26 Feb 2006

Jurassic Beaver

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The discovery of a new fossil in China, Castorocauda lutrasimilis, demonstrates that mammals appeared early, and in larger forms, than previously believed, living at the same time as dinosaurs.

The San Francisco Chronicle story reports:

The remarkable fossil bones of a fur-covered, swimming mammal that lived in the age of the dinosaurs 164 million years ago have been discovered in China, raising a wave of excitement among scientists whose timetable for mammalian evolution has just been pushed back by 100 million years.

The animal appears to have been more than a foot long and weighed nearly 2 pounds, with a tail remarkably like a beaver and seal-like teeth clearly adapted for catching and eating fish, its discoverers say…

..The furry mammal was found in a rich fossil bed in Inner Mongolia’s Ningcheng county, about 160 miles northeast of Beijing. Its nearly complete skeleton was extracted from a rock layer along with the bones of small, two-legged meat-eating dinosaurs, primitive winged reptiles and the abundant remains of long-extinct crustaceans.

The rocks encasing the fossil skeleton bore the clear imprint of the dense hairs that had covered its body when it died in the mud and the horny scales that covered its flattened tail, the scientists said. They named their animal Castorocauda lutrasimilis and said it must have resembled a modern river otter or the “duck-billed” platypus of Australia.

William Clemens, professor emeritus at UC Berkeley and a former director of the Museum of Paleontology there, said the discovery provides “really good evidence” that the animal was both a swimmer and a fish-eater.

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