Editing Dolphin (section)

==Evolution{{anchor|Evolution and anatomy}}==
{{Main|Evolution of cetaceans}}
[[File:Ichthyosaur vs dolphin.svg|thumb|Dolphins display [[convergent evolution]] with fish and [[Ichthyosaur|aquatic reptiles]].]]

Dolphins 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.<ref name=science_news>{{cite web |url=https://www.sciencedaily.com/releases/2007/12/071220220241.htm |title=Whales Descended From Tiny Deer-like Ancestors |access-date=December 21, 2007 |author=Northeastern Ohio Universities Colleges of Medicine and Pharmacy |website=ScienceDaily}}</ref><ref name="Ancestors_Tale">{{cite book|last=Dawkins|first=Richard|title=The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution|url={{google books |plainurl=y |id=wojUDAAAQBAJ}}|date=September 6, 2016|publisher=Houghton Mifflin Harcourt|isbn=978-0-547-52512-9}}</ref>

The primitive cetaceans, or [[archaeocetes]], first took to the sea approximately 49 million years ago and became fully aquatic by 5–10&nbsp;million years later.<ref name=radiations>{{cite journal |last=[[Hans Thewissen|Thewissen]]|first=J. G. M. |author2=Williams, E. M. |title=THE EARLY RADIATIONS OF CETACEA (MAMMALIA): Evolutionary Pattern and Developmental Correlations |journal=Annual Review of Ecology and Systematics |date=November 1, 2002 |volume=33 |issue=1 |pages=73–90 |doi=10.1146/annurev.ecolsys.33.020602.095426|bibcode=2002AnRES..33...73T }}</ref>

