crest and a tall nasoantorbital [[fenestra]], and one with a more semicircular sagittal crest and a shorter nasoantorbital fenestra. Additionally, one morphotype is larger than the other, and has a proportionally shorter beak. Despite their differences, both share the diagnostic traits of ''Q. lawsoni'', and are considered the same species. The reason for there being two morphotypes is unclear, though it may correlate to individual variation, [[ontogeny]], or [[sexual dimorphism]].<ref name="andres2021" />

=== Skeleton ===
[[File:Azhdarchid pterosaur neck lengths.png|left|thumb|300x300px|Neck lengths of various azhdarchids. ''Q. sp.'' is now ''Q. lawsoni''.]]
Like other pterosaurs, ''Quetzalcoatlus'' had light, hollow bones, supported internally by struts called [[trabecula]]e. The neck of ''Q. lawsoni'', measured from the third [[Cervical vertebrae|cervical]] (neck) [[vertebra]] to the seventh, has been estimated at {{Convert|149.5|cm|in|abbr=on}}.<ref name=":0" /> It consisted of nine elongated vertebrae, which were [[wikt:procoelous|procoelous]], meaning that they were concave at the front.<ref name="andres2021" /> All of them were compressed [[Anatomical terms of location|dorsoventrally]] (top to bottom), and were better suited for dorsoventral motion than [[Anatomical terms of location|lateral]] (side-to-side) motion. However, the lateral range of motion was still extensive, and the neck and head could swing left and right in an arc of about 180 degrees.<ref name="padian2021" /><ref name="padian1983">{{Cite journal|author=Padian, K.|year=1983|title=A functional analysis of flying and walking in pterosaurs|journal=Paleobiology|volume=9|issue=3|pages=218–239|doi=10.1017/S009483730000765X|bibcode=1983Pbio....9..218P|s2cid=88434056}}</ref> Like in other azhdarchoids, the cervical vertebrae were low, with [[Vertebra|neural arches]] that were essentially inside the [[Vertebra|centrum]].<ref name=":1" /> In most azhdarchids, the [[Vertebra|neural spine]] of the seventh cervical vertebra was fairly long. This was not the case in ''Q. lawsoni'', where the neural spine was shorter.<ref name="andres2021" /> Internally, the cervical vertebrae were supported by trabeculae that increased their buckling load substantially (about 90%). This may have been an adaptation for counteracting [[shear force]]s exerted on the neck while in flight, though may have also enabled [[Agonistic behaviour|agonistic]] neck-bashing behaviors like those seen in [[giraffe]]s.<ref name=":2">{{Cite journal |last1=Williams |first1=Cariad J. |last2=Pani |first2=Martino |last3=Bucchi |first3=Andrea |last4=Smith |first4=Roy E. |last5=Kao |first5=Alexander |last6=Keeble |first6=William |last7=Ibrahim |first7=Nizar |last8=Martill |first8=David M. |date=April 23, 2021 |title=Helically arranged cross struts in azhdarchid pterosaur cervical vertebrae and their biomechanical implications |journal=iScience |volume=24 |issue=4 |pages=102338 |doi=10.1016/j.isci.2021.102338 |pmid=33997669 |pmc=8101050 |bibcode=2021iSci...24j2338W |issn=2589-0042}}</ref> While airborne, the neck of ''Q. northropi'' would have likely assumed a slight S-shaped curve, similar to swans.<ref name="padian2021" /> Similar to other azhdarchids, the torso was proportionally small, about half as long again as the [[humerus]].<ref name=":1" /><ref name="CW942">{{Cite journal |last1=Cai, Z. |last2=Wei, F. |name-list-style=amp |year=1994 |title=On a new pterosaur (''Zhejiangopterus linhaiensis'' gen. et sp. nov.) from Upper Cretaceous in Linhai, Zhejiang, China |url=http://paleoglot.org/files/Cai&Wei_94.pdf |journal=Vertebrata PalAsiatica |volume=32 |pages=181–194}}</ref> In ''Quetzalcoatlus'' specifically, the vertebrae at the base of the neck and the [[Shoulder girdle|pectoral girdle]] (shoulder girdle) are poorly known. The first four [[Dorsal vertebra|dorsal]] (back) vertebrae are fused into a [[notarium]],<ref name="andres2021" /> as in some other pterosaurs and birds,<ref>{{Cite journal |last1=Aires |first1=Alex Schiller |last2=Reichert |first2=Leici Machado |last3=Müller |first3=Rodrigo Temp |last4=Pinheiro |first4=Felipe Lima |last5=Andrade |first5=Marco Brandalise |date=2021 |title=Development and evolution of the notarium in Pterosauria |journal=Journal of Anatomy |language=en |volume=238 |issue=2 |pages=400–415 |doi=10.1111/joa.13319 |issn=0021-8782 |pmc=7812132 |pmid=33026119}}</ref> particularly ornithocheiroids.<ref name="andres2021" /> The vertebral count of the notarium is unlike ''[[Zhejiangopterus]]'', which had six notarial vertebrae, but like ''[[Azhdarcho]]''. Most other dorsal vertebrae are absent, except for three which had been integrated into the [[sacrum]]. Around seven dorsal vertebrae were free of the notarium and sacrum. Four true sacral vertebrae are preserved, though there were likely seven in all. No [[Tail|caudal]] (tail) vertebrae are preserved.<ref name="padian2021" />[[File:Pone.0013982.g003.png|thumb|250x250px|Holotype humerus of ''Q. northropi'' (A), alongside the humeri of ''Pteranodon'' (B) and ''Pterodactylus'' (C). The first two scale bars are 100 mm, whilst the third is 10 mm.]]
