Dinosaurs Coexisted With Ancestors

June 19, 2007 — Dinosaurs shared the Earth for millions of years with the species that were their ancestors, a new study concludes.

Dinosaurs arose in the Late Triassic, between 235 million and 200 million years ago, and came to dominate the planet in the Jurassic, 200 million to 120 million years ago.

Scientists had thought the dinosaurs rapidly replaced their ancestor species. Indeed, until 2003, when a creature called Silesaurus was discovered in Poland, no dinosaur precursors had been found from the Late Triassic.

Now, researchers report in the journal Science they have evidence from northern New Mexico that dinosaurs and their precursor species coexisted for tens of millions of years.

"Finding dinosaur precursors, or basal dinosauromorphs, together with dinosaurs tells us something about the pace of changeover. If there was any competition between the precursors and dinosaurs, then it was a very prolonged competition," Randall Irmis, a graduate student at the University of California, Berkeley and co-author of the report, said in a statement.

The team reported finding 1,300 fossil specimens, including several complete bones, at Hayden Quarry at Ghost Ranch, an area made famous through the paintings of Georgia O'Keefe.