[[Archaeoceti]] is a parvorder comprising ancient whales. These ancient whales are the predecessors of modern whales, stretching back to their first ancestor that spent their lives near (rarely in) the water. Likewise, the archaeocetes can be anywhere from near fully terrestrial, to semi-aquatic to fully aquatic, but what defines an archaeocete is the presence of visible legs or asymmetrical teeth.<ref>{{cite web |url=http://www.ucmp.berkeley.edu/mammal/cetacea/cetacean.html |title=Introduction to Cetacea: Archaeocetes: The Oldest Whales |publisher=University of Berkeley |access-date=July 25, 2015}}</ref><ref>{{cite journal |last1=Thewissen|first1=J. G. M. |last2=Cooper |first2=L. N. |last3=Clementz |first3=M. T. |last4=Bajpai |first4=S. |last5=Tiwari |first5=B. N. |title=Whales originated from aquatic artiodactyls in the Eocene epoch of India |year=2007 |journal=Nature |volume=450 |issue=7173 |pages=1190–1194 |url=http://repository.ias.ac.in/4642/1/316.pdf |doi=10.1038/nature06343 |pmid=18097400 |bibcode=2007Natur.450.1190T|s2cid=4416444 |author1-link=Hans Thewissen }}</ref><ref>{{cite journal |last1=Fahlke |first1=Julia M. |last2=Gingerich |first2=Philip D. |last3=Welsh |first3=Robert C. |last4=Wood |first4=Aaron R. |title=Cranial asymmetry in Eocene archaeocete whales and the evolution of directional hearing in water |year=2011 |journal=PNAS |volume=108 |issue=35 |pages=14545–14548 |doi=10.1073/pnas.1108927108 |pmid=21873217 |bibcode=2011PNAS..10814545F |pmc=3167538|doi-access=free }}</ref><ref>{{cite news |url=http://news.bbc.co.uk/1/hi/sci/tech/1974869.stm |title=More DNA Support for a Cetacea/Hippopotamidae Clade: The Blood-Clotting Protein Gene y-Fibrinogen |work=BBC News|date=May 8, 2002 |access-date=August 20, 2006}}</ref> Their features became adapted for living in the [[Sea|marine environment]]. Major anatomical changes include the hearing set-up that channeled vibrations from the jaw to the earbone which occurred with ''[[Ambulocetus]]'' 49 million years ago, a [[streamline (fluid dynamics)|streamlining]] of the body and the growth of flukes on the tail which occurred around 43 million years ago with ''[[Protocetus]]'', the migration of the nasal openings toward the top of the [[cranium]] and the modification of the forelimbs into flippers which occurred with ''[[Basilosaurus]]'' 35 million years ago, and the shrinking and eventual disappearance of the hind limbs which took place with the first odontocetes and mysticetes 34&nbsp;million years ago.<ref>{{cite episode |series=[[Walking with Prehistoric Beasts]] |title=New Dawn |network=Discovery Channel |airdate=2002 }}</ref><ref>{{cite web |url=http://courses.washington.edu/biol354/Rose_Science_WHIPPO.pdf |title=The Ancestry of Whales |author=Rose, Kenneth D. |publisher=University of Washington |volume=239 |year=2001 |pages=2216–2217}}</ref><ref>{{cite journal |last1=Bebej |first1=R. M. |last2=ul-Haq |first2=M. |last3=Zalmout |first3=I. S. |last4=Gingerich |first4=P. D. |title=Morphology and Function of the Vertebral Column in ''Remingtonocetus domandaensis'' (Mammalia, cetacea) from the Middle Eocene Domanda Formation of Pakistan |journal=Journal of Mammalian Evolution |date=June 2012 |volume=19 |issue=2 |doi=10.1007/S10914-011-9184-8 |pages=77–104|s2cid=17810850 }}</ref> The modern dolphin [[skeleton]] has two small, rod-shaped pelvic bones thought to be [[vestigial]] hind limbs. In October 2006, an unusual bottlenose dolphin was captured in Japan; it had small [[fin]]s on each side of its genital slit, which scientists believe to be an unusually pronounced development of these vestigial hind limbs.<ref>{{cite news
|url=http://news.nationalgeographic.com/news/2006/11/061106-dolphin-legs.html |archive-url=https://web.archive.org/web/20061113052710/http://news.nationalgeographic.com/news/2006/11/061106-dolphin-legs.html |url-status=dead |archive-date=November 13, 2006 |title=Dolphin With Four Fins May Prove Terrestrial Origins |work=National Geographic |last=Lovett |first=Richard A. |date=November 8, 2006 |access-date=July 27, 2012}}</ref>

Today, the closest living relatives of cetaceans are the [[hippopotamus]]es; these share a semi-aquatic ancestor that branched off from other artiodactyls some 60 million years ago.<ref>{{cite web |url=http://mbe.oxfordjournals.org/content/14/5/537.full.pdf |archive-url=https://web.archive.org/web/20151015214719/http://mbe.oxfordjournals.org/content/14/5/537.full.pdf |url-status=dead |archive-date=October 15, 2015 |title=whales' closest relative |author=Gatesy, John |publisher=University of Arizona |date=February 3, 1997 |access-date=August 29, 2015}}</ref> Around 40 million years ago, a common ancestor between the two branched off into cetacea and [[anthracotheres]]; anthracotheres became extinct at the end of the Pleistocene two-and-a-half million years ago, eventually leaving only one surviving lineage: the two species of hippo.<ref>{{cite web |url=http://evolution.berkeley.edu/evolibrary/article/evograms_03 |title=The evolution of whales |publisher=University of Berkeley |access-date=August 29, 2015}}</ref><ref>{{cite journal |author1=Boisserie, Jean-Renaud |author2=Lihoreau, Fabrice |author3=Brunet, Michel |year=2005 |title=The position of Hippopotamidae within Cetartiodactyla |journal=Proceedings of the National Academy of Sciences |volume=102 |issue=5 |pages=1537–1541 |doi=10.1073/pnas.0409518102 |pmid=15677331 |bibcode=2005PNAS..102.1537B |pmc=547867|doi-access=free }}</ref>