Dinos, ancestors of crocs, fish lived together 220 mln years ago

Newly excavated fossils from the Hayden Quarry at Ghost Ranch, New Mexico has revealed that dinosaurs that their non-dinosaur ancestors lived side by side for tens of millions of years.

Washington, July 20 : Newly excavated fossils from the Hayden Quarry at Ghost Ranch, New Mexico has revealed that dinosaurs that their non-dinosaur ancestors lived side by side for tens of millions of years.

Palaeontologists from the University of California, Berkeley, the American Museum of Natural History and The Field Museum found both early dinosaurs and dinosaur precursors, not to mention bones of crocodile ancestors, fish and amphibians, all dating between 220 and 210 million years ago.

The team also discovered the leg bones (femurs) of the carnivorous Chindesaurus bryansmalli (SHIN dee SOAR us) and a close relative of the carnivorous Coelophysis (SEE low FIE sis), a well-known Triassic dinosaur.

Both walked on two legs, reminiscent of the much later Velociraptor depicted in the 1993 film "Jurassic Park" as a cunning pack hunter.

Researchers say the findings disprove the notion that dinosaurs rapidly replaced their supposedly outmoded predecessors.

"Up to now, palaeontologists have thought that dinosaur precursors disappeared long before the dinosaurs appeared, that their ancestors probably were out-competed and replaced by dinosaurs and didn't survive. Now, the evidence shows that they may have coexisted for 15 or 20 million years or more," said co-author Kevin Padian, professor of integrative biology at UC Berkeley and a curator in the campus's Museum of Paleontology.

According to primary authors Randall Irmis and Sterling Nesbitt, graduate students at UC Berkeley and New York's American Museum respectively, the new bones provide anatomical information that tells palaeontologists about the evolution of dinosaur precursors, their transition into true dinosaurs and how dinosaurs diversified.

"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," said Irmis.

Dinosaurs and many other animals, including mammals, lizards, crocodiles, turtles and frogs, arose in the Late Triassic, between 235 and 200 million years ago, but it was only in the Jurassic period 200-120 million years ago that dinosaurs dominated the planet and all their predecessors vanished.

Fossils of Late Triassic dinosaurs are thus rare, and until 2003, when a creature called Silesaurus (SIGH leh SOAR us) was discovered in Poland, no dinosaur precursors had been found from the Late Triassic either.he first dinosaur precursor found at the site was Dromomeron romeri (Dro MOE mer on RO mer eye), a creature related to a 235 million-year-old Argentinian middle Triassic precursor called Lagerpeton (LAG err peh TON). Dromomeron was between three and five feet long, and possibly bipedal.

The other precursor was an unnamed, quadrupedal, beaked grazer about three times the size of Dromomeron and similar to Silesaurus.

"Everyone thought that all the dinosaur precursors were little carnivorous, bipedal animals. This Silesaurus-like creature still has the gestalt of a dinosaur, but to find a quadrapedal, herbivorous one was kind of unexpected," said Irmis.

The study appears in the July 20 cover issue of Science.

ANI