Quetzalcoatlus

Discovery and naming , 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'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. 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 bone while investigating an arroyo on the western edge of the park, and returned to Austin with a 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. 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 in wingspan. 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". 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. Though not specified in the original publication, Lawson named the genus after the Aztec feathered serpent god Quetzalcōātl, while the specific name honors John Knudsen Northrop, the founder of Northrop Corporation, who drove the development of large tailless Northrop YB-49 aircraft designs resembling Quetzalcoatlus. 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. 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. 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, the 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. 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. Kevin Padian was the primary organizer of the project. though some authors argued the second publication referencing the initial description was sufficient. The species received a diagnosis in a 1991 paper by Lev Nessov, but no action was taken to formalize the name. 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 Romanian azhdarchid Hatzegopteryx. 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. The name-bearing type specimen of Q. northropi is 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 assigned 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. Other assigned and reclassified material Though most pterosaur remains from Big Bend have been assigned to Quetzalcoatlus, some other material exists. Most prominent amongst these is a specimen discovered around 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. 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. it was considered an indeterminate azhdarchid or a specimen of Montanazhdarcho by subsequent studies. A neck vertebra from the Hell Creek Formation, also from Montana but dating to the Maastrichtian, was discovered in 2002 and initially assigned in 2006 to Quetzalcoatlus. The 2021 paper merely considered it an azhdarchiform specimen of uncertain affinities, but the 2025 study named it as the holotype of a distinct genus Infernodrakon. Another neck vertebra, discovered in the similarly aged Lance Formation in Wyoming and first described in 1964, was later assigned to Quetzalcoatlus by Brent H. Breithaupt in 1982; later studies assigned it to Azhdarcho or an indeterminate azhdarchid or azhdarchiform. ==Description==

of Q. northropi Quetzalcoatlus northropi was among the largest azhdarchids, though was rivalled in size by Arambourgiania and Hatzegopteryx and Wellnhopterus), and long-necked taxa with longer, slenderer beaks (i.e. Zhejiangopterus). Quetzalcoatlus falls squarely into the latter category. Based on the limb morphology of 'Q.' lawsoni, related azhdarchids such as Zhejiangopterus, and pterosaurs at large, in addition to azhdarchid tracks from South Korea, Quetzalcoatlus was likely quadrupedal. Size Quetzalcoatlus is regarded as one of the largest pterosaurs, Other estimates contemporary to Bakker's, however, consistently supported a smaller size of . the head may have been held at a height of more than , similar to that of an extant giraffe. Crawford Greenewalt gave mass estimates of between for Q. northropi, with the former figure assuming a small wingspan of , and the latter assuming a far larger wingspan of . Gregory S. Paul estimated higher body masses of kg for Q. lawsoni specimen TMM 41691-1 in 2002, 'Quetzalcoatlus' lawsoni Much of what has been said regarding Quetzalcoatlus northropi was informed from the now-separate species Q. lawsoni. Henry Thomas and Skye N. McDavid, in 2025, performed a revision of Azhdarchomorpha which recovered Quetzalcoatlus as polyphyletic, with Q. lawsoni not clading with the type species Q. northropi. 'Quetzalcoatlus' lawsoni and other azhdarchids had unusually thick jugals among pterosaurs, which may have strengthened the skull in a way that enabled the beak's use in agonistic (fighting) behaviors; while this was most applicable to more robust-skulled genera such as Hatzegopteryx, Darren Naish and Mark Witton suggested in 2013 that this may have been true of most, if not all azhdarchids. Like in other azhdarchoids, the cervical vertebrae were low, with neural arches that were essentially inside the centrum. While airborne, the neck of Q. northropi would have likely assumed a slight S-shaped curve, similar to swans. The vertebrae at the base of the neck and the pectoral (shoulder) girdle are poorly known. The first four dorsal (back) vertebrae are fused into a notarium, and particularly ornithocheiroids. 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 caudal (tail) vertebrae are preserved in any Quetzalcoatlus specimens. Quetzalcoatlus lawsoni (presumably Quetzalcoatlus northropi) 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. They were plantigrade, meaning that they walked with the sole of the foot flat on the ground. Q. lawsoni possessed well-developed pedal (foot) unguals, which supported moderately curved claws, shorter and slightly straighter than those of tapejarids. ==Classification==

