Quetzalcoatlus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Pterosauria

Family: Azhdarchidae

Genus:Quetzalcoatlus

Species:Quetzalcoatlus northropi

Introduction

Quetzalcoatlus was a flying reptile living in North America during the Late Cretaceous. Named for the wrathful feathered serpent Aztec god Quetzalcóatl, the Quetzalcoatlus in one of the largest flying reptiles ever discovered. The fossils of Quetzalcoatlus fueled an ongoing debate about the weight limits in flying animals and the evolution of powered flight in the animal kingdom.

Flying reptiles occupied vast areas during the Late Triassic, when the world's continents were united in a single landmass, called Pangaea. Tectonic activity eventually caused the supercontinent to break into two supercontinents, Gondwanaland in the south and Laurasia in the north. By the Late Cretaceous, the continents were dividing further and approaching their present configuration, while groups of prehistoric reptiles and dinosaurs diversified on the now-isolated landmasses.

Quetzalcoatlus was part of a lineage of pterosaurs that arrived in North America during the Jurassic and diversified into a number of species. Related species have been found in portions of Europe and Asia, suggesting that the group diversified after arriving in Laurasia.

Classification

Scientists use two primary methods to divide organisms into groups. Linnaean taxonomy classifies organisms based on overall physical similarity while an alternate method, called “cladistics,” created groups, or “clades,” based on the evolutionary relationships between species. Cladistics attempts to trace evolutionary relationships by tracing the inheritance of a key trait between related species.

Linnaean taxonomy places Quetzalcoatlus into the order Pterosauria, a group that includes all of the flying reptiles of the Mesozoic era that evolved alongside the dinosaurs. Further, Quetzalcoatlus was placed in the Pterodactyloidea, a group united by the presence of short tails and long, usually toothless, beaks.

Cladistic analysis also uses the Pterosauria clade, defined by the development of wings formed from skin stretched between the fingers of the hand and the rear legs. Cladistics also uses the grouping Azhdarchoidea, which are grouped according to unique features of the spine and skull. The family Azhdarchidae is also a clade, defined by the development of unique bones in the neck and spine.

Quetzalcoatlus and other members of the clade Azhdarchoidea and family Azhdarchidae were among the largest of the pterosaurs and among the largest flying vertebrates from any animal group. Quetzalcoatlus, like other members of this group, had a long, toothless beak and a stiff, long neck.

Anatomy

Quetzalcoatlus was a large pterosaur with a wingspan of between 10 and 12 meters (33 to 39 feet) but lightly built for its size. Estimates of its adult weight range between 75 to 544 kilograms. Despite that, it contained large air sacs and had stiff, thin-walled hollow bones. Walking on four legs, it reached a height of between 2.9 to 3 meters (8 to 9 feet). The animal's wings consisted of a delicate membrane of skin stretched between the elongated fourth finger of each hand and the hind legs.

Quetzalcoatlus had a thin head, which may have been as long as 2 meters (6.5 feet) or more and may have had an elongated crest, and a long, thin, and toothless beak. Skin impressions from pterosaurs indicate a covering of skin or fine hair, though no remains of Quetzalcoatlus have so far given indication as to the animal's covering.

Intelligence

University of Chicago paleontologist James A. Hopson used the ratio of an animal's brain to body mass, called the encephalization quotient (EQ), to measure intelligence. Estimates for dinosaurs indicate that the majority fell within a range of 0.1 to 2.0, on a scale that extends to 8.0 (humans have an EQ of 7.44 and dolphins measure a 5.31).

EQ estimates for many pterosaurs fell in the 0.3 to 0.5 range, placing them at the low end of the EQ spectrum compared to dinosaurs. Though Quetzalcoatlus lived a similar lifestyle to large modern birds that live and hunt near open water, the animal had considerably lower EQ ratings, suggesting that the pterosaurs may not have been as intelligent as modern birds.

