Fossils shed new light on mammals

It may not have been the friendliest place for small furry creatures, but three newly identified squirrellike mammals thrived in the trees during the Jurassic Period, with dinosaurs walking below and flying reptiles soaring above.

Scientists announced on Wednesday the discovery in China of fossils belonging to the three creatures in a find that sheds light on a poorly understood collection of ancient mammals, and indicates that mammals as a group appeared earlier than some experts thought.

The three species come from a group called haramiyids that previously had been known only from isolated teeth and fragmented jaws. Scientists had not even been sure they were mammals at all.