A prehistoric whale, Rodhocetus was an aquatic mammal that lived in Eocene times. It still had four limbs, but its hindlimbs were...Read More >>A prehistoric whale, Rodhocetus was an aquatic mammal that lived in Eocene times. It still had four limbs, but its hindlimbs were paddle-like, to help propel it through the water. Three mammal groups are water-dwelling animals: the cetaceans (whales, dolphins and porpoises), the sirenians (manatees and dugongs) and the pinnipeds (seals, sea lions and walruses). Quite independently, animals from each of these groups evolved bodies designed for survival in the water. Other mammals, for example otters, beavers or hippos, spend a great deal of time in the water, but they also live on land, so their bodies are not so fundamentally altered.
Whales and dolphins
PakicetusCetaceans are the most specialized marine animals: they have fins and tails just like fish, but also flippers for steering. They would die if stranded out of water. It is difficult to imagine that the ancestors of whales once lived on land, but they did.
Whales are related to the even-toed ungulates, hoofed land animals. They share a common ancestor with the hippos.
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