holotype (on the right)|leftWhen describing Quetzalcoatlus in 1975, Douglas Lawson and Crawford Greenewalt opted not to assign it to a clade more specific than Pterodactyloidea, Unaware of that subfamily, in the same year, Kevin Padian erected the family Titanopterygiidae to accommodate Quetzalcoatlus and Titanopteryx, defining it based on the length and general morphology of the cervical vertebrae. Two years later, in 1986, noting commonalities not only in contained genera but in diagnostic features, he rendered Titanopterygiidae a junior synonym of Azhdarchinae, elevating the latter to family level and forming the family Azhdarchidae. In 2003, the clade Azhdarchoidea was defined by David Unwin. Azhdarchids were determined to form a clade, Neoazhdarchia, with Tapejaridae. Montanazhdarcho from North America and Zhejiangopterus from China were incorporated into Azhdarchidae. In the supplementary material for their 2014 paper describing Kryptodrakon progenitor, Andres, James Clark and Xing Xu named a new subfamily, Quetzalcoatlinae, of which Quetzalcoatlus'' is the type genus. The relationship between Quetzalcoatlus and other giant azhdarchids, like Arambourgiania and Hatzegopteryx, is not certain. In 2021, Brian Andres recovered them as sister taxa, with Arambourgiania being the sister taxon of Quetzalcoatlus and Hatzegopteryx being slightly more basal. A similar dichotomy was recovered by Leonardo Ortiz David and colleagues that same year, with the inclusion of Thanatosdrakon as Quetzalcoatlus sister genus. The first of the below cladograms shows the results recovered by Andres in 2021, and the second shows the results recovered by Ortiz David and colleagues in 2022. Topology 1: Andres (2021). Topology 2: Ortiz David and colleagues (2022). }} }} }}|style=font-size:90%; line-height:90%;|label1=Azhdarchidae}} A 2025 analysis by Henry N. Thomas and Skye N. McDavid performed a revision of Azhdarchomorpha which recovered Quetzalcoatlus as polyphyletic, with the type species Q. northropi being sister to Thanatosdrakon while Q. lawsoni claded in a polytomy with the 'Tous pterosaur' and other unnamed specimens that was recovered as sister to Thanatosdrakon and Q. northropi. A reproduction of their results is below: }} == Paleobiology ==

Terrestrial locomotion ''. Azhdarchids are the only group of pterosaurs to which trackways have been confidently assigned. Haenamichnus, from South Korea, matches azhdarchids in foot shape, age, and size; it is estimated that most trackmakers had a wingspan of about , One long Haenamichnus trackway shows that azhdarchids walked with their limbs held directly underneath their body, The model was based on a then-current weight estimate of around , far lower than more modern estimates of over . The method of flight in these pterosaurs depends largely on their weight, which has been controversial, and widely differing masses have been favored by different scientists. Some researchers have suggested that these animals employed slow, soaring flight, while others have concluded that their flight was fast and dynamic. Henderson's work was also further criticized by Witton and Habib in another study, which pointed out that, although Henderson used excellent mass estimations, they were based on outdated pterosaur models, which caused his mass estimations to be more than double what Habib used in his estimations and that anatomical study of Q. northropi and other big pterosaur forelimbs showed a higher degree of robustness than would be expected if they were purely terrestrial. Studies of Q. northropi and Q. lawsoni published in 2021 by Kevin Padian and colleagues instead suggested that Quetzalcoatlus was a very powerful flier. While Padian himself also suggested that the legs and feet were likely tucked under the body during flight as in modern birds, co-authors John Conway and James Cunningham endorsed a system more in line with conventional models of pterosaur flight, wherein the hind limbs were splayed out while the animal was airborne. In 2008, Michael Habib suggested that the only feasible takeoff method for a Quetzalcoatlus was one that was mainly powered by the forelimbs. In 2010, Mark Witton and Habib noted that the femur of Quetzalcoatlus was only a third as strong as what would be expected from a bird of equal size, whereas the humerus is considerably stronger, and affirmed that an azhdarchid the size of Quetzalcoatlus would have great difficulty taking off bipedally. Thus, they considered a quadrupedal launching method, with the forelimbs applying most of the necessary force, a likelier method of takeoff. ==Paleoecology==

