Editing Quetzalcoatlus (section)

==Research history and taxonomy==
===Discovery and naming===
[[File:Big_Bend_Chihuahuan_Desert.jpg|thumb|left|The known fossils of ''Quetzalcoatlus'' were discovered in [[Big Bend National Park]], [[Texas]]]]
The genus ''Quetzalcoatlus'' is based on fossils discovered in rocks pertaining to the Late Cretaceous [[Javelina Formation]] in [[Big Bend National Park]], [[Texas]]. Remains of dinosaurs and other prehistoric life had been found in the area since the beginning of the 20th century. The first ''Quetzalcoatlus'' fossils were discovered in 1971 by the graduate student [[Douglas A. Lawson]] while conducting field work for his [[Master of Science|Master's degree]] project on the [[paleoecology]] of the Javelina Formation. This field work was supervised by [[Wann Langston Jr.]], an experienced [[paleontologist]] who had been doing field work in the region since 1938 and since 1963 led expeditions through his position as [[curator]] at the [[Texas Science and Natural History Museum]].{{efn|At that time known as the Texas Memorial Museum}}<ref>{{cite web |title=History of the Museum |url=https://sciencemuseum.utexas.edu/about/history |publisher=The University of Texas at Austin |access-date=September 21, 2023}}</ref> The two had first visited the park together in March 1970, with Lawson discovering the first ''Tyrannosaurus rex'' fossil from Texas. Returning in 1971, Lawson discovered a {{cvt|3|ft}} bone while investigating an [[Arroyo (watercourse)|arroyo]] on the western edge of the park, and returned to [[Austin, Texas|Austin]] with a {{cvt|1|ft}} section of it. He and Langston then identified it as a [[pterosaur]] fossil based on its hollow internal structure with thin walls. Returning in November 1971 for further excavations, they were struck by the unprecedented size of the remains compared to known pterosaurs.<ref name=brown2021>{{cite journal | title=The discovery, local distribution, and curation of the giant azhdarchid pterosaurs from Big Bend National Park | last1=Brown | first1=Matthew A. | last2=Sagebiel | first2=J. Chris | last3=Andres | first3=Brian | journal=Journal of Vertebrate Paleontology | year=2021 | volume=41 | issue=sup1 | pages=2–20 | doi=10.1080/02724634.2020.1780599| doi-access=free | bibcode=2021JVPal..41S...2B }}</ref> The initial material consisted of a giant radius and ulna, two fused wristbones known as syncarpals, and the end of the wing finger. Altogether, the material comprised a partial left wing from an individual (specimen number TMM 41450-3) later estimated at over {{cvt|10|m}} in [[wingspan]].<ref name=brown2021/><ref name="andres2021">{{cite journal |last1=Andres |first1=B. |last2=Langston |first2=W. Jr. |year=2021 |title=Morphology and taxonomy of ''Quetzalcoatlus'' Lawson 1975 (Pterodactyloidea: Azhdarchoidea) |journal=Journal of Vertebrate Paleontology |volume=41 |issue=sup1 |pages=46–202 |bibcode=2021JVPal..41S..46A |doi=10.1080/02724634.2021.1907587 |issn=0272-4634 |s2cid=245125409 |doi-access=free}}</ref> Lawson described the remains in his 1972 thesis as "[[Pteranodon]] gigas", and diagnosed it as being "nearly twice as large as any previously described species of ''Pteranodon''".<ref>{{Cite book |last=Lawson |first=Douglas Allan |author-link=Douglas A. Lawson |url=https://books.google.com/books?id=fuzmtgAACAAJ |title=Paleoecology of the Tornillo Formation, Big Bend National Park, Brewster County, Texas |date=1972 |publisher=University of Texas at Austin. |language=en}}</ref><ref name=andres2021/> As a thesis is not recognized as a published worked by the [[International Code for Zoological Nomenclature]] (ICZN), "Pteranodon gigas" is not a [[Valid name (zoology)|valid name]].<ref name=andres2021/> Further field work at the site was conducted in March 1973, when fragments were found alongside a long and delicate bone connected to an apparently larger element. This fossil was left in the ground until April 1974, when they fully excavated the larger element, a humerus. Due to the close association of discovered remains, Langston felt confident there were nothing more to be found at the site. Several later excavations of the site have indeed been unsuccessful.<ref name=brown2021/>
[[File:YB49-2_300.jpg|thumb|The name of ''Q. northropi'' refers to its similar appearance to aircraft designed by [[Jack Northrop|John Knudsen Northrop]]]]
