Like the cetaceans, pinnepeds also evolved from a common terrestrial carnivore. They are found in mid-latitude and polar oceans. Pinnepeds cannot spend long periods of time under-water. Manatees and dugongs are tropical herbivores. They can inhabit fresh water as well as sea water.
Sea otters live in cold, coastal waters.
They are carnivores, usually feeding on benthic shellfish. There are relatively few species, but all are successful in the ocean. Several varieties of fish, reptiles, and mammals migrate long distances during their life cycles. For these animals, migration links regions that are appropriate for reproduction with regions of feeding for adults.