Editing Quetzalcoatlus (section)

===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/>