Quetzalcoatlus

Quetzalcoatlus (/kɛtsəlkoʊˈætləs/ ^ⓘ) is a genus of azhdarchid pterosaur that lived during the Maastrichtian age of the Late Cretaceous in North America. The type specimen, found in 1971 in the Javelina Formation of Texas, United States, is made of several wing fragments. In 1975, Douglas Lawson described it as Quetzalcoatlus northropi.

The generic name refers to Quetzalcōātl, the Aztec serpent god of the sky. The specific name honors Jack Northrop, who designed a tailless fixed-wing aircraft. Remains of a second species were found between 1972 and 1974, also by Lawson, about 40 km (25 mi) from the Q. northropi site. In 2021, Brian Andres and, after his death, Wann Langston Jr. gave these remains the name Quetzalcoatlus lawsoni. This was part of a series of publications on the genus.

Quetzalcoatlus northropi has become famous as a possible candidate for the largest flying animal ever discovered. However, estimating its size has been difficult because the only known specimen is made of fragments. Over the years, wingspan estimates have ranged from 5.2–25.8 m (17–85 ft). More recent estimates hover around 10–11 m (33–36 ft).

Early ideas about what Quetzalcoatlus ate ranged from scavenging to skimming the water like the modern skimmer bird. More recent research suggests it most likely hunted small prey on the ground, much like storks and ground hornbills. This idea is called the terrestrial stalking hypothesis, and it is thought to be a common feeding behavior among large azhdarchids. The disputed second species, Q. lawsoni, seems to have lived near alkaline lakes, and it may have eaten small water-dwelling invertebrates. Q. northropi is thought to have been fairly solitary, while Q. lawsoni appears to have been highly gregarious, or social.

Azhdarchids like Quetzalcoatlus spent much of their time on the ground compared to other pterosaurs, but even the largest could still fly. Based on work by Mark P. Witton and Michael Habib in 2010, it now seems likely that pterosaurs, especially larger taxa such as Quetzalcoatlus, took off quadrupedally, from a four-legged position. They used the powerful muscles of their front legs to push themselves off the ground and into the air.

Research history and taxonomy

The first fossils of this giant pterosaur were found in 1971 in the Javelina Formation of Big Bend National Park in Texas. The graduate student Douglas A. Lawson found them during field work for his Master's degree project on the paleoecology of the rocks, under the supervision of Wann Langston Jr., an experienced paleontologist and curator at the Texas Science and Natural History Museum. Lawson found a 3 ft (0.91 m) bone near an arroyo, took a piece to Austin, and the two identified it as a pterosaur fossil. Its wingspan was later estimated at over 10 m (33 ft). Lawson first called it "Pteranodon gigas" in a 1972 thesis, but the International Code for Zoological Nomenclature (ICZN) does not accept a thesis as a published work, so it is not a valid name. In 1975 Lawson announced the discovery in the journal Science, calling it "without doubt the largest flying animal presently known." He named the genus after the Aztec feathered serpent god Quetzalcōātl. The specific name honors John Knudsen Northrop, founder of Northrop Corporation, whose large tailless Northrop YB-49 aircraft designs looked somewhat like the animal. The discovery was reported widely, including in Time Magazine, and it appeared on the cover of Scientific American in 1981.

Langston later returned to the area many times and found more bones, including a site called Pterodactyl Ridge where many smaller specimens were found. In 1996 Langston and Alexander Kellner, a azhdarchid expert, published a paper on the skull. Langston died in 2013 before a full description was published. In 2021 a comprehensive description appeared as the 19th memoir of the Society of Vertebrate Paleontology in the Journal of Vertebrate Paleontology. It named the smaller animal Quetzalcoatlus lawsoni after Lawson. Naming was also complicated because the 1975 paper did not give a full description, which made the name hard to accept for decades. A 2019 decision by the ICZN approved a petition that formalized Quetzalcoatlus northropi as the type species. The type specimen, TMM 41450-3, is a partial wing from the Javelina Formation. Scientists have also studied Late Cretaceous relatives from other places, including Hatzegopteryx, a giant relative from Romania, noted by Mark Witton and colleagues, and the newer genus Wellnhopterus, which was named in 2021. Some remains once linked to Quetzalcoatlus, such as those from Alberta and Montana, were later placed in new genera like Cryodrakon, Montanazhdarcho, and Infernodrakon.

