Whales and dolphins weren't the only mammals who changed their minds about life on land. The ocean also called out to the roly poly sea cow relative, Desmostylus, pictured here seizing the day. Though this animal is not the direct ancestor of modern sea cows, it is at least the grand-uncle of the Sirenia order. Fun fact: one of the closest relatives of the sea cow is the elephant. The two groups branched off from each other in the Eocene, only 50 million years ago.
Image by Dmitry Bogdanov.