What is Evolution of cetaceans?
[[File:Evolutionary pathway.jpg|thumb|right|280px|A phylogeny showing the relationships among cetacean families.<ref name=radiations>{{cite journal| last=Thewissen J.G M. & Williams E.M.| title=The early radiations of Cetacea (Mammalia): evolutionary pattern and developmental correlations| journal=Annual Review of Ecology and Systematics| date=2002| volume=33| issue=1| pages=73–90| doi=10.1146/annurev.ecolsys.33.020602.095426}}</ref> ]] The [[Cetacean]]s ([[whale]]s, [[dolphin]]s and [[porpoise]]s) are [[mammal]]ian [[Ocean|marine]] descendants of land [[mammal]]s. Their terrestrial origins are indicated by: * Their need to breathe air from the surface; * The bones of their fins, which resemble the limbs of land mammals * The vertical movement of their [[Vertebral column|spines]], characteristic more of a running mammal than of the horizontal movement of fish. The question of how land animals evolved into ocean-going [[leviathan]]s was a mystery until recent discoveries in [[Pakistan]] revealed several stages in the transition of cetaceans from land to sea. == DNA sequence analysis == After many years when palaeontologists thought whales had evolved from [[mesonychid]]s, [[DNA]] [[sequence analysis]] showed the closest relationship was with [[artiodactyl]]s, the [[even-toed ungulate]]s. A new [[clade]] was created to include Cetacea and their nearest relatives, the [[hippopotamus]] family. This clade is called the '''Cetartiodactyla'''. == Fossil record == {{see|Archaeoceti}} [[File:Raoellids&cetaceans.jpg|thumb|right|280px|Possible relationships between cetaceans and other ungulate groups.<ref name=radiations/> <ref name=indohyus>{{cite journal| last=Thewissen J.G.M. |display-authors = etal| title=Whales originated from aquatic artiodactyls in the Eocene epoch of India| journal=Nature|date= 2007| volume=450| issue=7173| pages=1190–1194| doi=10.1038/nature06343| pmid=18097400| bibcode=2007Natur.450.1190T|s2cid = 4416444}}</ref>]] [[File:Indohyus BW.jpg|thumb|right|220px|Reconstruction of ''[[Indohyus]]'']] H