Quetzalcoatlus

Quetzalcoatlus Fossil range: Late Cretaceous, 70–65.5 Ma PreЄ Є O S D C P T J K Pg N ↓
Reconstruction of a Quetzalcoatlus skeleton
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Pterosauria
Suborder:	Pterodactyloidea
Family:	Azhdarchidae
Genus:	Quetzalcoatlus Lawson, 1975
Species
Q. northropi Lawson, 1975 (type) Q. sp. vide Kellner & Langston, 1996

Quetzalcoatlus was a pterodactyloid pterosaur known from the Late Cretaceous of North America (Maastrichtian stage, 70–65.5 ma), and one of the largest known flying animals of all time. It was a member of the Azhdarchidae, a family of advanced toothless pterosaurs with unusually long, stiffened necks.

Description

Skull material (from the unnamed smaller species) shows that Quetzalcoatlus had a very sharp and pointed beak, contrary to some earlier reconstructions that showed a blunter snout, based on the inadvertent inclusion of jaw material of an other pterosaur species, possibly a tapejarid or a form related to Tupuxuara. A skull crest was present but its exact form and size are still unknown.^[1]

Size

Size comparison of the two known Quetzalcoatlus species and a human

When it was first discovered, scientists estimated that the largest Quetzalcoatlus fossils came from an individual with a wingspan as large as 15.5 meters, choosing the middle of three extrapolations from the proportions of other pterosaurs that gave an estimate of 11, 15.5 and 21 meters respectively. In 1981, further study lowered these estimate to 11-12 meters (36-39 feet).^[2] More recent estimates based on greater knowledge of azhdarchid proportions place its wingspan at 10-11 meters (33-36 ft).

Mass estimates for giant azhdarchids are extremely problematic because no existing species share a similar size or body plan, and as a result published results vary widely.^[3] A 2002 study suggested a body mass of 90–120 kilograms (200–260 lb) for Quetzalcoatlus, considerably lower than most other recent estimates.^[4] Higher estimates tend toward 200–250 kilograms (440–550 lb).^[5]

The issue of the size of Quetzalcoatlus is related with the question what the upper size limit for animal flight might be and whether Quetzalcoatlus might have reached it. However, such claims once also accompanied the discovery of large (perhaps up to 9 m (30 ft)) Pteranodon. The azhdarchid Hatzegopteryx has been estimated to possibly be slightly larger than Quetzalcoatlus.^[6]

Discovery and species

Restored skeleton in quadrupedal stance

The first Quetzalcoatlus fossils were discovered in Texas (from the Maastrichtian Javelina Formation at Big Bend National Park) in 1971 by geology graduate student Douglas A. Lawson. The specimen consisted of a partial wing (made up of the forearms and elongated fourth finger in pterosaurs), from an individual later estimated at over to 10 m (33 ft) in wingspan.^[3] Lawson discovered a second site of the same age, about forty kilometer from the first, where between 1972 and 1974 he and Professor Winn Langston Jr. of the Texas Memorial Museum unearthed three fragmentary skeletons of much smaller individuals. Lawson in 1975 announced the find in an article in Science.^[7] That same year, in a subsequent letter to the same journal he made the original large specimen, TMM 41450-3, the holotype of a new genus and species, Quetzalcoatlus northropi. The genus name refers to the Aztec "feathered serpent" god Quetzalcoatl. The specific name honors John Knudsen Northrop, the founder of Northrop, who was interested in large tailless aircraft designs resembling Quetzalcoatlus.^[8] At first it was assumed that the smaller specimens were juvenile or subadult forms of the larger type. Later, when more remains were found, it was realized they could have been a separate species. This possible second species from Texas was provisionally referred to as a Quetzalcoatlus sp. by Alexander Kellner and Langston in 1996, indicating that its status was too uncertain to give it a full new species name.^[1] The smaller specimens are more complete than the Q. northropi holotype, and include four partial skulls, though they are much less massive, with an estimated wingspan of 5.5 meters (18 ft).^[6]

Skull reconstruction of Q. sp.