Lawson announced his discovery in the journal ''[[Science (journal)|Science]]'' in March 1975, with a depiction of the animal's size compared to a large aircraft and a ''Pteranodon'' gracing the cover of the issue. Lawson wrote that it was "without doubt the largest flying animal presently known". He illustrated and  briefly described the remains known at the time, but did not offer a name and indicated that a more extensive description was in preparation that would diagnose the species.<ref name=brown2021/><ref name="lawson1975">{{cite journal |last1=Lawson |first1=Douglas A. |year=1975 |title=Pterosaur from the Latest Cretaceous of West Texas: Discovery of the largest flying creature |department=Reports |journal=Science |volume=187 |issue=4180 |pages=947–948 |bibcode=1975Sci...187..947L |doi=10.1126/science.187.4180.947 |pmid=17745279 |s2cid=46396417}}</ref> In May, he submitted a short response to his original paper to the journal, considering how such an enormous animal could have flown. Within the paper, he briefly established the name ''Quetzalcoatlus northropi'', but did still not provide a diagnosis or a more detailed description, which would later cause nomenclatural problems.<ref name=andres2021/><ref name="lawson1975b">{{cite journal | url=https://www.science.org/doi/abs/10.1126/science.188.4189.676.b | title=Response: Could Pterosaurs Fly? | author=Lawson, Douglas A. | journal=Science | year=1975 | volume=188 | issue=4189 | pages=676–678 | doi=10.1126/science.188.4189.676.b}}</ref> Though not specified in the original publication, Lawson's named the genus after the [[Aztecs|Aztec]] feathered serpent god [[Quetzalcoatl|Quetzalcōātl]], while the [[specific name (zoology)|specific name]] honors [[Jack Northrop|John Knudsen Northrop]], the founder of [[Northrop Corporation]], who drove the development of large tailless [[Northrop YB-49]] aircraft designs resembling ''Quetzalcoatlus''.<ref name="andres2021"/> The discovery of the giant pterosaur left a strong impression on both the scientific community and the general public, and was reported on throughout the world.<ref name=andres2021/> It was featured in [[Time Magazine]] and appeared on the cover of [[Scientific American]] in 1981 alongside an article on pterosaurs by Langston.<ref name=brown2021/> The species would become referenced by over 500 scientific publications, with ''Quetzalcoatlus northropi'' becoming the single most cited pterosaur species and ''Quetzalcoatlus'' the fourth most cited pterosaur genus after ''Pteranodon'', ''[[Rhamphorhynchus]]'', and ''[[Pterodactylus]]'', much older genera with many more species than ''Quetzalcoatlus''.<ref name=andres2021/>
[[File:Pterosaur_Texas_Science_and_Natural_History_Museum_Austin_2024.jpg|thumb|left|Skeleton reconstruction of ''Quetzalcoatlus'' at the [[Texas Science and Natural History Museum]], originally mounted by Langston in the 1980s]]
Prior to the announcement of the discovery, Langston had returned to Big Bend with a group of fossil preparators in February 1973, primarily aiming to excavate bones of the dinosaur ''[[Alamosaurus]]''. One of the preparators, a young man named Bill Amaral who went on to be a respected field worker, had been skipping his lunches to conduct additional explorations of the area.<ref name=brown2021/> He came across some additional fragments of pterosaur bone on a different portion of the ridge, around 50 kilometers away from the original site.<ref name=brown2021/><ref name=andres2021/> Two more new sites quickly followed nearby, producing many fragments which the crew figured could be fit back together, in addition to a complete carpal and intact wing bone. Langston noted in his field notes that none of these bones suggested animals as large as Lawson's original specimen. Further remains came from Amaral's first site in April 1974, after Lawson's site had been exhausted; a long neck vertebra and a pair of jawbones appeared. Associated structures were initially hoped to represent filamentous [[pycnofibres]], but were later confirmed to be conifer needles. Near the end of the 1974 season, Langston stumbled over a much more complete pterosaur skeleton; it consisted of a wing, multiple vertebrae, a femur and multiple other long bones. They lacked time to fully excavate it, leaving it in the ground until the next field season. This area, where many smaller specimens began to emerge, came to be known as Pterodactyl Ridge.<ref name=brown2021/> Two of the smaller individuals were reported in the first 1975 paper by Lawson, presumed to belong to the same species, though Langston would begin to question the idea they belonged to ''Q. northropi'' by the early 1980s.<ref name=andres2021/><ref name="lawson1975"/> Excavations continued in 1976, and eight new specimens emerged in 1977; in 1979, despite complications due to losing the field notes form 1977, Langston discovered another new site that would produce an additional ten specimens. Most importantly, a humerus of the smaller animal was finally found, which Langston considered of great importance to understanding ''Quetzalcoatlus''. Several further new localities followed in 1980, but 1981 proved less successful and Langston began to suspect the ridge may have been mostly depleted of pterosaur fossils. There was similarly little success in 1982, and visits during 1983 and 1985 proved to provide the last substantive discoveries of ''Quetzalcoatlus'' fossils. Langston returned in 1989, 1991, 1992, and 1996, but only found isolated bones and fragments. Eventually a handful of additional specimens were discovered by former student Thomas Lehman. A visit to Lawson's initial site during 1991 showed that all traces of excavation had by now eroded away. Langston would visit Big Bend for the last time in 1999, having concluded the pterosaur expeditions to focus on the excavation of two skulls of ''[[Deinosuchus]]'', another famous fossil of the area.<ref name=brown2021/>

