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Pterosaurs

Aundrea Westfall, Auburn University
Pteranodon Reconstruction
The order Pterosauria includes almost 200 species of flying reptiles that co-existed with the dinosaurs from the Upper Triassic to the end of the Cretaceous Period (228 to 66 million years ago). Pterosaurs have been discovered across the world on every continent, even Antarctica. This abundance is a reflection of the wide diversity in the order, their ability to cover vast distances, and a lack of competition for niches by other animal species. They have been found in particularly high numbers in the Midwestern United States, France, United Kingdom, and East Asia. Some genera, like Ornithocheirus, have been found worldwide. Many people believe pterosaurs were dinosaurs, but they are actually just a closely related group of reptiles. The name "pterosaur" is Latin and translates to "winged lizard"; they were so named for this most notable feature of the order. Although many people refer to the entire group as "pterodactyls," that name technically only refers to the members of a single genus, Pterodactylus. Only specimens of the genus Pteranodon have been uncovered in Alabama, specifically in the Mooreville Chalk Formation, and come from the late Cretaceous Period.
Pterosaur Wing Diagram
Pterosaurs' best-known and key feature is their set of wings, which were characterized by a thin membrane of skin, muscle, fibrous tissue, and a complex circulatory system stretching from their body to the tip of an elongated fourth finger. Some wing membranes also incorporated the first three fingers. Also unique to pterosaurs is a bone called the pteroid, which connected to the wrist and helped support the wing membrane between the wrist and shoulder. Many paleontologists debate whether the membrane extended along the body to the hind limbs or not. Based on the variety in the known proportions of pterosaur limbs and the body plans of modern bats and flying squirrels, there was likely a considerable variety in wing plans among species. There is evidence that some pterosaurs had a membrane reaching the hind limbs but others did not. Their mechanism of takeoff is widely debated, with some scientists suggesting that they were able to lift directly off a structure, such as the ground, by flapping their wings like a bird, and others believing that they flung themselves into the air like a flying squirrel. Once in the air, they likely were capable of speeds up to 75 mph (120 kilometers per hour) and could travel thousands of miles at a time.
Much like birds, pterosaurs filled a wide range of niches. There is evidence of both diurnal and nocturnal species, as well as species that specialized in eating prey animals or fish and filter-feeders, much like a flamingo. While most people think of pterosaurs as largely aerial creatures, their hips, femurs, and preserved tracks indicate that they were adept at land locomotion as well, having an erect, energy-efficient stance close to that of mammals. The families Azdharchidae and Ornithocheiridae have relatively long forelimbs that are similar in size and shape to mammals like horses or cows and long hind limbs adapted for increased stride length. Although they likely did not run they certainly were able to move quickly and efficiently. Their feet also show evolutionary patterns similar to birds, with some species having smaller feet that were better adapted to solid, dry ground and others having large feet adapted to walking on soft mud.
Pteranodon Skeleton
Traditionally, paleontologists have divided pterosaurs into two groups: long-tailed rhamphorhynchoids and short-tailed pterodactyloids, but these classifications did not accurately reflect their evolutionary relationships. According to current research, there are 153 accepted genera encompassing 192 species. Some well-known genera include: Pterodactylus, the name often attributed to all pterosaurs; Pteranodon, recognizable for its large cranial crest; Rhamphorhynchus, which featured a long tail and prominent teeth; and Hatzegopteryx, the largest known flying creature, with a wingspan estimated at 33 feet (10 meters). The diversity of pterosaur fossils declines in the Cretaceous, and it is a common misconception that the decline was the result of out-competition by newly emerging bird species. The decrease is in fact not a decline, but rather a more sudden disappearance of many species due to a lack of adequate fossil sites for the later time period. Considering the mostly poor fossil record for both birds and pterosaurs, pterosaurs were probably much more diverse than the current evidence reveals. The record also indicates that birds did not diversify to fill pterosaur niches until after the latter's extinction.
In Alabama, pterosaurs are represented by just a few fragmentary specimens recovered from the Mooreville Chalk Formation in Greene County. One notable fossil was a 3-cm femur of a fledgling found by paleontologist and author Caitlin R. Kiernan in February 1983. Remains of young specimens are very rare, and this is the only fossil of a subadult pterosaur collected from the eastern United States. Although all the specimens are too incomplete to make a definite identification, they are most consistent with the genus Pteranodon and are likely from between the Santonian and Campanian stages of the late Cretaceous (85.8 to 70.6 million years ago). The name Pteranodon means "winged and toothless" because, unlike many early pterosaurs, these animals had toothless beaks most likely used for catching fish. This genus includes some of the largest members of Pterosauria, with wingspans reaching 18 to 24 feet (5.6 to 7.3 meters) in males, although females commonly stretched only around 12 feet (3.8 meters) on average. Other distinguishing characteristics include the cranial crest, relatively short tail, and narrow neural spines.
Resources
Barrett, Paul M., Richard J. Butler, Nicholas P. Edwards, and Andrew R. Milner. "Pterosaur Distribution in Time and Space: An Atlas." Zitteliana B 28 (December 2008): 61-107.
Butler, Richard J., Paul M. Barrett, Stephen Nowbath, and Paul Upchurch. "Estimating the Effects of Sampling Biases on Pterosaur Diversity Patterns: Implications for Hypotheses of Bird/Pterosaur Competitive Replacement." Paleobiology 35 (September 2009): 432-46.
Unwin, David M. The Pterosaurs: From Deep Time. New York: Pi Press, 2006.
Witton, Mark P. Pterosaurs: Natural History, Evolution, Anatomy. Princeton, N.J.: Princeton University Press, 2013.
Published:  November 21, 2016   |   Last updated:  June 30, 2015