''Quetzalcoatlus''<nowiki/>' [[scapulocoracoid]], a fusion of the [[scapula]] and [[coracoid]], bones, was U-shaped and broad. Throughout azhdarchid evolution, the scapula had been reducing in length, and this reached its pinnacle in ''Q. lawsoni'', where the scapula was only slightly longer than the coracoid. The [[sternum]], like that of other pterosaurs, was broad. It had a transverse ridge on its posterior (rear) portion, also observed in ''Pteranodon'', albeit it is further forward in that genus.<ref name="andres2021" /> Like other pterosaurs, the bone walls of the sternum were very thin, and in the case of ''Q. lawsoni'', they were as little as {{Convert|1.5|mm|in|abbr=on}} thick.<ref>{{Cite journal |last=Hone |first=David W. E. |date=April 15, 2023 |title=The anatomy and diversity of the pterosaurian sternum |url=https://palaeo-electronica.org/content/2023/3813-the-sternum-of-pterosaurs |access-date=February 2, 2025 |journal=Palaeontologia Electronica |language=en |doi=10.26879/1261|doi-access=free }}</ref> ''Quetzalcoatlus'' and other azhdarchids have forelimb and hind limb proportions more similar to modern running [[ungulate]] mammals than to members of other pterosaur clades, implying that they were uniquely suited to a terrestrial lifestyle.<ref name="witton&naish2008" /> The [[humerus]] was short and robust, with considerable mobility.<ref name="padian2021" /> Its morphology differs somewhat between species, with ''Q. lawsoni''{{'}}s humerus having a proportionally shorter [[Humerus|deltopectoral crest]], and ''Q. northropi''{{'}}s being shaped more like a twisted hourglass. The [[ulna]] of ''Q. northropi'' was relatively shorter than that of ''Q. lawsoni'', measuring 1.36 times the length of the humerus, as opposed to 1.52 times the length of the humerus in ''Q. lawsoni'' and other azhdarchiforms.<ref name="andres2021" />  Like all pterosaurs, ''Quetzalcoatlus'' had a specialized [[Carpal bones|carpal]] (wrist) bone, the [[Pterosaur|pteroid]], which attached to the [[Sesamoid bone|sesamoid]] bone of the wrist. It faced inwards, pointing towards the deltopectoral crest, and supported the [[Patagium|propatagium]]. Specialized muscles allowed it to move slightly.<ref name="padian2021" /> The first digit is the smallest, and the third is the biggest, with the exception of the [[Pterosaur|wing finger]]. As with all pterosaurs, the wing finger was considerably longer than the others.<ref name="andres2021" /> It did not contact the ground, as evidenced by footprints. Whilst on land, it may have been held between the elbow and the torso.<ref name="padian2021" /> The wings were short and broad, and forelimb musclature was extensive. Flapping power came from several [[Skeletal muscle|muscle groups]] on the torso, forearm and [[Manus (anatomy)|manus]] (hand).<ref name="wittonweight2010" />

Typically for a pterosaur, the [[pelvis]] of ''Q. lawsoni'' consists of an [[Ilium (bone)|ilium]], [[Pubis (bone)|pubis]] and [[ischium]] that had fused into a single unit, articulating anteroventrally (towards the front, at the bottom) with the [[wikt:prepubis|prepubis]], a small bone that sat before the pubis and likely helped support the abdominal cavity during respiration.<ref name="andres2021" /> The [[pelvis]] of one ''Q. lawsoni'' specimen (TMM 41954-57) is large compared to that of other specimens, with deep posterior emargination and no preserved [[Pubic symphysis|symphisis]]. This suggests that ''Q. lawsoni'' exhibited sexual dimorphism, similar to that suggested for other [[monofenestrata]]ns (i.e. ''[[Darwinopterus]], [[Anhanguera (pterosaur)|Anhanguera]]'' and ''[[Nyctosaurus]]''). The [[femur]] was significantly more gracile than the humerus, though was still among the most robust bones in ''Quetzalcoatlus''{{'}} skeleton, judging by ''Q. lawsoni''.<ref name="padian2021" /> Based on ''Zhejiangopterus'', the humerus was around eighty percent of the length of the [[tibiotarsus]]. Azhdarchids overall had fairly narrow feet, no longer than 30% of the length of the [[tibia]],<ref name=":1" /> which may have borne fleshy pads similar to those of tapejarids.<ref name=":1" /><ref name="HHLUW022">{{cite journal |last1=Hwang |first1=K.G. |last2=Huh |first2=M. |last3=Lockley |first3=M. |last4=Unwin |first4=D. |last5=Wright |first5=J.L. |year=2002 |title=New pterosaur tracks (Pteraichnidae) from the Late Cretaceous Uhangri Formation, SW Korea |url=http://repository.geologyscience.ru/bitstream/handle/123456789/28316/Hwan_02.pdf?sequence=1&isAllowed=y |journal=Geological Magazine |volume=139 |issue=4 |pages=421–435 |doi=10.1017/S0016756802006647 |s2cid=54996027}}</ref> They were [[plantigrade]], meaning that they walked with the sole of the foot flat on the ground.<ref name="andres2021" /> ''Q. lawsoni'' possessed well-developed pedal (foot) [[ungual]]s, which supported moderately curved claws, shorter and slightly straighter than those of tapejarids.<ref name="padian2021" />