===Later research===
[[Image:Life restoration of a group of giant azhdarchids, Quetzalcoatlus northropi, foraging on a Cretaceous fern prairie.png|thumb|330px|left|A 2008 [[Mark Witton]] depiction of ''Q. northropi'' illustrating his then-novel terrestrial stalker hypothesis. Though this theory gained wide acceptance, the anatomy depicted is now considered outdated in some respects.<ref>{{Cite book |last=Witton |first=Mark P. |title=The Palaeoartist's Handbook: recreating prehistoric animals in art |date=2018 |publisher=The Crowood press Ltd |isbn=978-1-78500-461-2 |location=Ramsbury, Marlborough}}</ref>]]
The expected further description implicated by Lawson never came. For the next 50 years, the material would remain under incomplete study, and few concrete anatomical details were documented within the literature. Much confusion surrounded the smaller individuals from Pterodactyl Ridge. In a 1981 article on pterosaurs, Langston expressed reservations whether they were truly the same species as the immense ''Q. northropi''.<ref name=":3">{{Cite journal |last=Jr |first=Wann Langston |date=February 1, 1981 |title=Pterosaurs |url=https://www.scientificamerican.com/article/pterosaurs/ |access-date=January 25, 2025 |journal=Scientific American |volume=244 |issue=2 |pages=122–136 |language=en |doi=10.1038/scientificamerican0281-122|bibcode=1981SciAm.244b.122L }}</ref> In the meantime, Langston focused on the animal's publicity. He worked on a life-sized gliding replica of ''Quetzalcoatlus northropi'' with aeronautical engineer [[Paul MacCready]] between 1981 and 1985, promoting it in a dedicated IMAX film. The model was created to understand the flight of the animal — prior to Lawson's discovery such a large flier wasn't thought possible, and the subject remained controversial at the time. Furthermore, the model was intended to allow people to experience the animal in a more dynamic manner than a mere static display or film.<ref>Langston, W., Pausé, P. H., & Spears, R. G. (1986). Rebuilding the world's biggest flying creature: the second coming of Quetzalcoatlus northropi. Geology of the Big Bend Area and Solitario Dome, 125-28.</ref><ref name=bell2013/><ref name="maccready1985"/> Around this time he also created a skeletal mount of the genus that was exhibited at the Texas Memorial Museum.<ref name=bell2013>{{cite journal | url=https://www.cambridge.org/core/journals/earth-and-environmental-science-transactions-of-royal-society-of-edinburgh/article/wann-langston-jr-a-life-amongst-bones/5838704B9E717EB6B8E05A39BAC68F73 | title=Wann Langston, Jr. – a life amongst bones | journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh | last1=Bell | first1=Christopher J. | last2=Brown | first2=Matthew A. | last3=Dawson | first3=Mary R. | last4=Lundelius Jr. | first4=Ernest L. | year=2013 | volume=103 | issue=3–4 | pages=189–204 | doi=10.1017/S1755691013000443}}</ref>

The next scientific effort of note was a 1996 paper by Langston and pterosaur specialist [[Alexander Kellner]]. By this time, Langston was confident the smaller animals were a separate species. A full publication establishing such a species was still in preparation at the time, but due to the importance of the skull material for the understanding of [[azhdarchid]] anatomy, the skull anatomy was published first. In this publication, he animal was referred to as ''Quetzalcoatlus'' sp., a placeholder designation for material not assigned to any particularly valid species. Once again, the planned further publication failed to materialize for decades, and ''Quetzalcoatlus'' sp. remained in limbo.<ref name=andres2021/><ref name="kellner&langston1996">{{cite journal |last1=Kellner |first1=Alexander W. A. |last2=Langston |first2=Wann Jr. |year=1996 |title=Cranial remains of ''Quetzalcoatlus'' (Pterosauria, Azhdarchidae) from Late Cretaceous sediments of Big Bend National Park, Texas |journal=Journal of Vertebrate Paleontology |volume=16 |issue=2 |pages=222–231 |bibcode=1996JVPal..16..222K |doi=10.1080/02724634.1996.10011310}}</ref> A publication on the bioaeromechanics of the genus was also planned by Langston and James Cunningham, but this failed to materialize and the partially completed manuscript later became lost.<ref name=padian2021/> Ultimately, a comprehensive publication on ''Quetzalcoatlus'' sp. would not appear before Langston's death in 2013. By this point he had produced many notes and individual descriptions, but had not begun writing any formal manuscript that could be published.<ref name=andres2021/>
[[File:Quetzalcoatlus lawsoni.png|thumb|Life reconstruction of ''Q. lawsoni''.]]
