Humpback - dog tooth / nerve cell - Humpback - Dog Tooth / Nerve Cell (Vinyl) at Discogs

The aquatic lifestyle of cetaceans first began in the Indian subcontinent from even-toed ungulates 50 million years ago, over a period of at least 15 million years, however a jawbone discovered in Antarctica may reduce this to 5 million years. [3] Archaeoceti is an extinct parvorder of Cetacea containing ancient whales. The traditional theory of cetacean evolution, first proposed by Van Valen in 1966, [4] was that whales were related to the mesonychids , an extinct order of carnivorous ungulates (hoofed animals) that resembled wolves with hooves and were a sister group of the artiodactyls (even-toed ungulates). This theory arose due to similarities between the unusual triangular teeth of the mesonychids and those of early whales. However, molecular phylogeny data indicates that whales are very closely related to the artiodactyls, with hippopotamuses as their closest living relative. Because of this, cetaceans and hippopotamuses are placed in the same suborder , Whippomorpha . [5] Cetartiodactyla (formed from the words Cetacea and Artiodactyla) is a proposed name for an order containing both cetaceans and artiodactyls. However, the earliest anthracotheres , the ancestors of hippos, do not appear in the fossil record until the Middle Eocene, millions of years after Pakicetus , the first known whale ancestor, appeared during the Early Eocene, implying the two groups diverged well before the Eocene. Since molecular analysis identifies artiodactyls as being very closely related to cetaceans, mesonychids are probably an offshoot from Artiodactyla, and cetaceans did not derive directly from them, but possibly sharing a common ancestor. [6]

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