Friday, July 20, 2007
Jul. 20, 2007 (Xinhua News Agency delivered by Newstex) -- Rise of dinosaurs in Late Triassic more gradual than once thought
WASHINGTON, July 20 (Xinhua) -- The dinosaurs' rise to dominance was a gradual ascent rather than a sudden takeover, according to a new research published Friday in the journal Science.
Dinosaurs had become the most common land animals by the Jurassic period, about 200 to 150 million years ago, but the dinosaur fossil record leading up to that period is relatively sparse, making it difficult to tell how the dinosaurs achieved their success.
Some researchers have proposed that the true dinosaurs replaced their predecessors, a group of dinosaur-like reptiles called the ' dinosauromorphs,' relatively quickly.
According to this 'lucky break' scenario, dinosaurs would have either outcompeted their earlier relatives for resources or moved into their ecological niche after some sort of extinction event depleted the dinosauromorph numbers.
Randall Irmis from University of California, Berkeley and collaborators now describe a collection of fossils from New Mexico that challenges the lucky break scenario -- at least for the Triassic period, which preceded the Jurassic -- and suggest that dinosaurs and dinosauromorphs coexisted for about 15 to 20 million years toward the end of the Triassic.
The fossil assemblage contains a variety of dinosaurs, including carnivorous theropods (the group to which T. rex belongs) , early dinosauromorphs including a newly identified species called Dromomeron romeri, and other fishes, amphibians and crocodile-relatives.
'Finding dinosaur precursors, or basal dinosauromorphs, together with dinosaurs tells us something about the pace of changeover,' Irmis said. 'If there was any competition between the precursors and dinosaurs, then it was a very prolonged competition. '
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