In 2021, a comprehensive description of the genus was finally published, the 19th entry in the Memoir series of special publications by the [[Society of Vertebrate Paleontology]] in the ''[[Journal of Vertebrate Paleontology]]''. It consisted of five studies published together.<ref name=preface>{{cite journal | title=Preface | journal=Journal of Vertebrate Paleontology | year=2021 | volume=41 | issue=sup1 | pages=1 | doi=10.1080/02724634.2020.1853560 | last1=Brown | first1=Matthew A. | last2=Padian | first2=Kevin | bibcode=2021JVPal..41S...1B | doi-access=free }}</ref> Kevin Padian was the primary organizer of the project.<ref name=andres2021/> A paper on the history of discoveries in Big Bend National Park was authored by Matthew J. Brown, Chris Sagebiel, and Brian Andres. It focused on curating a comprehensive list of specimens belonging to each species to ''Quetzalcoatlus'' and the locality information of each within Big Bend.<ref name=brown2021/> Thomas Lehman contributed a study on the paleonvironment that ''Quetzalcoatlus'' would have resided within, based upon work he had begun with Langston as early as 1993.<ref name="lehman2021" /> Brian Andres published a study on the morphology and taxonomy of the genus, established the species ''Quetzalcoatlus lawsoni'' for the smaller animal that had gone for decades without a name. The specific name honoured Lawson, who discovered ''Quetzalcoatlus''. Despite not contributing directly to the written manuscript, the authors of the memoir and Langston's family agreed that he posthumously be considered a co-author due the basis of the work in the decades of research he dedicates to the subject.<ref name=andres2021/> Also authored by Andres was a phylogenetic study of ''Quetzacoatlus'' and its relationships within Pterosauria, with a focus on the persistence of many lineages into the [[Late Cretaceous]] contra classical interpretations of ''Quetzalcoatlus'' as the last of a dying lineage.<ref name="Andres-2021"/> Finally, a study on the functional morphology of the genus was authored by Padian, James Cunningham, and [[John Conway (palaeoartist)|John Conway]] (who contributed scientific illustrations and cover art to the Memoir<ref name=andres2021/>), with Langston once again considered a posthumous co-author due to his foundational work on the subject.<ref name="padian2021"/> Brown and Padian prefaced the Memoir, who once again emphasized their gratitude to Langston for his decades of work on the animal leading up to the publication.<ref name=preface/>

===Taxonomy and material===
[[File:Cast of Quetzalcoatlus northropi humerus 01 - Pterosaurs Flight in the Age of Dinosaurs.jpg|thumb|upright|left|Cast of the [[humerus]] from the [[holotype]] of ''Q. northropi'']]
The genus ''Quetzalcoatlus'' consists of two valid species: the [[type species]] ''Q. northropi'' and the second species ''Q. lawsoni''. Though the name was introduced in 1975, the lack of a formal description complicated its validity for several decades. The oldest name for the species is "''Pteranodon'' gigas", from Lawson's 1973 thesis. However, the [[International Code of Zoological Nomenclature]] (ICZN) does not consider a thesis to be a formal publication capable of establishing of a taxon, and the name has not been used since. Regarding the genus ''Quetzalcoatlus'' and species ''Q. northropi'', the name being established in a separate publication than the anatomical diagnosis also failed ICZN standards.<ref name=andres2021/> As such, it was argued that the name was a ''[[nomen nudum]]'', an intended but invalid scientific name,<ref name=andres2021/><ref name=Navajodactylus>{{cite journal |author=Robert M. Sullivan |author2=Denver W. Fowler |name-list-style=amp |year=2011 |title=''Navajodactylus boerei'', n. gen., n. sp., (Pterosauria, ?Azhdarchidae) from the Upper Cretaceous Kirtland Formation (upper Campanian) of New Mexico |url=http://www.robertmsullivanphd.com/uploads/167._Sullivan_and_Fowler__Navajodactylus__COLOR.pdf |journal=Fossil Record 3. New Mexico Museum of Natural History and Science, Bulletin |volume=53 |pages=393–404 }}</ref> though some authors argued the second publication referencing the initial description was sufficient.