Dinosaurs' gradual rise to dominance

By Sid Perkins, 15:57 PM April 15, 2008

Fossil finds in the southwestern United States suggest that dinosaurs didn't quickly supplant the creatures they evolved from, as many paleontologists have assumed.

The first dinosaurs evolved from reptiles called dinosauromorphs about 235 million years ago. Until recently, scientists hadn't uncovered any dinosauromorph fossils from much after that time, fueling speculation that dinosaurs had swiftly eclipsed their ancestors, says Randall B. Irmis, a paleontologist at the University of Califo...

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