Jurassic Fossil puts Mammals 100 million years older

Named Castorocauda lutrasimilis, Latin for beaver tail and similarity to the otter, this fossil has put the age of the aquatic Mammals back by another 100 million years. Earlier Paleontologists believed that the mammals appeared after the Jurassic era ended about some 65 million years ago. This fossil found in the Middle Jurassic Jiulongshan Formation in China in 2004 dates to 164 million years ago.

Researchers led by Qiang Ji at the Nanjing University in China and the Carnegie Museum of Natural History in Pittsburgh who named the animal have written that the mammal had a broad, flattened, partly scaly tail analogous to that of modern beavers, soft tissue webbing between the hind toes and had fur on the body.

Unlike the modern day beaver it did not eat just wood but also ate fish. The fossil suggests that it was about 50 centimeters long and research suggests that it weighed about 500gms.

In the article Published in the latest journal Science, Professor Ji and his team of researchers have said that the fossil indicated that some mammals occupied more diverse ecological place than had been suspected in the middle Jurassic age which was mostly dominated by the dinosaurs.

Thomas Martin of Senckenberg Research Institute in Frankfurt, Germany, said the find contradicted the popular view and pushed the "mammalian Conquest" of the aquatic life by more than 100 million years.

Though the mammal has similarities to some present day animals like the beaver and the platypus, it does not have any modern descendents. Its front paws were capable of burrowing, and the webbed hind feet enabled it to swim.

Castorocauda is probably the largest mammal of its time. Paleontologists believe that though the smaller mammals may have appeared as long ago as 200 million years larger mammals appeared only after the end of the Jurassic age.

The Jiulongshan Formation, which in the past has also has produced the fossils of dinosaurs, in the words of Professor Martin is just beginning to be exploited.