Cetaceans (aquatic mammals)

They are believed to have evolved from mammals and are classified under the suborder Archaeceti, which were mainly aquatic. Their hindlimbs were reduced, they had long snouts, and their forelimbs became paddle-like flippers or thoracic fins with hand and finger bones, so were adapted to the shallow coastal fringes of the seas Hyperion, 2003; Save the Whales, 2003).

During the Paleocene and Eocene consequences, a large amount of speciation took place, and natural pick favored adaptations to capture fast-moving fish, rather than the fresh- body of water molluscs their predecessors fed on (Hyperion, 2003). Their bodies were elongated, with nostrils on top of the snout, long palates, and heavy bones around the ears. They were control to warm waters, and could only make short dives.

In the Oligocene period from 38 to 25 million years ago, Archaeocetes were replace

During this time, the cetaceans became more aquatic: the body became more torpedo-shaped, a dorsal fin developed, which was later lost in rightwhale dolphins, the out-of-door nostrils moved backwards, the pelvic girdle was lost, and structures formed which helped seal the animals from water (Hyperion, 2003). Evolution favored an aquatic existence, and structures not compatible with such a life were lost while adaptations which aided such a lifestyle replaced them. By the late Oligocene, the dentition was change to one of homodonty. The skull was modified for scanning and diving, and echolocation was developed. The Squalodonts gave rise to the Eurhinodelphinidae - original dolphins - now called the Rhabdosteidae.

by at least four families: the Agorophilidae and Squalodentidae, which were twain primitive odontocetes, and the Aetiocetidae and Cetotheriidae, which were the early Mysticetes.

Geneti
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