<ref name="averianov2014">{{cite journal | title=Review of taxonomy, geographic distribution, and paleoenvironments of Azhdarchidae (Pterosauria) | author=Averianov, Alexander | journal=ZooKeys | year=2014 | issue=432 | pages=1–107 | doi=10.3897/zookeys.432.7913| doi-access=free | pmid=25152671 | pmc=4141157 | bibcode=2014ZooK..432....1A }}</ref> The species received a diagnosis in a 1991 paper by Lev Nessov, but no action was taken to formalize the name.<ref name=andres2021/><ref>Nessov, L. A. (1991). Gigantskiye letayushchiye yashchery semeystva Azhdarchidae. I. Morfologiya, sistematika. Vestnik Leningradskogo Universiteta. Seriya, 7, 14-23.</ref> Furthermore, a study by [[Mark Witton]] and colleagues in 2010 doubted whether ''Quetzalcoatlus'' could be validly diagnosed at all. They noted that the bones preserved in the holotype of ''Q. northropi'' were not typically considered to be taxonomically informative between close relatives, and that they appeared extremely similar to those of other giant azhdarchids such as the [[Romania]]n azhdarchid ''[[Hatzegopteryx]]''.<ref name="witton2010">{{cite journal|last1=Witton|first1=M.P.|last2=Martill|first2=D.M.|last3=Loveridge|first3=R.F.|year=2010|title=Clipping the wings of giant pterosaurs: comments on wingspan estimations and diversity|journal=Acta Geoscientica Sinica|volume=31|pages=79–81|url=https://www.researchgate.net/publication/287830761}}</ref> Both of these issues were settled in the 2021 paper, whose rediagnosis affirmed ''Quetzalcoatlus'' as distinct. The authors agreed that the original paper did not constitute a valid establishment of the name. The authors noted their publication could serve as the a basis for the name, but did not wish to change the previously presumed authorship of the name. Thus, they submitted an application for the ICZN in 2017 to make an exception to the requirements, and had Lawson's second 1975 paper to be declared as the valid authority of the genus and species. The approval of this ICZN petition on August 30, 2019, conserved and formalized the binomen ''Quetzalcoatlus northropi'' as the type species.<ref name=andres2021/><ref name=ICZN>{{cite journal | url=https://bioone.org/journals/the-bulletin-of-zoological-nomenclature/volume-74/issue-1/bzn.v74.a010/Case-3728--Quetzalcoatlus-northropi-Reptilia-Pterosauria--proposed-availability/10.21805/bzn.v74.a010.short | title=Case 3728 — Quetzalcoatlus northropi (Reptilia, Pterosauria): proposed availability and attribution of authorship to lawson, 1975 | journal=The Bulletin of Zoological Nomenclature | last1=Andres | first1=Brian | last2=Padian | first2=Kevin | last3=Rowe | first3=Timothy B. | last4=Bell | first4=Christopher J. | last5=Brown | first5=Matthrew A. | last6=Sagebiel | first6=J. Chris | last7=Lehman | first7=Thomas M. | last8=Cunningham | first8=James R. | year=2017 | volume=74 | issue=1 | pages=34–37 | doi=10.21805/bzn.v74.a010}}</ref><ref>{{cite journal|title=Opinion 2440 (Case 3728) – Quetzalcoatlus northropi Lawson, 1975 (Reptilia, Pterosauria): generic and specific names ruled available with the indicated authorship|journal=The Bulletin of Zoological Nomenclature|volume=76|issue=1|pages=155–156|doi=10.21805/bzn.v76.a047|date=August 2019}}</ref>
[[File:Quetzaloatlus_lawsoni_skeletal_reconstruction.jpg|thumb|Skeletal reconstruction showing known material of ''Q. lawsoni'']]
Though Lawson originally considered all ''Quetzalcoatlus'' remains to belong to one species, today two species are recognized: the large ''Quetzalcoatlus northropi'' and the smaller ''Quetzalcoatlus lawsoni''. The exact nature of what material belongs to each species remains unclear, due in part to the distribution of specimens across various localities and stratigraphic levels found at Big Bend, as well as the limited scope of ''Q. northropi'' material to compare to. The name-bearing [[type specimen]] of ''Q. northropi'' is [[Texas Science and Natural History Museum|TMM]] 41450-3, a partial wing. It includes a humerus, radius, ulna, wrist bones, finger bones, and many elements