The rare pterosaur — literally a winged lizard — is also one of the youngest members in the world of the family Ornithocheiridae, and only the second ornithocheirid ever documented in North America.
The newly-named lizard is described in the Journal of vertebrate Paleontology.
Aetodactylus halli would have soared over what is now the Dallas-Fort Worth area during the Cretaceous Period when much of the Lone Star state was under water, covered by a vast ancient sea. Much of Texas was once submerged under the Western Interior Seaway. The massive sea split North America from the Gulf of Mexico to the Arctic Ocean.
(Photo Credit: Illustration by Karen Carr)
"The ancient sea that covered Dallas provided the right conditions to preserve marine reptiles and other denizens of the deep, as well as the delicate bones of flying reptiles that fell from their flight to the water below," says Louis Jacobs, a professor of earth science at Southern Methodist University. "The rocks and fossils here record a time not well represented elsewhere in North America."
Cretaceous marine environment
(photo credit: Karen Carr)
While rare in North America, toothed pterosaurs belonging to the Ornithocheiridae are a major component of Cretaceous pterosaur faunas elsewhere in the world. The Texas specimen — a nearly complete mandible with most of its 54 teeth missing — is definitively younger than most other ornithocheirid specimens from Brazil, England and China. It is five million years younger than the only other known North American ornithocheirid.
The specimen was found in 2006 in North Texas, embedded in a soft, powdery shale exposed by excavation of a hillside next to a highway. The site was near the city of Mansfield, southwest of Dallas.
The Aetodactylus halli jaw was discovered in the geologic unit known as the Eagle Ford Group, which comprises sediments deposited in a shallow sea. Outcrop of the Eagle Ford Group extends northward from southwestern Texas into southern Oklahoma and southwestern Arkansas.
The 38.4-centimeter Aetodactylus jaw originally contained 54 slender, pointed teeth, but only two remain in their sockets. The lower teeth were evenly spaced and extended far back along the jaw, covering nearly three quarters of the length of the mandible. The upper and lower teeth interlaced when the jaws were closed.
In Aetodactylus, changes in tooth size along the jaw follow a similar pattern to those of other ornithocheirids. However, Aetodactylus differs from all other ornithocheirids in that its jaws were thin and delicate, with a maximum thickness not much greater than 1 centimeter. But the specimen does compare favorably with Boreopterus, a related pterosaur from the Early Cretaceous of China, in terms of the number of teeth present in the lower jaw.
Scientists estimate the wingspan to be around 3 meters, or about 9 feet, indicating Aetodactylus would have been a "medium-sized" pterosaur. While it's not known how Aetodactylus died, at the time of death the reptile was flying over the sea and fell into the water, perhaps while fishing.
North American pterosaurs that date from the Cretaceous are all toothless, except for Aetodactylus and Coloborhynchus. The thinness of the jaws, the upward angle of the back half of the mandible and the lack of a pronounced expansion of the jaw tips indicate that Aetodactylus is different from other ornithocheirids and represents a new genus and species of pterosaur.
"Discovery of another ornithocheirid species in Texas hints at a diversity of pterosaurs in the Cretaceous of North America that wasn't previously realized," says SMU paleontologist Timothy S. Myers. "Aetodactylus also represents one of the final occurrences of ornithocheirids prior to the Late Cretaceous transition to pterosaur faunas that were dominated by the edentulous, or toothless, species."