Genus: Eoraptor Sereno, Forster et al., 1993.
Type and only species: Eoraptor lunensis Sereno, Forster et al., 1993.
Time: earliest Carnian (Sereno, 2007).
Distribution: San Juan Province, Argentina.
Formation: Ischigualasto Formation.
Material: Nearly complete holotype skeleton; several unpublished referred specimens (Sereno, 2007).
Description: (Sereno, 2007) Bipedal. Forelimbs pentadactyl. Rudimentary palatal teeth on pterygoid. Lower jaw with intramandibular joint between splenial and angular elements, splenial process transversely concave. Three sacral ribs.
Comments: Eoraptor was one of the world's earliest dinosaurs. It was a two-legged meat-eater that lived between 230 and 225 million years ago, in what is now the northwestern region of Argentina. The type species is Eoraptor lunensis, which means 'dawn plunderer [from the Valley] of the Moon', denoting where it was originally discovered (Greek eos/ηως meaning 'dawn' or 'morning' and Latin lunensis meaning 'of the moon'). Different analyses have placed Eoraptor as either a basal saurischian outside the Sauropodomorpha + Theropoda clade, or as a basal theropod (Sereno, 2007). Paleontologists have noted that Eoraptor resembles the hypothetical common ancestor of all dinosaurs.
Eoraptor had a thin body that grew to about 1 meter (3 feet) in length, with an estimated weight of about 10 kilograms (22 pounds). It ran digitigrade, upright on its hind legs. Its fore limbs were only half the length of its hind limbs and it had five digits on each 'hand'. Three of those digits, the longest of the five, ended in large claws and were presumably used to handle prey. The fourth and fifth digits were probably too tiny to be of any use in hunting.
Eoraptor probably ate mostly small animals. It was a swift sprinter and, upon catching its prey, it would use claws and teeth to tear the prey apart. However, it had both carnivore-type and herbivore-type teeth, so it could possibly have been omnivorous.
The bones of this primitive dinosaur were first discovered in 1991, by University of Chicago paleontologist Paul Sereno, in the Ischigualasto Basin of Argentina. During the Late Triassic period, this was a river valley but is now desert badlands. Eoraptor was found in the Ischigualasto Formation, the same formation that yielded Herrerasaurus, a very early theropod. By 1993 it had been determined to be one of the basalmost dinosaurs. Eoraptor lacked the specialised features of any of the major groups of later dinosaurs. Unlike later theropods, it lacked a sliding joint at the articulation of the lower jaw with which to hold large prey. Furthermore, only some of its teeth were curved and saw-edged, unlike those in a later predator's mouth. The fact that it possessed five fully developed 'fingers' has led scientists to place Eoraptor as more basal than even Herrerasaurus.
Sereno, P. C. 2007. The phylogenetic relationships of early dinosaurs: a comparative report. Historical Biology 19 (1): 145-155.
Creditshttp://en.wikipedia.org/wiki/Eoraptor; edited CKT070718