for National Geographic News
A new species of dinosaur ancestor is among a fossil trove recently uncovered in New Mexico that suggests the rise of the dinosaurs was a gradual process.
The find counters the theory that dinos came to dominate the landscape suddenly as the result of an evolutionary "lucky break."
Until now, fossils of dinosaur precursors had been found only in rocks more than 230 million years old. The first true dinosaurs were found in much younger deposits.
(Related: "T. Rex's Oldest Ancestor Discovered in China" [February 8, 2006].)
This lack of overlap led many experts to conclude that dinosaurs had burst onto the scene after intense competition or a dramatic extinction event wiped out their predecessors.
But the latest bounty of bones from late Triassic rocks—between 210 million and 220 million years old—includes fossils of several different kinds of dinosaur relatives alongside those of early true dinosaurs.
The mixed assembly led the paleontologists who found the fossils to conclude that the two groups lived side-by-side for 15 million to 20 million years.
"For the first time anywhere in the world we found a variety of these dinosaur precursors with true dinosaurs," said Randall Irmis, a paleontologist at the University of California, Berkeley, who helped lead the dig.
"That suggests that the rise of the dinosaurs was gradual, rather than sudden."
Irmis and colleagues describe the newfound fossils in tomorrow's issue of the journal Science.
Hikers first noticed fossil bones a few years ago at the base of a hillside on Ghost Ranch in Abiquiu—once frequented by painter Georgia O'Keefe—which lies about 40 miles (64 kilometers) north of Española (see a map of New Mexico).
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