Editing Whale (section)

===Evolution===
{{Main|Evolution of cetaceans}}
[[File:Basilosaurus cetoides (1).jpg|right|thumb|[[Basilosaurus]] skeleton]]

Whales are descendants of land-dwelling mammals of the [[artiodactyl]] [[order (biology)|order]] (even-toed ungulates). They are related to the ''[[Indohyus]]'', an extinct [[chevrotain]]-like ungulate, from which they split approximately 48 million years ago.{{sfn|Northeastern Ohio Universities|2007}}{{sfn|Dawkins|2004}} Primitive cetaceans, or [[archaeocetes]], first took to the sea approximately 49 million years ago and became fully aquatic 5–10 million years later. What defines an archaeocete is the presence of anatomical features exclusive to cetaceans, alongside other primitive features not found in modern cetaceans, such as visible legs or asymmetrical teeth.{{sfn|Berkeley}}{{sfn|Thewissen et al.|2007}}{{sfn|Fahlke et al.|2011}}{{sfn|Gatesy|1997}} Their features became adapted for living in the [[Sea|marine environment]]. Major anatomical changes included their hearing set-up that channeled vibrations from the jaw to the earbone (''[[Ambulocetus]]'' 49 [[Mya (unit)|mya]]), a [[streamline (fluid dynamics)|streamlined]] body and the growth of flukes on the tail (''[[Protocetus]]'' 43 mya), the migration of the nostrils toward the top of the [[cranium]] ([[Blowhole (anatomy)|blowholes]]), and the modification of the forelimbs into flippers (''[[Basilosaurus]]'' 35 mya), and the shrinking and eventual disappearance of the hind limbs (the first odontocetes and mysticetes 34 mya).{{sfn|Kenneth|2001}}{{sfn|Bebej et al.|2012}}{{sfn|Reidenberg|2012|p=508}}

Whale morphology shows several examples of [[convergent evolution]], the most obvious being the streamlined fish-like body shape.{{sfn|Lam|1999}} Other examples include the use of [[Animal echolocation|echolocation]] for hunting in low light conditions&nbsp;— which is the same hearing adaptation used by [[bat]]s&nbsp;— and, in the rorqual whales, jaw adaptations, similar to those found in [[pelican]]s, that enable engulfment feeding.{{sfn|Moskowitz|2011}}

Today, the closest living relatives of cetaceans are the [[hippopotamus]]es; these share a [[Semiaquatic|semi-aquatic]] ancestor that branched off from other artiodactyls some 60 mya.{{sfn|Gatesy|1997}} Around 40 mya, a common ancestor between the two branched off into cetacea and [[anthracotheres]]; nearly all anthracotheres became extinct at the end of the Pleistocene 2.5 mya, eventually leaving only one surviving lineage&nbsp;– the hippopotamus.{{sfn|Boisserie|Lihoreau|Brunet|2005}}

Whales split into two separate parvorders around 34 mya&nbsp;– the baleen whales (Mysticetes) and the toothed whales (Odontocetes).{{sfn|PBS ''Nature''|2012}}{{sfn|Houben et al.|2013|pp=341–344}}{{sfn|Steeman et al.|2009|pp=573–585}}