New fossil overturns previous ideas of Jurassic mammals

Friday, February 24, 2006

WASHINGTON -- This furry, beaver-like animal is turning the scientific world upside down.

The discovery shows that mammals were a bigger deal, ecologically speaking, in the time of dinosaurs than previously thought, said Zhe-Xi Luo, curator of vertebrate paleontology at Carnegie Museum of Natural History in Pittsburgh.

For over a century, the stereotype of mammals living in that era has been of tiny, shrew-like creatures scurrying about in the underbrush trying to avoid the giant creatures that dominated the planet, Luo commented.

But the finding suggests they weren't so wimpy after all. It is the earliest swimming mammal to have been found and was the most primitive mammal to be preserved with fur, which is important to helping keep a constant body temperature.

The new animal is not related to modern beavers or otters but has features similar to them. Thus the researchers named it Castorocauda lutrasimilis. Castoro from the Latin for beaver, cauda for tail, lutra for river otter and similis meaning similar.

It had a flat, scaly tail like a beaver, vertebra like an otter and teeth like a seal for swimming in lakes and eating fish. It's about 164 million years old.

It weighed between 1.1 and 1.7 pounds, about the size of a small female platypus.

The team, led by Qiang Ji of the Chinese Academy of Geological Sciences in Beijing, discovered the remains in the Inner Mongolia region of China. They report their findings in today's issue of the journal Science.

It's the first evidence that some ancient mammals were semi-aquatic, indicating a greater diversification than previously thought, the researchers said.

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