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Like other aquatic mammals, they do not represent a biological grouping. [26] The humpback whale is a fully aquatic marine mammal. Marine mammal adaptation to an aquatic lifestyle vary considerably between species. Both cetaceans and sirenians are fully aquatic and therefore are obligate ocean dwellers.
The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates (Artiodactyla) 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. [2] Cetaceans are fully aquatic mammals belonging to the order Artiodactyla and branched off from other artiodactyls around 50 mya.
The term "marine mammal" encompasses all mammals whose survival depends entirely or almost entirely on the oceans, which have also evolved several specialized aquatic traits. In addition to the above, several other mammals have a great dependency on the sea without having become so anatomically specialized, otherwise known as "quasi-marine ...
The aquatic ape hypothesis (AAH), also referred to as aquatic ape theory (AAT) or the waterside hypothesis of human evolution, postulates that the ancestors of modern humans took a divergent evolutionary pathway from the other great apes by becoming adapted to a more aquatic habitat. [1]
The evolution of the digestive system has formed a significant influence in mammal evolution. With the emergence of mammals, the digestive system was modified in a variety of ways depending on the animal's diet. For example, cats and most carnivores have simple large intestines, while the horse as a herbivore has a voluminous large intestine. [127]
The dugong (/ ˈ d (j) uː ɡ ɒ ŋ /; Dugong dugon) is a marine mammal.It is one of four living species of the order Sirenia, which also includes three species of manatees.It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow (Hydrodamalis gigas), was hunted to extinction in the 18th century.
Fossils have been found in marine strata. The nares are retracted and the orbits are raised like in other aquatic mammals. Levels of stable isotopes in their tooth enamel suggest an aquatic diet and environment (carbon and oxygen) and fresh or brackish water (strontium). Their spongy bone structure is similar to that of cetaceans.
Berta A (2012). "5. Diversity, Evolution, and Adaptation of Sirenians and Other Marine Mammals". Return to the Sea: The Life and Evolutionary Times of Marine Mammals. Berkeley: University of California Press. pp. 127– 149. ISBN 978-0-520-27057-2. Berta A, Sumich JL, Kovacs KK (2006). "5. Sirenian and Other Marine Mammals: Evolution and ...