What is the Evolutionary History of Cetaceans?
Cetaceans, derived from the Latin word for whale, “cetus,” is the mammalian order which includes whales, dolphins and porpoises. Cetaceans are one of four mammal groups adapted to aquatic life, the others being the sirenians (dugongs and manatees), pinnipeds (seals and walruses), and an aquatic subfamily of mustelids, the otters. Like other aquatic mammals, the cetaceans evolved from terrestrial ancestors. For many years, it was a mystery how the cetaceans evolved to be what they are today. This lasted until the discovery of a group of terrestrial proto-whales, the pakicetids, in Pakistan in 1983. Pakicetids are the earliest known cetaceans, living during the early Eocene, about 53 milion years ago. Their fossils were dug up in an area of Pakistan that was coastal to the ancient Tethys Sea, a body of water connected to the World Ocean and most directly analogous to the Indian Ocean of today. Pakicetids are considered cetaceans because of three telltale features that only whales have: a
