Marine mammal Marine mammal Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They do not represent a distinct taxon or systematic grouping, but rather have a polyphyletic relation due to convergent evolution, as in they do not have an immediate common ancestor. They are also unified by their reliance on the marine environment for feeding. Marine mammal adaptation to an aquatic lifestyle varies considerably between species. Both cetaceans and sirenians are fully aquatic and therefore are obligate water dwellers. Seals
Mammal speed to a burrowing mammal, but semi-fossorial mammals have [[cursorial]] legs. The front paws are broad and have strong claws to help in loosening dirt while excavating burrows, and the back paws have webbing, as well as claws, which aids in throwing loosened dirt backwards. Most have large incisors to prevent dirt from flying into their mouth. [[File:Living-on-the-Edge-Settlement-Patterns-by-the-Symbiotic-Barnacle-Xenobalanus-globicipitis-on-Small-pone.0127367.s001.ogv|thumb|A pod of [[short-beaked common dolphin]]s swimming]] Fully aquatic mammals, the cetaceans and [[sirenia]]ns, have lost their legs and have a tail fin to propel themselves through the water. Flipper movement is continuous. Whales swim by moving their tail fin and lower body