and Tyrannosaurus, giant dinosaurs characteristic of the fauna Quetzalcoatlus'' inhabited Definitive fossils of Quetzalcoatlus have only been found from the Javelina Formation of Texas, though similar and potentially congeneric azhdarchids are known from isolated bones across North America. The formation consists of around of fluvial deposits from the middle to late Maastrichtian, and is gradually overlain by Black Peaks Formation which contains the Cretaceous–Paleogene boundary. At the time of sedimentation, the coastline of the seaway was around southeast of the formation. Specimens of Quetzalcoatlus are only known from the upper half of the formation where they are the most common vertebrate, with magnetostratigraphy and uranium–lead dating demonstrating that these deposits were from the latest Maastrichtian around 67 to 66 million years ago. Additional pterosaur specimens that may be Quetzalcoatlus are found in older parts of the formation, though the single oldest pterosaur fossil belongs to the azhdarchid Wellnhopterus. As Q. lawsoni is known only from the upper part of the formation, and those of Q. northropi are from the top of the Javelina or the base of the Black Peaks Formations, it is possible that the three taxa succeeded each other, though uncertainty allows for some overlap of the species of Quetzalcoatlus. Even if Q. lawsoni and Q. northropi coexisted, their remains are found in different facies so they may have lived in different habitats. Specimens of Q. northropi are found in stream-channel deposits consisting of sandstone and conglomerate, where scattered skeletons, limb bones of Alamosaurus, and local log jams are also found. In places, the conglomerates contain accumulations of small bones such as vertebrae, scales, teeth, and osteoderms of gar, fish, turtles, and crocodilians, and shells of gastropods. The flow in these streams fluctuated dramatically and was possibly ephemeral with short duration flooding events. While abandoned channel-lake deposits are the least common in the formation, most specimens of Q. lawsoni have been found in them. As the channels were abandoned or cut off from active flow, the lakes would develop where sediments would accumulate and occasionally be flooded by nearby streams. Burrows can be found throughout these deposits, bones are normally excrusted with calcite, and the carbonates present suggest photosynthetic algae and microbes as found in alkaline lakes. The lakes were several hundred meters wide but only a few meters deep at their maximum extent, though the main fossil layer is from a single prolonged lake development. which suggests that they were terrestrial generalists which fed upon small terrestrial prey, especially small tetrapods. Paul suggested that Q. northropi was analogous to modern storks, specializing in plucking small vertebrates, such as frogs and turtles, from around watercourses. This initial iteration was supported by Sankar Chatterjee and R. J. Templin, who believed that many pterodactyloids adopted such a lifestyle. and by S. Christopher Bennett in 2001. In a 2008 paper on the paleoecology of azhdarchids, Mark Witton and Darren Naish reviewed previous models of their ecology and found the majority to be untenable. The anatomy possessed by azhdarchids was, to them, indicative of terrestrial prey capture. They argued that the family were ecologically closest to storks or ground hornbills, and coined the term "terrestrial stalker" to collectively describe them. Pterosaurs were generally thought to have gone gradually extinct by decreasing in diversity towards the end of the Cretaceous, but Longrich and colleagues suggested this impression could be a result of the poor fossil records for pterosaurs (the Signor-Lipps Effect). Pterosaurs during this time had increased niche-partitioning compared to earlier faunas from the Santonian and Campanian ages, and they were able to outcompete birds in large size based niches, and birds therefore remained small, not exceeding wingspans during the Late Cretaceous (most pterosaurs during this time had larger wingspans, and thereby avoided the small-size niche). To these researchers, this indicated that the extinction of pterosaurs was abrupt instead of gradual, caused by the catastrophic Chicxulub impact. Their extinction freed up more niches that were then filled by birds, which led to their evolutionary radiation in the Early Cenozoic. Smaller theropods including the dromaeosaurid Saurornitholestes and an indeterminate troodontid have been found, as well as a variety of fishes, smaller reptiles, and mammals. Most fishes, smaller reptiles and mammals were found through the screening of microfossil localities, which also discovered scraps of dinosaurs. Fish include the stingray Dasyatis, the bowfin, the gar Atractosteus, while amphibians include an indeterminate frog, and reptiles are represented by the lizard Glyptosaurus, the snake Dunnophis, and the crocodile Brachychampsa. Mammals are very common in microfossil sites of both the Black Peaks and Javelina Formations, represented in the latter by the multituberculates Ptilodus, Mesodma, Stygimys, and Viridomys, indeterminate therians, and the metatherians Peratherium, Gelastops, Bryanictis, Mixodectes, Palaechthon, Eoconodon, Carsioptychus, Haploconus, Ellipsodon, and Promioclaenus. ==Cultural significance==

In 1975, artist Giovanni Caselli depicted Quetzalcoatlus as a small-headed scavenger with an extremely long neck in the book The evolution and ecology of the Dinosaurs by British paleontologist Beverly Halstead. Over the next twenty-five years prior to future discoveries, it would launch similar depictions colloquially known as "paleomemes" in various books, as noted by Darren Naish. In 1985, the US Defense Advanced Research Projects Agency (DARPA) and AeroVironment used Q. northropi as the basis for an experimental ornithopter unmanned aerial vehicle (UAV). They produced a half-scale model weighing , with a wingspan of . Coincidentally, Douglas A. Lawson, who discovered Q. northropi in Texas in 1971, named it after John "Jack" Northrop, a developer of tailless flying wing aircraft in the 1940s. The replica of Q. northropi incorporates a "flight control system/autopilot which processes pilot commands and sensor inputs, implements several feedback loops, and delivers command signals to its various servo-actuators". It is on exhibit at the National Air and Space Museum. In 2010, several life-sized models of Q. northropi were put on display on London's South Bank as the centerpiece exhibit for the Royal Society's 350th-anniversary exhibition. The models, which included both flying and standing individuals with wingspans of over , were intended to help build public interest in science. The models were created by scientists from the University of Portsmouth. ==See also==