All marine mammals have terrestrial ancestor and they have lost or changed the use of their legs to a greater or lesser. Degree. Mammals returned to the sea by several different evolutionary paths. The, living seals sea lions and fur seals are. Descended from early carnivores and probably arrived by, two routes diverging in the early Miocene about 20, million years. Ago. One subgroup the Otarioids, who had bear-like ancestors and evolved mainly in the, North Pacific led on the one hand. To the fur seals and sea lions (Otariids) and on the other hand to the walruses (Odobenids). The former have small external. Ears and the, males external testes which the walruses do not (their most obvious special feature is a webbed tail); all. Have hind flippers that can be turned forward so walking is possible; no fur on their palms and soles; and a light colored. Skin under their fur. These and many other anatomical features distinguish the subgroup as a whole from the other major. Subgroup the, phocoids.
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