- Aquatic adaptation
Several
animal groups have undergone aquatic adaptation, going from being purely terrestrial animals to living at least part of the time in water. The adaptations in early speciation tend to develop 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 the majority of their life in the water, coming ashore for mating. Finally, fully adapted animals may take to mating and birthing in water.Anapsid s"
Archelon ", was a genus giantCretaceous sea turtle ."
Mesosaurus " (and other mesosaurids) were one of the firstreptiles to secondarily return to the sea.Cetacea nsDuring the
Paleocene Epoch (about 55-65 million years ago), a group ofwolf -likeartiodactyl s related to "Pakicetus " began pursuing an amphibious lifestyle in rivers or shallow seas. They were the ancestors of modern whales.Diapsid sLiving at the same time as, but not closely related to, dinosaurs, the
mosasaur s andpliosaur s resembled crocodiles but were more strongly adapted to marine life. They became extinct within a few million years of the dinosaurs. Modern diapsids which have adapted to marine life include marineiguana s and marinecrocodile s.Euryapsid sThese marine reptiles had ancestors who moved back into the oceans, In the case of
ichthyosaur s adapting as fully as thedolphins they superficially resemble, even giving birth to live offspring instead of laying eggs, in other cases more to the extent of the seal, as withplesiosaur s andplacodont s.Human sSome people believe that part of
human evolution includes some aquatic adaptation, which has been said to explain human hairlessness, webbed digits, bipedal locomotion, and various other physiological changes. In addition, there have been numerous inventions of devices by humans to adapt to the aquatic environments.Pinniped sThe fossil records show that
phocid s existed 12 to 15 million years ago, andodobenid s about 14 million years ago. Their common ancestor must have existed even earlier than that.Polar Bear sAlthough still primarily a terrestrial animal, the polar bear shows the beginnings of aquatic adaptation to swimming (body fat, closable nostrils), diving, and thermoregulation. Distinctly polar bear fossils can be dated to about 100,000 years ago.
Sirenia nsThe ancestors of the
dugong andmanatee s first appeared in the fossil record about 45 to 50 million years ago in the Eocene.
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