US: Call it the eager beaver of Jurassic Park. With the tail of a beaver, teeth of an otter and lifestyle of a platypus, a furry creature with an early affinity for water may force scientists to drop the notion that mammals in the "Age of Dinosaurs" were cowering shrews with no real skills.
The newly found, 164-million-year-old fossil suggests its owner sported abundant hair, a broad and flattened tail, specialised molars for eating fish, and strong arms equipped for digging. These are signs that primitive mammals thrived in prehistoric pools at least 100 million years earlier than thought.
Zhe-Xi Luo, a curator of vertebrate palaeontology at the Carnegie Museum of Natural History in Pittsburgh and a co-author of the study, said the well-preserved fossil came as a "great surprise" to his team.
"We used to have this stereotypical impression of animals in the time of the dinosaurs: that they were all small, constrained by their size to eating invertebrates and insects," he said.
Researchers thought they were "good at a little bit of everything, but specialised in nothing".
The fossil find from China's Inner Mongolia region, reported in yesterday's issue of the journal Science, implies some forerunners of modern mammals possessed key adaptations that allowed them to invade a range of habitats well before the dinosaurs' demise. And although the weight of previously known mammal-like creatures from the period has been estimated at less than 57g (two ounces), Mr Luo's group put the newly discovered animal's weight at about 0.8kg (1.8 pounds) - making it "a giant among midgets".
The researchers found impressions of long hairs around the fossilised body and its leather-like scaly tail, as well as signs of carbonised underfurs. "Were it not for evolution, were it not for the formation of this creature in the past, you would have never conceived of such a combination," said Mr Luo.