| Quetzalcoatlus Temporal range: Late Cretaceous (Maastrichtian),
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| Restored Quetzalcoatlus skeleton displayed in quadrupedal stance, Houston Museum of Natural Science | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Order: | †Pterosauria |
| Suborder: | †Pterodactyloidea |
| Family: | †Azhdarchidae |
| Subfamily: | †Quetzalcoatlinae |
| Genus: | †Quetzalcoatlus Lawson, 1975 |
| Type species | |
| †Quetzalcoatlus northropi Lawson, 1975
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| Other species | |
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| Synonyms | |
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Quetzalcoatlus (/kɛtsəlkoʊˈætləs/) is a genus of azhdarchid pterosaur known from the Late Cretaceous Maastrichtian age of North America. The first specimen, recovered in 1971 from the Javelina Formation, consists of several wing fragments. It was made the holotype of Quetzalcoatlus northropi in 1975 by Douglas Lawson and was named after the Aztec serpent god, Quetzalcōātl, and Jack Northrop, designer of tailless fixed-wing aircraft. The remains of a second species were found between 1972 and 1974, also by Lawson, around 40 km (25 mi) from the type of Q. northropi. In 2021, these remains were assigned the name Quetzalcoatlus lawsoni by Brian Andres and (posthumously) Wann Langston Jr.
Quetzalcoatlus northropi has gained fame as a candidate for the largest flying animal ever discovered, though estimating its size has been difficult due to the fragmentary nature of its type specimen. Wingspan estimates over the years have ranged from 5.2–25.8 m (17–85 ft), though this has more recently been narrowed down to around 10–11 m (33–36 ft), based on extrapolations from more complete azhdarchids. The smaller and more complete Q. lawsoni had a wingspan of around 4.5 m (15 ft). Quetzalcoatlus' proportions were typical of azhdarchids. It possessed a very long neck and beak, shortened non-wing digits that were well adapted for terrestrial locomotion, and a very short tail.
While historical interpretations of Quetzalcoatlus' diet have ranged from scavenging to skim-feeding like the modern skimmer bird, it is likely that, like other large azhdarchids, Quetzalcoatlus northropi hunted small prey on the ground, similar to storks and ground hornbills. This has been dubbed the terrestrial stalking model. Q. lawsoni, however, appears to have been associated with alkaline lakes, and a diet of small aquatic invertebrates has been suggested. Similarly, while Q. northropi seems to have been fairly solitary, Q. lawsoni appears to have been highly gregarious.
For years it was uncertain how Quetzalcoatlus took off. Early models using a bipedal stance, such as that of Sankar Chatterjee and R.J. Templin in 2004, were heavily reliant on a relatively light weight (about 70 kg (150 lb) in Chatterjee and Templin's case), and even then, struggled to explain how takeoff was achieved. Based on the work of Mark P. Witton and Michael Habib in 2010, it now seems likely that pterosaurs, especially larger taxa such as Quetzalcoatlus, launched quadrupedally, using the powerful muscles of their forelimbs to propel themselves off the ground and into the air.