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Species of the infraorder Cetacea A phylogenetic tree showing the relationships among cetacean families. [1]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]
The order Artiodactyla consists of 349 extant species belonging to 132 genera. This does not include hybrid species or extinct prehistoric species. Modern molecular studies indicate that the 132 genera can be grouped into 23 families; these families are grouped into named suborders and many are further grouped into named clades, and some of these families are subdivided into named subfamilies.
Comparison of even-toed ungulate and cetaceans genetic material has shown that the closest living relatives of whales and hippopotamuses is the paraphyletic group Artiodactyla. [7] [8] Dan Graur and Desmond Higgins were among the first to come to this conclusion, and included a paper published in 1994. [9]
The sperm whale or cachalot (Physeter macrocephalus) is the largest of the toothed whales and the largest toothed predator.It is the only living member of the genus Physeter and one of three extant species in the sperm whale family, along with the pygmy sperm whale and dwarf sperm whale of the genus Kogia.
The pygmy right whale shares several characteristics with the right whales, with the exception of having a dorsal fin. Also, pygmy right whales' heads are no more than one quarter the size of their bodies, whereas the right whales' heads are about one-third the size of their bodies. [11] The pygmy right whale is the only extant member of its ...
Dinosaurs show some of the most extreme variations in size of any land animal group, ranging from tiny hummingbirds, which can weigh as little as two grams, to the extinct titanosaurs, such as Argentinosaurus and Bruhathkayosaurus [1] which could weigh as much as 50–130 t (55–143 short tons).
Ambulocetus (Latin ambulare "to walk" + cetus "whale") is a genus of early amphibious cetacean [a] from the Kuldana Formation in Pakistan, roughly 48 or 47 million years ago during the Early Eocene . It contains one species , Ambulocetus natans (Latin natans "swimming"), known solely from a near-complete skeleton.
The largest known basilosaurid, Perucetus colossus, is believed to be even bigger, with a length of about 17–20 metres (56–66 ft) and possibly comparable to, if not larger than, the modern blue whale in terms of weight, [15] though other researchers argue that it was much lighter.