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Marine mammal adaptation to an aquatic lifestyle vary considerably between species. Both cetaceans and sirenians are fully aquatic and therefore are obligate ocean dwellers. Pinnipeds are semiaquatic; they spend the majority of their time in the water, but need to return to land for important activities such as mating, breeding and molting.
Marine mammal adaptation to an aquatic lifestyle varies considerably between species. Both cetaceans and sirenians are fully aquatic and therefore are obligate water dwellers. Pinnipeds are semiaquatic; they spend the majority of their time in the water but need to return to land for important activities such as mating, breeding and molting.
Secondary aquatic adaptations tend to develop in early speciation as the animal ventures into water in order to find available food. As successive generations spend more time in the water, natural selection causes the acquisition of more adaptations. Animals of later generations may spend most their life in the water, coming ashore for mating.
Aquatic animals generally conduct gas exchange in water by extracting dissolved oxygen via specialised respiratory organs called gills, through the skin or across enteral mucosae, although some are evolved from terrestrial ancestors that re-adapted to aquatic environments (e.g. marine reptiles and marine mammals), in which case they actually ...
Marine mammals adaptation to deep and long duration breath-hold diving involves more efficient use of lungs that are proportionately smaller than those of terrestrial animals of similar size. The adaptations to the lungs allow more efficient extraction of oxygen from inhaled air, and a higher exchange rate of air of up to 90% of each breath.
Marine mammal rehabilitation programs have been underway and regulated in the United States for more than 40 years. In 1973, injured and distressed manatees were rescued or aided in Florida. Eventually, the program was formalized into the Manatee Rescue, Rehabilitation, and Release Program managed by the US Fish and Wildlife Service.
Dolphins (aquatic mammals) and ichthyosaurs (extinct marine reptiles) share a number of unique adaptations for fully aquatic lifestyle and are frequently used as extreme examples of convergent evolution. Modern cetaceans have internal, rudimentary hind limbs, such as reduced femurs, fibulas, and tibias, and a pelvic girdle.
The whale ear has specific adaptations to the marine environment. In humans, the middle ear works as an impedance equalizer between the outside air's low impedance and the cochlear fluid's high impedance. In whales, and other marine mammals, there is no great difference between the outer and inner environments.