of the elongate wing finger, in addition to thousands of unidentifiable fragments. It is from the uppermost rocks of the Javelina Formation, making it one of the youngest pterosaur specimens known. Only a single other specimen can confidently be referred to the same species, a left ulna designated TMM 44036-1 known from the [[Black Peaks Formation]], around three quarters the size of the type specimen and sharing distinctive anatomy. Four other specimens share a similarly giant size, but cannot be definitively assigned to ''Q. northropi'' in lack of overlapping material or distinguishing anatomical regions. TMM 41047-1 and TMM 41398-3, are both partial femurs, the former twice the size of that seen in ''Q. lawsoni''. Their anatomy indicates they belonged to the same species, and is distinct from that of ''Q. lawsoni''. Part of a wing finger, TMM 41398-4, is also of the correct size to belong to ''Q. northropi'' but does not preserve the essential anatomy to confirm its identity. This specimen and the smaller femur were the first two specimens Lawson discovered, prior to uncovering the type specimen. Finally, one of the oldest pterosaur specimens in Big Bend is a giant cervical vertebra not matching that of smaller species from the formation. Whilst conventional pterosaur research would assign all of these to ''Q. northropi'', the 2021 redescription preferred to be cautious and merely assigned them to ''Q. cf. northropi'', indicating uncertainty.<ref name=andres2021/>

The assignment of remains to ''Q. lawsoni'' has proved more simplistic; a large quantity of similar remains were found together in nearby sites, 50&nbsp;km from the ''Q. northropi'' locality. In total, 305 different fossil elements from 214 specimens are known, all of which are considered consistent with assignment to the same species. This is the most amount of remains referred to any singular species of pterosaur. The vast majority of the dozens of specimens are disarticulated individual bones. A few individual animals are, however, represented by associated remains; identification of these individuals was complicated by each bone being catalogued under a separate number, which was revised as part of the 2021 study. The most complete specimen is TMM 41961-1, which possesses the most complete skull as well as several neck vertebrae, much of both wings, femurs, tibiotarsi, two metatarsals, and one of the toe bones. It was one of the original specimens described by Langston in 1975, and in accordance with Langston's wishes and its completeness was designated as the type specimen. Two less complete specimens, TMM 42180-14 and TMM 42161-1, were also preserved in partial articulation, the former mostly composed of limb and neck bones whilst the latter consists of neck and skull bones. Beyond this, identification of individual specimens is difficult. Two other specimens are more loosely associated, and others may have belonged to a single individual but are too weathered to identify with confidence. In some cases two or three neck vertebrae were found in presumed association, and similar loose associations of one or two limbs bones are seen in several cases. Taken together, nearly the entirely skeleton is represented, with the exception of some of the back of the skull. Eight different specimens preserve various portions of the skull, together allowing for a rather complete picture (excepting a portion of the back of the skull), and similarly the entire mandible is represented when cross-referencing four specimens. All nine neck vertebrae are known, and most torso vertebrae are known through the preservation of the notarium and synsacrum, structures consisting of several fused vertebrae in [[ornithocheiroid]] pterosaurs; it is unknown how many unfused vertebrae may have existed between these structures. Every single bone in the arm is known from at least one complete specimen, and the hindlimbs and pelvis are also more or less all present, though the femur and pelvis suffer from poor preservation.<ref name=andres2021/>

=== Other referred and reclassified material ===
