Scientists in China have discovered that some of our earliest mammalian ancestors managed to rise above the mouse-like creatures that scurried beneath the dinosaurs in pursuit of bugs.
Paleontologists from Nanjing University and the Carnegie Museum of Natural History say they have found the 165 million-year-old fossil remains of a 20-inch-long semi-aquatic carnivore that looks like a cross between a beaver and a river otter.
The fossil preserved impressions of fur and a flat, partly scaled tail, as well as webbing between the hind toes. Dubbed Castorocauda lutrasimilis ("beaver-tailed, otter-like animal") the animal also had a long, narrow skull packed with seal-like teeth adapted for eating fish and insects. Its front feet appear suited for burrowing and paddling in shallow lakes.
Writing in today's issue of the journal Science, Nanjing University's Qiang Ji and his colleagues said the 1.8-pound animal is the largest-known mammal from the Jurassic period.
"We know it was a swimmer," said co-author Zhe-Xi Luo, a vertebrate paleontologist at the Carnegie Museum of Natural History in Pittsburgh.
The researchers say the fossil shows that mammals developed specialized body forms, fur and ecological roles much earlier than previously thought - 100 million years before the extinction of the dinosaurs opened even richer opportunities for them.