An azhdarchid neck vertebra, discovered in 2002 from the Maastrichtian age Hell Creek Formation, may also belong to Quetzalcoatlus. The specimen (BMR P2002.2) was recovered accidentally when it was included in a field jacket prepared to transport part of a tyrannosaur specimen. Despite this association with the remains of a large carnivorous dinosaur, it shows no evidence that it was fed on by the dinosaur. The bone came from an individual azhdarchid pterosaur estimated to have had a wingspan of 5 - 5.5m (16.5 - 18 ft).^[9]

In 1995, a partial skeleton of a juvenile azhdarchid was discovered in Dinosaur Provincial Park, probably from Quetzalcoatlus or another closely related animal. The carcass had been scavenged by the small dromaeosaurid Saurornitholestes, which broke off a tooth on one of the wing bones. ^[10]

Paleobiology

Feeding

Artist's impression of a group feeding on the ground

There have been a number of different ideas proposed about the lifestyle of Quetzalcoatlus. Because the area of the fossil site was at the end of the Cretaceous four hundred kilometers removed from the coastline and there were no indications of large rivers or deep lakes, Lawson in 1975 rejected a fish-eating lifestyle, instead suggesting that Quetzalcoatlus scavenged like the Marabou Stork, but then on the carcasses of titanosaur sauropods such as Alamosaurus. Lawson had found the remains of the giant pterosaur while searching for the bones of this dinosaur, which formed an important part of its ecosystem.

In 1996, Thomas Lehman and Langston rejected the scavenging hypothesis, pointing out that the lower jaws bent so strongly downwards that even when they closed completely a gap of over five centimeters remained with the upper jaws, very different from the hooked beaks of specialized scavenging birds. They suggested that with its long neck vertebrae and long toothless jaws Quetzalcoatlus fed like modern-day skimmers, catching fish on the wing while cleaving the waves with its beak.^[11] While this skim-feeding view became widely accepted, it was not subjected to scientific research until 2007 when a study showed that for such large pterosaurs it was not a viable method because due to excessive drag the energy costs would be too high.^[12] In 2008 pterosaur workers Mark Paul Witton and Darren Naish published an examination of possible feeding habits and ecology of azhdarchids. Witton and Naish noted that most azhdarchid remains are found in inland deposits far from the seas or other large bodies of water required for skimming. Additionally, the beak, jaw, and neck anatomy are unlike those of any known skimming animal. Rather, they concluded that azhdarchis were more likely terrestrial stalkers, similar to modern storks, and probably hunted small vertebrates on land or in small streams. Though Quetzalcoatlus, like other pterosaurs, was a quadruped when on the ground, Quetzalcoatlus and other azhdarchids have fore and hind limb proportions more similar to modern running ungulate mammals than to their smaller cousins, implying that they were uniquely suited to a terrestrial lifestyle.^[3]

Flight

Artist's impression of an individual in flight

Studies have shown that Quetzalcoatlus could take off under its own power, but once aloft it may have spent much of its time soaring. To test the flight on Quetzalcoatlus, a program sponsored by Johnson Wax involved the construction of a model flying machine[1]. It was about half scale (20 ft), the size of Quetzalcoatlus sp., and had a simple computer functioning as an autopilot. The experiment worked and the model flew through the skies with a combination of soaring and wing flapping. The model is now resting in the Smithsonian Institution Air and Space Museum.

Environment

During the Cretaceous period, Texas's climate was similar to modern tropical coastal wetlands and lagoons, extending along the Cretaceous Seaway that filled the center of North America. Bones of related animals are also known from Dinosaur Provincial Park, Alberta, Canada.

Being found in layers that are only slightly older than the Cretaceous–Tertiary extinction event, Quetzalcoatlus probably became extinct at the end of the Cretaceous period along with the dinosaurs.

In popular culture

Quetzalcoatlus was the star of the 1986 IMAX movie On the Wing where a half sized robot version engineered by AeroVironment demonstrated primitive flight. Also has been featured in the nature documentary Walking with Dinosaurs episode "Death of a Dynasty", the third episode of Dinosaur Planet, When Dinosaurs Roamed America, episode 5 (Late Cretaceous), and episodes of Animal Armageddon.

There is a fictional species of Quetzalcoatlus known as Skybax in the Dinotopia series.

See also

• Pterosaur size

References

External links

Paleontology portal

• Quetzalcoatlus northropi - A pterosaur from the Upper Cretaceous (pdf)
• Model flying machine of Quetzalcoatlus northropi by AeroVironment, Inc