"We had only just re-opened the door on early dinosaurs and their world with the 1988 expedition. The Ischigualasto valley streched some 75 miles in length, and much of it we had yet to visit. The goals of this return expedition were to explore more remote regions of the valley, to search for bones of other early dinosaurs and dinosaurian precursors, and to attempt to date radiometrically the age of the beds.

Halfway through the season, Argentine team member Ricardo Martinez discovered a small 3 foot-long skeleton just coming to the surface. After detailed cleaning back in the laboratory, the hollowed skeleton of a new and very primitive predator emerged. We dubbed this dinosaur Eoraptor, or "dawn raptor," because its size and form differed little from what we estimate is the ancestral condition at the root of the dinosaur family tree. 

Eoraptor and the contemporary larger predator Herrerasaurus, however, show specializations that place them with other theropods. The dinosaurian radiation was underway, despite the fact that dinosaurs were outnumbered at this time by other kinds of reptiles. Volcanic ash deposits allowed us to determine an accurate radiometric age for the Ischigualsto beds nearest the dinosaurs--228 million years old, plus or minus 300,000 years. 

Returning to this area in 1991, we discovered a small skeleton belonging to a new species aptly named Eoraptor ("dawn raptor"). A primitive cousin of Herrerasaurus, Eoraptor measures only three feet from snout to tail tip. Ancient volcanic ash beds discovered near these early dinosaurs allowed Sereno's team to determine their age--228 million years old--and date the dawn of the dinosaur era. These discoveries shed light on the roots of the dinosaur family tree and on how and when dinosaurs came to dominate the land." - Paul Sereno