Fossil may change evolutionary timeline

May 18, 2011 at 8:21 PM
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SEATTLE, May 18 (UPI) -- A fossil in China from a 247-million-year-old creature shows the family trees of birds and crocodiles split earlier than previously thought, researchers say.

The fossil specimen of Xilousuchus sapingensis has been classified as an archosaur, characterized by a skull with long, narrow snouts and teeth set in sockets, which includes dinosaurs as well as crocodiles and birds.

The family trees of birds and crocodiles were still joined in the Triassic period -- but the finding of X. sapingensis places it firmly in the crocodile family tree, and its age shows an earlier split from the bird family tree than paleontologists had believed, a University of Washington release said Wednesday.

The Triassic period was 251 million to 199 million years ago.

"We're marching closer and closer to the Permian-Triassic boundary with the origin of archosaurs," University of Washington paleontologist Sterling Nesbitt said.

The creature lived just a short geological time after the largest mass extinction in Earth's history, 252 million years ago at the end of the Permian period, when as much as 95 percent of marine life and 70 percent of land creatures perished.

There has been debate among paleontologists about whether archosaurs existed before the Permian period and survived the extinction event.

"Archosaurs might have survived the extinction or they might have been a product of the recovery from the extinction," Nesbitt said.

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