[[File:Aff Quetzalcoatlus - Longrich et al 2018.PNG|left|thumb|FSAC-OB 14, a vertebra assigned to aff. ''Quetzalcoatlus'']]
Though most pterosaur remains from Big Bend have been referred to ''Quetzalcoatlus'', some other material exists. Most prominent amongst these is a specimen discovered around {{convert|380|m|ft}} north of the Pterodactyl Ridge localities, designated as TMM 42489-2 and compromising a partial skull and jaws as well as five articulated neck vertebrae. It was immediately noted for its distinct shorted-jawed anatomy compared to what had come to be expected from ''Q. lawsoni'' specimens.<ref name=brown2021/><ref name=andres2021/> Despite this distinctiveness, it was referred to as a separate ''Quetzalcoatlus sp.'' in a 1991 book by Langston. As early as 1996, however, this was revised with recognition it was certainly a new genus informally known as the "short-faced pterosaur". It was formally named in the 2021 paper alongside ''Q. lawsoni'', as the genus ''[[Wellnhopterus]]''. In addition to this specimen, several indeterminate azhdarchid remains and some remains too fragmentary to assign beyond [[Pterosauria]] are known from Big Bend. Some of these represent smaller animals than the uniformly sized ''Q. lawsoni'' remains. Whether any of these remains represented separate animals from ''Quetzalcoatlus'' cannot be determined.<ref name=andres2021/>
[[File:Cryodrakon_holotype_cervical_IV,_humerus,_pteroid,_and_tibia..jpg|thumb|Specimens of ''[[Cryodrakon]]'', once considered to represent ''Quetzalcoatlus'']]
Several specimens from across Late Cretaceous North America were historically referred to ''Quetzalcoatlus''.<ref name=thomas2025/> In 1982 a femur from the [[Campanian]] aged [[Dinosaur Park Formation]] of [[Alberta]], [[Canada]] was referred to the genus by [[Philip J. Currie]] and [[Dale Russell]].<ref name="Currie1982">{{cite journal |last1=Currie |first1=Philip J. |last2=Russell |first2=Dale A. |date=1982 |title=A giant pterosaur (Reptilia: Archosauria) from the Judith River (Oldman) Formation of Alberta |journal=Canadian Journal of Earth Sciences |volume=19 |issue=4 |pages=894–897 |bibcode=1982CaJES..19..894C |doi=10.1139/e82-074}}</ref><ref name=Currie2005>{{Cite book |last1=Currie |first1=Philip J. |author-link1=Philip J. Currie |url=https://archive.org/details/dinosaurprovinci0000unse/ |title=Dinosaur Provincial Park : a spectacular ancient ecosystem revealed |last2=Godfrey |first2=Stephen J. |date=2005 |publisher=Bloomington : Indiana University Press |isbn=978-0-253-34595-0 |editor-last=Currie |editor-first=Philip J. |chapter=Pterosaurs |editor-last2=Koppelhaus |editor-first2=Eva B.}}</ref><ref name=Hone2019>{{Cite journal |last1=Hone |first1=D. |last2=Habib |first2=M. |last3=Therrien |first3=F. |date=September 2019 |title=''Cryodrakon boreas'', gen. et sp. nov., a Late Cretaceous Canadian azhdarchid pterosaur |url=https://qmro.qmul.ac.uk/xmlui/handle/123456789/60704 |journal=Journal of Vertebrate Paleontology |volume=39 |issue=3 |pages=e1649681 |bibcode=2019JVPal..39E9681H |doi=10.1080/02724634.2019.1649681 |s2cid=203406859}}</ref> Currie later described further remains from Dinosaur Park in a 2005 book, noting their morphological similarity to ''Quetzalcoatlus'' but expressing caution against referral to the genus.<ref name=Currie2005/> In 2019, however, all azhdarchid remains from the formation were revised as distinct from ''Quetzalcoatlus'' and named as the new genus ''[[Cryodrakon]]''.<ref name=Hone2019/> A humerus from the [[Two Medicine Formation]] in [[Montana]] was also provisionally referred to the genus;<ref name=padian1992>{{cite journal | url=https://www.tandfonline.com/doi/abs/10.1080/02724634.1992.10011433 | title=New light on Late Cretaceous pterosaur material from Montana | journal=Journal of Vertebrate Paleontology | last1=Padian | first1=Kevin | last2=Smith | first2=Matt | year=1992 | volume=12 | issue=1 | pages=87–92 | doi=10.1080/02724634.1992.10011433}}</ref> it was considered an indeterminate azhdarchid or a specimen of ''[[Montanazhdarcho]]'' by subsequent studies.