Scientists believe that dinosaurs evolved from "dinosauromorphs." Until recently, scientists believed that dinosaurs quickly replaced their ancestors 200 to 300 million years ago in the late Triassic. A new study published in Science suggests that dinosaurs may have lived alongside their ancestors for an extended period of time.

Fossils analyzed in New Mexico along side anatomical findings indicates that the transition from dinosauromorphs to their dinosaur descendents was gradual, occurring over 15 to 20 million years.

Dinsoauromorph fossils are uncommon, and until recently the Chanres Formation in Argentina was the only place they had been found. According to these fossils paleontologists concluded that dinosauromorphs had died out abruptly in the middle Triassic when dinosaurs first emerged.

Read more here: http://www.sciencemag.org/cgi/conten...t/317/5836/358