The most primitive dinosaur ever found is Eoraptor. It may be one of the earliest dinosaurs that ever existed. The name Eoraptor means “dawn thief,” “early plunderer,” or “dawn raptor.” Eoraptor was closely related to another dinosaur of its time called Herrerasaurus.

Where and when Eoraptor lived

Eoraptor lived about 231 to 223 million years ago during the period of the Earth's history known as the Triassic. Eoraptor fossils, or remains, have been discovered in Argentina in South America. The environment in which Eoraptor lived during the Triassic period was tropical. The area was a lowland coastal plain with many rivers and lakes and heavy rainfall. Huge, fossilized tree trunks more than 130 feet (40 meters) tall give an example of the rich plant life present at that time. Fossil remains of other plant life, such as ferns and horsetails, have also been found in Eoraptor territory.

Physical features

Eoraptor was considerably smaller than most of the later dinosaurs. It grew to an average of about 3 feet (1 meter) in length and weighed about 22 pounds (10 kilograms). Eoraptor stood and walked on its two back legs and had relatively short front legs. It had five fingers on each front foot, but only three grew to a substantial length. Its front feet also were armed with long claws. Eoraptor had different types of razor-sharp teeth. Its top teeth were serrated like a saw and curved like those of other meat-eating dinosaurs. The bottom teeth were similar to those of the plant-eating dinosaurs.

Behavior

Eoraptor was a meat-eater. It preyed on small plant-eating dinosaurs as well as mammal-like reptiles that were plentiful at the time. The long, powerful back legs of Eoraptor may have given it an advantage over its competitors. Scientists also believe that Eoraptor, like other meat-eating dinosaurs, may have been a scavenger, feeding on dead animals.