Reproduction and Population

Paleontologists have found eggs in close association to the nests of some flying reptiles, suggesting that at least some pterosaurs were ovoviviparous. Paleontologists have suggested that some species may have been viviparous, giving birth to live young. A 2010 discovery of a pterodactyl egg and fossil, a Darwinopterus (a genus of pterosaur dating back to the Middle Jurassic) named “Mrs. T,” indicates sexual dimorphism. The fossil, found with an egg, provides direct evidence that females were crestless and had wider hips. Scientists indicate that this find will help in future research relative to sex among pterosaurs. The discovery of the egg also indicates that shells were small and soft (in contrast to eggs laid by modern-day birds), which scientists speculate would require less energy to produce, giving pterosaurs an “evolutionary advantage.” Some paleontologists believe that pterosaurs provided some parental care to their young, though conclusive evidence is lacking.

Quetzalcoatlus is only known from a few isolated specimens, and paleontologists have been unable to determine population size. Evidence from other pterosaurs indicates that some may have gathered in groups. Paleontologists are uncertain as to whether these gatherings indicate some form of communal nesting, as seen in many types of birds.

Diet

Quetzalcoatlus possessed a long powerful beak that was sharp enough to allow it to feed on meat and other animals. Most paleontologists agree that Quetzalcoatlus was predatory.

Some paleontologists have suggested that Quetzalcoatlus behaved much like modern pelicans, soaring above seas and lakes and taking fish and other animals from the surface; the stiffness of its neck and thus limited range of motion would have made high-speed fishing difficult, however. Others believe that Quetzalcoatlus may have behaved more like a modern stork or heron, walking in a quadrupedal stance and snatching food from the ground or from the water's edge. The long neck of the azhdarchids may have served as stealth function in hunting.

Behavior

Little is known about the behavior of Quetzalcoatlus. The animal's robust leg and arm bones suggest that it might have spent much of its time walking, perhaps feeding primarily on terrestrial prey. Its long wings and ratio of wing bones suggest that the animal was adapted for soaring on wind currents and not for vigorous flapping.

Flying models reveal that Quetzalcoatlus could take off under its own power, but some paleontologists have suggested that large pterosaurs would have nested on cliffs, where they could dive into the air rather than powering off from the ground. There is no strong evidence to suggest that Quetzalcoatlus gathered in groups or displayed any social behavior.

Habitat and Other Life Forms

Definitive Quetzalcoatlus specimens have been uncovered from Late Cretaceous sediment in North America, with specimens appearing from Texas to Montana. The climate of North America was slightly warmer during the Cretaceous period than in the modern era, and most of central North America was covered in shallow seas surrounded by forests and open scrub plains.

Gymnosperms, like conifers and cycads, were the dominant plant life of the Cretaceous, though angiosperms were beginning to spread around the world, appearing as small shrubs and weeds. In addition to dinosaurs, there were a wide variety of reptiles, amphibians, small mammals, and birds in North America, though pterosaurs were still the dominant flying vertebrates.

The ceratopsians, or “horned dinosaurs” were one the most successful groups of herbivorous dinosaurs in North American, including genera like Triceratops, Styracosaurus, Chasmosaurus, and more than a dozen other species. The hadrosaurs were another highly successful herbivorous dinosaur lineage, including species like Maiasaura and Parasaurolophus. Another common group of herbivores was the pachycephalosaurs, bipedal dinosaurs characterized by bony coverings on their skulls, like Gravitholus and Ornatotholus.

Predatory dinosaurs living at the same time included the carnosaurs, like Tyrannosaurus and Nanotyrannus. There were also a number of smaller predators, including genera like Dromeosaurus and Bambiraptor. Quetzalcoatlus shared the skies with a large variety of other pterosaurs, ranging from small insectivores to large hunters like Pteranodon.