Description

Quetzalcoatlus northropi was among the largest azhdarchids, sharing that size with Arambourgiania and Hatzegopteryx (and possibly Cryodrakon). Azhdarchids fall into two main groups: short-necked taxa with short, sturdy beaks, such as Hatzegopteryx and Wellnhopterus, and long-necked taxa with longer, slimmer beaks, such as Zhejiangopterus. Quetzalcoatlus belongs to the long-necked group. Based on its limbs, its relatives, and azhdarchid tracks from South Korea, it was likely quadrupedal, meaning it walked on four legs. Like other pterosaurs, it was covered in hair-like filaments called pycnofibres and had large wing-membranes stretched along a long wing finger. Its wings were broad, with a membrane called the brachiopatagium running from the wing finger tip to the outer side of each ankle. The aspect ratio of its wings is 8.1, similar to storks and birds of prey that soar, relying on thermals, updrafts, and other air currents to gain height through lift and stay in the air.

See also: Pterosaur size

Quetzalcoatlus is one of the largest pterosaurs, but its exact size is hard to know. In 1975, Douglas Lawson compared its wing bones with those of Dsungaripterus and Pteranodon and estimated a wingspan of about 15.5 m (51 ft). Later estimates varied a lot. Robert T. Bakker argued in his 1988 book The Dinosaur Heresies that it may have been even larger, while more recent estimates place its wingspan at 10–11 m (33–36 ft), close to the most that azhdarchids could reach. Much larger wingspans would strain its long bones and joints and make flight very hard. Body mass estimates have also changed, and most since the 2000s are about 200–250 kg (440–550 lb). Gregory S. Paul and Crawford Greenewalt were among the scientists who made these estimates. In a 2025 study, Emily Thomas and Skye N. McDavid revised the wider Azhdarchomorpha group and found Quetzalcoatlus to be polyphyletic, with Q. lawsoni not grouping with the type species Q. northropi. Complete skulls are not known, so the skull of Q. lawsoni is pieced together from several specimens. Based on the lower jaw (mandible), it likely measured about 94–96 cm (37–38 in). Its long, slender beak had no teeth and was built from the premaxilla, maxilla, and dentary. A crest at the base of the beak, a sagittal crest, was formed from the premaxilla. A large skull opening, the nasoantorbital fenestra, combined the nasal cavity and antorbital fenestra. The small, low eye socket, or orbit, allowed some stereoscopic vision, and turning its head and neck gave a field of vision of about 180 degrees. The jugal bone was unusually thick, which may have helped the beak be used in agonistic (fighting) behaviors. The neck had nine long cervical vertebrae and could swing left and right through about 180 degrees. The torso was small, and the first four dorsal vertebrae were fused into a notarium that supported the shoulder girdle in flight. The scapulocoracoid, sternum, and humerus (upper arm bone) were all built for strong flight, and the wing finger was much longer than the other fingers. The pelvis had fused bones, including the ilium, pubis, and ischium. Differences between males and females may be shown in one pelvis, similar to those seen in Darwinopterus, Anhanguera, and Nyctosaurus (see differences between males and females). The femur was among the sturdiest bones, and the feet were narrow and walked plantigrade, meaning the whole sole touched the ground. The claws were moderately curved and sat on well-developed unguals.

Classification

Scientists have grouped Quetzalcoatlus in different ways over the years. In 1975, Douglas Lawson and Crawford Greenewalt did not place it in a more specific group than Pterodactyloidea. In 1984, Kevin Padian first named a family for it and related animals, then in 1986 he changed the grouping to the family Azhdarchidae. Later, in 2014, Andres, James Clark and Xing Xu named a new subfamily, Quetzalcoatlinae, with Quetzalcoatlus as its type genus.

The relationship between Quetzalcoatlus and other giant azhdarchids is still uncertain. Results have changed from study to study. In 2021, Brian Andres found it closely related to Arambourgiania, while a 2022 study placed it with Cryodrakon. A 2025 study by Emily R. Thomas and Skye N. McDavid found that Quetzalcoatlus may not form a single group, with the type species Q. northropi related to Thanatosdrakon.

Paleobiology

Azhdarchids are the only group of pterosaurs that scientists have confidently linked to fossil footprints. Haenamichnus, found in South Korea, has foot shape, age, and size that match azhdarchids, and most of its makers probably had a wingspan of about 5–6 m (16–20 ft). One long trackway shows that azhdarchids held their legs straight under their bodies, which, along with their feet, suggests they were better on the ground than other pterosaurs. Quetzalcoatlus likely walked with a pacing gait, in which the legs on one side of the body moved at about the same time, followed by the legs on the other side.

