A team of American and Argentinian paleontologists has discovered the world's oldest dinosaur, an approximately 225,000,000-year-old carnivore that walked on two legs. Eoraptor, or "dawn stealer," lacks nearly all the specialized features found in later dinosaurs. Paul Sereno a scientist that studied the fossil believes this find is very close to the first dinosaur. This fossil is a link between what scientists previously theorized and what the most primitive dinosaurs really looked like.
Sereno named the new genus "dawn stealer" because it appeared at the dawn of the dinosaurs and, though clearly a meat-eater, was not large enough to hunt the herbivorous reptiles common at the time. "It would have been a crafty hunter, probably eating small animals and snatching the young of larger species."
In October, 1991, Sereno and Alfredo Monetta of the National University of San Juan, Argentina, led a dinosaur-hunting trip to Argentina. Student Ricardo Martinez found the fossilized Eoraptor less than a mile from the place where, in 1988, Sereno discovered a nearly complete skeleton of the oldest known dinosaur, Herrerasaurus. The students were walking away from another specimen and Ricardo happened to pick up the skull. There was just a hint of teeth which helped them to realize they were looking at an ancient skull.
They found the fossils and nearly all the bones were in place. The dinosaur was lying on its side and appeared to have been mummified in that position. When that happens the tendons contract and it causes the back to arch.
Sereno says they could tell it was a primitive dinosaur even from the field. For example, the researchers could see the animal's small pelvis and tell that it lacked the flexible jaw that characterizes many carnivorous dinosaurs. Scientists are trying to determine where it fits in dinosaur evolution by looking at the bones and how they relate to other dinosaurs.
Examination of the fossil made it clear that Eoraptor represents an early stage in dinosaur evolution. The skull and body lack most of the characteristics that paleontologists use to group dinosaurs - a finding that indicates that Eoraptor evolved before the branches of the family tree were widely separated. However, some of the fossil characteristics place Eoraptor as an early member of the "theropod" group of dinosaurs, a branch that includes Herrerasaurus and Tyrannosaurus. For instance, the Eoraptor has the grasping, three-fingered hands typical of a theropod, designed to rake flesh from the dinosaurs' prey. The specimen measures about 40 inches from its nose to the tip of its tail and probably weighed around 25 pounds.
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