Research

The first Quetzalcoatlus specimen was discovered in 1971 by geologist and paleontologist Douglas Lawson and consisted only of wing fragments. Lawson and colleagues discovered additional skeletal fragments in the late 1970s that gave a better idea of the animal's anatomy. In the 1990s, several specimens of another member of the genus were discovered, though they were smaller than the original specimen.

Engineers and paleontologists cooperated to build a 0.5 scale flying machine replica of Quetzalcoatlus to test and examine the animal's flying abilities. Other studies have seemed to confirm that Quetzalcoatlus and other large pterosaurs may have been capable of powered flight, though they most likely traveled primarily by gliding. Some researchers, such as Sankar Chatterjee, have argued that because of its large mass, the pterosaur would have had to run in order to become airborne. Another theory advanced by Mark Witton and Michael Habib is that Quetzalcoatlus could have used a quadrupedal launch, applying pressure to the ground with all four limbs, to achieve take off. Witton further postulated that Quetzalcoatlus could remain aloft for as long as seven to ten days.

A related azhdarchid was discovered in Alberta, Canada, in 1992 and was eventually identified as a species distinct from Quetzalcoatlus in 2019. Cryodrakon boreas differed from Quetzalcoatlus in the long bone of the upper arm and had a shorter, thicker neck, a heavier build, and an additional hole in its vertebrae.

Bibliography

Carpenter, Kenneth. Eggs, Nests and Baby Dinosaurs: A Look at Dinosaur Reproduction. Indiana UP, 1999.

Chatterjee, Sankar, and R. J. Templin. “Posture, Locomotion and Paleoecology of Pterosaurs.” Geological Society of America Special Papers, vol. 376, 2004, pp. 1–64.

Chinsamay-turan, Anusuya. Microstructure of Dinosaur Bone: Deciphering Biology with Fine-Scale Techniques. Johns Hopkins UP, 2005.

Fastovsky, David E., and David B. Weishampel. Dinosaurs: A Concise Natural History. 3rd ed., Cambridge UP, 2016

Goto, Yusuke, et al. "How Did Extinct Giant Birds and Pterosaurs Fly? A Comprehensive Modeling Approach to Evaluate Soaring Performance." PNAS Nexus, vol. 1, no. 1, 2022, p. 023

Habib, Michael B. “Pterosaurs Were Monsters of the Mesozoic Skies.” Scientific American, Oct. 2019, www.scientificamerican.com/article/pterosaurs-were-monsters-of-the-mesozoic-skies/, 10.1038/scientificamerican1019-26. Accessed 25 Sep. 2024. ‌

Horner, Jack, and James Gorman. How to Build a Dinosaur: Extinction Doesn’t Have to Be Forever. Dutton, 2009.

Horner, John R., and Edwin Dobb. Dinosaur Lives: Unearthing an Evolutionary Saga. Mariner Books, 1998.

“Introduction to the Pterosauria.” UCMP, University of California Museum of Paleontology, www.ucmp.berkeley.edu/diapsids/pterosauria.html. Accessed 25 Sep. 2024. ‌

Lucas, Spencer G. Dinosaurs: The Textbook. 6th ed., Columbia UP, 2016.

Martin, Anthony J. Introduction to the Study of Dinosaurs. 2nd ed., Blackwell, 2006.

Paul, Gregory S. Dragons of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Johns Hopkins UP, 2002.

“Pterosaurs in Big Bend.” Big Bend National Park, Texas, National Park Service, US Dept. of the Interior, 24 Feb. 2015, www.nps.gov/bibe/naturescience/pterosaur.htm. Accessed 25 Sep. 2024. ‌

“Quetzalcoatlus.” Texas Memorial Museum, University of Texas at Austin, www.utexas.edu/tmm/sponsored‗sites/dino‗pit/quetzalcoatlus.html. Accessed Feb. 2010.

Stein, Ross S. “Aerodynamics of the Long Pterosaur Wing.” Science, vol. 191, no. 4230, 1976, pp. 898–99.

Weishampel, David B., et al. The Dinosauria. 3rd. ed., U of California P, 2007.