Named Peregocetus pacificus, the whale species was dated to about 42.6 million years ago, during the middle Eocene epoch. Measuring 4 m (13 ft) long, its four legs, tail and snout make it look more like an otter than a whale.
The creature was clearly just as comfortable on dry land as it was in the water. The team discovered tiny hooves on the tips of its toes – a holdover from its land-dwelling ancestors, which also gave rise to animals like camels and pigs. But they also found clues that indicated those toes were webbed, helping Peregocetus swim. The structures of the vertebrae in its tail, similar to those in beavers and otters, also suggested that its tail played a key role in swimming.