<ref>{{cite journal | author = Alexander Averianov | year = 2014 | title = Review of taxonomy, geographic distribution, and paleoenvironments of Azhdarchidae (Pterosauria) | doi = 10.3897/zookeys.432.7913 | journal =ZooKeys | issue = 432 | pages = 1–107 | pmid=25152671 | pmc=4141157| doi-access = free | bibcode = 2014ZooK..432....1A }}</ref><ref>{{Cite journal |last1=Starkey |first1=Rebecca |last2=Habib |first2=Michael |last3=Persons |first3=W. Scott |date=June 1, 2024 |title=A pteranodontid wing with traces of extensive invertebrate scavenging from the Pierre Shale (Sharon Springs Member, Campanian–Maastrichtian), east central Wyoming (Niobrara County) |url=https://www.sciencedirect.com/science/article/pii/S0195667124000107 |journal=Cretaceous Research |volume=158 |pages=105837 |doi=10.1016/j.cretres.2024.105837 |bibcode=2024CrRes.15805837S |issn=0195-6671}}</ref> A neck vertebra from the [[Hell Creek Formation]], also from Montana but dating to the [[Maastrichtian]], was discovered in 2002 and initially referred in 2006 to ''Quetzalcoatlus''.<ref name="henderson&peterson2006">{{cite journal|last1=Henderson|first1=Michael D.|last2=Peterson|first2=Joseph E.|title=An azhdarchid pterosaur cervical vertebra from the Hell Creek Formation (Maastrichtian) of southeastern Montana|journal=Journal of Vertebrate Paleontology|year=2006|volume=26|issue=1|pages=192–195|doi=10.1671/0272-4634(2006)26[192:AAPCVF]2.0.CO;2|s2cid=130751879|url=http://doc.rero.ch/record/15687/files/PAL_E2073.pdf}}</ref> The 2021 paper merely considered it an [[azhdarchoidea|azhdarchiform]] specimen of uncertain affinities, but the 2025 study named it as the holotype of a distinct genus ''[[Infernodrakon]]''.<ref name=andres2021/><ref name=thomas2025>{{Cite journal |last=Thomas |first=Henry N. |last2=Hone |first2=David W. E. |last3=Gomes |first3=Timothy |last4=Peterson |first4=Joseph E. |title=Infernodrakon hastacollis gen. et sp. nov., a new azhdarchid pterosaur from the Hell Creek Formation of Montana, and the pterosaur diversity of Maastrichtian North America |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2024.2442476 |journal=Journal of Vertebrate Paleontology | year=2025 |volume=0 |issue=0 |pages=e2442476 |doi=10.1080/02724634.2024.2442476 |issn=0272-4634}}</ref>

Another neck vertebra, discovered in the similarly aged [[Lance Formation]] in [[Wyoming]] and first described in 1964, was later referred to ''Quetzalcoatlus'' by Brent H. Breithaupt in 1982; later studies referred it to ''[[Azhdarcho]]'' or as an indeterminate azhdarchid or azhdarchiform.<ref name=andres2021/><ref name=Breithaupt1982>{{cite journal | url=https://pubs.geoscienceworld.org/uwyo/rmg/article-abstract/21/2/123/110696/Paleontology-and-paleoecology-of-the-Lance | title=Paleontology and paleoecology of the Lance Formation (Maastrichtian), east flank of Rock Springs Uplift, Sweetwater County, Wyoming | journal=Rocky Mountain Geology | last1=Breithaupt | first1=Brent H. | year=1982 | volume=21 | issue=2 | pages=123–151}}</ref><ref name=thomas2025/> The 2025 ''Infernodrakon'' study found it to be distinguishable from taxon, but anatomically compatible with ''Q. lawsoni''; when tested in a phylogenetic analysis, they found it to form a [[polytomy]] with ''Q. lawsoni'', ''Q. northropi'', and a Moroccan specimen. Therefore, they considered it plausible it belonged to a small ''Q. lawsoni'' individually, but decided to merely make a tentative referral to ''Quetzalcoatlus'' at the genus level due to the incomplete nature of the specimen.<ref name=thomas2025/> The Moroccan specimen, from the [[Ouled Abdoun Basin]] (Maastrichtian), is designated as [[Hassan II University of Casablanca|FSAC]]-OB 14 and was referred to aff. ''Quetzalcoatlus'' by a 2018 study. This indicates it is considered unlikely to belong to the genus but bears extreme anatomical similarity to it.<ref name="longrich2018">{{cite journal|last1=Longrich|first1=Nicholas R.|last2=Martill|first2=David M.|last3=Andres|first3=Brian|last4=Penny|first4=David|title=Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary|journal=PLOS Biology|year=2018|volume=16|issue=3|pages=e2001663|doi=10.1371/journal.pbio.2001663|pmid=29534059|pmc=5849296|doi-access=free}}</ref>