Quetzalcoatlus

Animalia

Quetzalcoatlus northropi Temporal range: Late Cretaceous, 68–65.5 Ma PreЄ Є O S D C P T J K Pg N ↓
Reconstructed skeleton
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	†Pterosauria
Suborder:	†Pterodactyloidea
Family:	†Azhdarchidae
Genus:	†Quetzalcoatlus Lawson, 1975
Species:	†Q. northropi
Binomial name
Quetzalcoatlus northropi Lawson, 1975
Synonyms
Hatzegopteryx thambema? Buffetaut, Grigorescu & Csiki, 2002

Quetzalcoatlus (/kwɛtsəlkoʊˈætləs/) was a pterodactyloid pterosaur known from the Late Cretaceous of North America (Maastrichtian stage, about 68–65.5 million years ago), 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. Its name comes from the Mesoamerican feathered serpent god Quetzalcoatl.

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 from another 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.

Size

See also: Pterosaur size

Size comparison of Q. northropi (green), the unnamed smaller species (blue), 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 15.9 meters (52.2 feet), choosing the middle of three extrapolations from the proportions of other pterosaurs that gave an estimate of 11, 15.5 and 21 meters respectively (36 feet, 50.85 feet, 68.9 feet). In 1981, further study lowered these estimates to 11–12 meters (36–39 feet). 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 in consequence published results vary widely. While some studies have historically found extremely low weight estimates for Quetzalcoatlus, as low as 70 kilograms (150 lb) for a 10-meter individual, a majority of estimates published since the 2000s have been higher, and the tend toward 200–250 kilograms (440–550 lb).

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 (dated to around 68 million years ago) in 1971 by a geology graduate student from the University of Texas at Austin's Jackson School of Geosciences, Douglas A. Lawson. The specimen consisted of a partial wing (in pterosaurs composed of the forearms and elongated fourth finger), from an individual later estimated at over 10 m (33 ft) in wingspan. Lawson discovered a second site of the same age, about forty kilometers from the first, where between 1972 and 1974 he and Professor Wann 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. 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 flying wing aircraft designs resembling Quetzalcoatlus. 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. 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).

The holotype specimen of Q. northropi has yet to be discovered and described. Where the known remains overlap, it has been considered by Mark Witton and colleagues (2010) to be indistinguishable from its Romanian contemporary Hatzegopteryx. If Q. northropi is complete enough to be distinguished from other pterosaurs (i.e., if it is not a nomen dubium), Hatzegopteryx may represent the same animal. It is likely that huge pterosaurs such as Q. northropi would have had very large, transcontinental ranges, making its presence in both North America and Europe unsurprising. Mark Witton et al. pointed out that the skull material of Hatzegopteryx and Q. sp. differ enough that they cannot be regarded as the same animal, making it likely that Q. sp., if not identical to Quetzalcoatlus northropi, represents a distinct genus.

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, the vertebra shows no evidence that it was chewed 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).

Paleobiology

Quetzalcoatlus was abundant in Texas during the Lancian in a fauna dominated by Alamosaurus. The Alamosaurus-Quetzalcoatlus association probably represents semi-arid inland plains. Quetzalcoatlus had precursors in North America and its apparent rise to widespreadness may represent the expansion of its preferred habitat rather than an immigration event, as some experts have suggested.

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 four hundred kilometers removed from the coastline and there were no indications of large rivers or deep lakes nearby at the end of the Cretaceous, 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 jaw bent so strongly downwards that even when it closed completely a gap of over five centimeters remained between it and the upper jaw, 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. 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 the energy costs would be too high due to excessive drag. 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 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 azhdarchids 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.

Flight

Artist's impression of an individual in flight

The nature of flight in Quetzalcoatlus and other giant azhdarchids is poorly understood. Their method of flight depends largely on their weight, which has been controversial, with widely differing masses 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. In 2010, Donald Henderson argued that the mass of Q. northropi has been underestimated, even the highest estimates, and that it was too massive to have achieved powered flight. Henderson argued that it may have been flightless.

Paul MacCready undertook an aerodynamics experiment testing the flight of Quetzalcoatlus in 1986. He constructed a model flying machine or ornithopter with a simple computer functioning as an autopilot. The model successfully flew with a combination of soaring and wing flapping; however, the model was half scale based on a then-current weight estimate of around 80 kg, far lower than more modern estimates of over 200 kg. (Also, see below.)

In popular culture

Models in South Bank for the Royal Society's 350th anniversary exhibition

Quetzalcoatlus has been featured in documentaries, both in cinemas and on television, since the 1980s. The Smithsonian project to build a working model of Q. northropi was the subject of the 1986 IMAX documentary On the Wing, shown at the National Air and space museum in Washington, D.C.. It has also been featured in television programs such as the BBC's Walking with Dinosaurs in 1999 and Dangerous, Ltd.'s Clash of the Dinosaurs in 2009. The later program featured traits invented by the producers to heighten entertainment value, including a depiction of Quetzalcoatlus with the ability to use ultraviolet vision to locate dinosaur urine when hunting in the air. It was also depicted in the 2011 documentary March of the Dinosaurs, where it was erroneously depicted as a clawless, bipedal scavenger, and in the 2009 series Animal Armageddon, where it was correctly portrayed with pycnofibres.

In June 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 30 feet (9.1 m), were intended to help build interest in science among the public. The models were created by scientists from the University of Portsmouth, including David Martill, Bob Loveridge and Mark Witton, and engineers Bob and Jack Rushton from Griffon Hoverwork. The display presented to the public the most accurate pterosaur models constructed at the time, taking into account anatomical and footprint evidence based on skeletal and trace fossils from related pterosaurs.

In modern technology designs

In 1985, the U.S. Defense Advanced Research Projects Agency (DARPA) and AeroVironment used Quetzalcoatlus northropi as the basis for an experimental ornithopter UAV. They produced a half-scale model weighing 40 pounds (18 kg), with a wingspan of 18 feet (5.5 m). Coincidentally, Douglas A. Lawson, who discovered Q. northropi in Texas in 1971, named it for John "Jack" Northrop, a famous 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.