Science / Medicine : Oldest Dinosaur Shows Off a New Trick : Evolution: A discovery 230 million years old surprises scientists with its sophisticated features, including a double-hinged jaw.
The oldest known dinosaur has been discovered by a University of Chicago paleontologist in the foothills of the Andes Mountains near San Juan, Argentina. The dinosaur is surprising, according to its discoverer, Paul Sereno, because, despite its position in the early stages of dinosaur evolution, it is “sophisticated and well-evolved.”
Sereno described the dinosaur, called Herrerasaurus , for the first time last week at a meeting of paleontologists in Austin, Tex. The complete skeleton of the dinosaur, which Sereno and his colleague, Alfredo Monetta of the Argentine Museum of Natural Science in San Juan, recovered from the sandstone deposits of the Ischigualasto Formation, is now being prepared for display at the museum.
Herrerasaurus, which roamed the region 230 million years ago, was about six to eight feet long and weighed nearly 300 pounds, Sereno said in a telephone interview. The skeleton shows that its neck was surprisingly slender and that its skull was narrow and bird-like. It had enormous claws and small forelimbs, indicating that it spent much of its time walking on its hind limbs.
Its most unusual feature is that the bottom of its jaw is doubly hinged--once at the normal spot in the rear and once in the middle. The second hinge would allow the jaw to close completely around a prey that was too large to swallow whole.
“To see that (jaw) so well-developed was really quite surprising,” Sereno said. “It suggests that this animal was a very active predator, going after live, struggling types of prey.”
He noted that such a hinged jaw did not appear in other types of dinosaurs until 50 to 100 million years later. This fact leads him to conclude that Herrerasaurus was not a direct ancestor of later dinosaurs, but that it was “a little branch off the line that led to dinosaurs.”
Because the Herrerasaurus was so small and lightly built, Sereno said in a telephone interview from Austin, “it is a miracle we found an intact skeleton. We found little, tiny ear bones and even little plates in the iris of the eyes. The detail suggests that the animal died near the bed of a river and got covered up rather quickly so that it was pretty whole when it was buried.”
Sereno plans to go back to Argentina this summer and search the Ischigualasto Formation for predecessors of Herrerasaurus. He and Monetta already have found some two-foot long animals that are closely related to it, and he hopes to find remains of still-smaller specimens.