Scientists understood how giant azhdarchids like Quetzalcoatlus flew only poorly until serious studies were done in the 21st century. In 1984, Paul MacCready built a model flying machine, or ornithopter, with a simple computer acting as an autopilot, and it flew by soaring and flapping its wings. In 2010, Donald Henderson argued that the animal was too heavy for powered flight and may have been flightless. Other researchers disagreed, suggesting it was built for long, powerful flights, and that it may have used thermal soaring after a short burst of flight. Scientists also disagree about how Quetzalcoatlus took off. Some believed it launched mainly with its front legs, while others, including a 2021 study, suggested its back legs were strong enough to lift its body off the ground. A large breastbone would have supported the muscles needed for flight, and John Conway and his co-authors supported a model in which the back legs spread out during flight.

Paleoecology

Fossils of Quetzalcoatlus have only been definitely found in the Javelina Formation of Texas, though similar animals are known from single bones across North America. This rock layer is about 140 m (460 ft) thick and is made of fluvial (river) deposits from the middle to late Maastrichtian. It is slowly covered by the Black Peaks Formation, which contains the Cretaceous–Paleogene boundary. The large sauropod Alamosaurus dominates the animals found here, and it is seen as typical of the Lancian of southern Laramidia. Quetzalcoatlus is the most common vertebrate in the upper half of the formation. Dating with magnetostratigraphy and uranium–lead dating shows these rocks are from about 67 to 66 million years ago. The oldest pterosaur fossil belongs to the azhdarchid Wellnhopterus.

The animals lived in different places. Q. northropi was found in facies of sandstone and conglomerate, which are stream-channel deposits with fish, turtles, crocodilians, and gastropods found nearby. The streams were ephemeral, flowing only for short periods. Q. lawsoni was mostly found in old channel lakes, where the rocks are covered with calcite and carbonates that suggest alkaline lakes. Around these waters grew a warm, dry forest of araucariaceaen conifers, with wood eaten by termites, and palm fronds. Lake animals included invertebrates such as crustaceans, insects, annelids, and bivalves. Q. lawsoni may have eaten these animals and had a body like modern cranes and storks. The forest was evergreen or semideciduous, and Q. northropi likely lived along riparian areas, possibly alone.

Scientists have debated how Quetzalcoatlus fed. In 1975, Douglas Lawson suggested it was a scavenger like a vulture, since it was found with Alamosaurus skeletons, but David Martill disagreed. Later ideas included eating fish like skimmers, probing burrows, or stalking small land animals. Gregory S. Paul suggested in a paper in Nature that it was like storks catching small animals, and Sankar Chatterjee supported this idea. Mark Witton and Darren Naish later suggested that azhdarchids were most like storks or ground hornbills, which catch prey on land. In 2021, Claudio Labita and David Martill suggested they may have been less land-based. Pterosaurs may have declined in variety before becoming extinct, and some researchers linked this to the Chicxulub impact and the Signor-Lipps Effect. Pterosaurs had niche-partitioning, and their extinction opened space for birds to undergo an evolutionary radiation in the Early Cenozoic.

Other animals of the Javelina Formation include the ceratopsids Bravoceratops and Torosaurus utahensis, hadrosaurids such as Gryposaurus and Kritosaurus, Saurolophinae, ankylosaurs, and Tyrannosaurus. Smaller theropods included Saurornitholestes, a dromaeosaurid, and a troodontid. Fish included the stingray Dasyatis, the bowfin, and the gar Atractosteus. Reptiles included a frog, the lizard Glyptosaurus, the snake Dunnophis, and the crocodile Brachychampsa. Small mammals were common, including multituberculates like Ptilodus, Mesodma, Stygimys, and Viridomys, and metatherians such as Peratherium, Bryanictis, Mixodectes, Palaechthon, Eoconodon, and Carsioptychus. Many of these small animals were found by sorting through microfossil sites.

Cultural significance

In 1975, artist Giovanni Caselli drew 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. For the next twenty-five years, before new discoveries were made, it would appear in similar pictures, 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 built a half-scale model weighing 18 kg (40 lb), with a wingspan of 5.5 m (18 ft). The model is on display at the National Air and Space Museum. In 2010, life-sized models of Q. northropi were shown on London's South Bank for the Royal Society's 350th-anniversary exhibition, to help build public interest in science. The models were created by scientists from the University of Portsmouth.