Whales started small

The ancestors of whales, some of which are the largest creatures ever to evolve, were probably mammals no larger than a fox. New fossils of Indohyus, a genus previously known only from some teeth and a jawbone fragment, led researchers to identify these deerlike creatures as the closest known relatives of primitive whales.

Certain features of the animals’ skulls and earbones match those of whales and their close relatives but no other mammals, says Hans Thewissen, a paleontologist at the Northeastern Ohio Universities College of Medicine in Rootstown. Indohyus’ bones are thicker than average for an animal its size, a buoyancy-stifling characteristic that would have enabled it to live partly underwater. Indohyus lived about 48 million years ago in southern Asia, Thewissen and his colleagues report in the Dec. 20/27 Nature.