Editing Ungulate (section)

====Cetacean evolution====
{{See also|Evolution of cetaceans}}
[[File:Ambulocetus natans.jpg|thumb|Skeleton of ''[[Ambulocetus natans]]'', a stem whale]]
The traditional theory of cetacean evolution was that cetaceans were related to the [[Mesonychia|mesonychian]]. These animals had unusual triangular teeth very similar to those of primitive cetaceans.  This is why scientists long believed that cetaceans evolved from a form of mesonychian. Today, many scientists believe cetaceans evolved from the same stock that gave rise to hippopotamuses. This hypothesized ancestral group likely split into two branches around {{mya|54|million years ago}}.<ref name="Genomes" /> One branch would [[Evolution of cetaceans|evolve into cetaceans]], possibly beginning about {{mya|52|million years ago}} with the proto-whale ''[[Pakicetus]]'' and other early cetacean ancestors collectively known as [[Archaeoceti]], which eventually underwent [[aquatic adaptation]] into the completely aquatic [[cetacea]]ns.<ref name="Cetartiodactyla">{{cite journal |last=Boisserie |first=Jean-Renaud |author2=Lihoreau, F. |author3=Brunet, M. |date=February 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 |pmc=547867|bibcode = 2005PNAS..102.1537B |pmid= 15677331 |doi-access=free }}</ref> The other branch became the [[anthracotheriidae|anthracotheres]], a large family of four-legged beasts, the earliest of whom in the late [[Eocene]] would have resembled skinny hippopotamuses with comparatively small and narrow heads. All branches of the anthracotheres, except that which evolved into [[Hippopotamidae]], became extinct during the [[Pliocene]] without leaving any descendants.<ref name="ScienceNews">{{Cite web | title = Scientists find missing link between the dolphin, whale and its closest relative, the hippo | date = 2005-01-25 | access-date = 2007-06-18 | url = http://www.sciencenewsdaily.org/story-2806.html | work = Science News Daily | url-status = dead | archive-url = https://web.archive.org/web/20070304214747/http://www.sciencenewsdaily.org/story-2806.html | archive-date = 2007-03-04 }}</ref>

The family [[Raoellidae]] is said to be the closest artiodactyl family to the cetaceans.<ref>{{cite journal |last1=Thewissen |first1=J. G. M. |year=2007 |title=Whales originated from aquatic artiodactyls in the Eocene epoch of India |journal=Nature |volume=450 |issue=7173 |pages=1190–1194 |doi=10.1038/nature06343 |url= http://repository.ias.ac.in/4642/1/316.pdf|pmid=18097400 |last2=Cooper |first2=LN |last3=Clementz |first3=MT |last4=Bajpai |first4=S|author4-link=Sunil Bajpai |last5=Tiwari |first5=BN |bibcode=2007Natur.450.1190T|s2cid=4416444 }}</ref><ref>{{cite magazine
|url=http://www.sciam.com/article.cfm?id=closest-whale-cousin
|title=Closest Whale Cousin—A Fox-Size Deer? Researchers split on closest evolutionary kin to whales and dolphins
|first=JR
|last=Minkel 
|magazine=Scientific American
|date=2007-12-19}}</ref> Consequentially, new theories in cetacean evolution hypothesize that whales and their ancestors escaped predation, not competition, by slowly adapting to the ocean.<ref name=GuardianIndohyus>{{cite news |url=https://www.theguardian.com/science/2007/dec/19/whale.deer?gusrc=rss&feed=networkfront |title=Whales may be descended from a small deer-like animal  |access-date=2007-12-21 |author= Sample, Ian|date=December 19, 2007|work=[[Guardian Unlimited]] |location=London}}</ref><ref name=TheLoom>{{cite web |url=http://scienceblogs.com/loom/2007/12/19/whales_from_so_humble_a_beginn.php |title=The Loom : Whales: From So Humble A Beginning... |access-date=2007-12-21 |author=Zimmer, Carl |author-link=Carl Zimmer |date=December 19, 2007 |publisher=[[ScienceBlogs]] |archive-date=2007-12-21 |archive-url=https://web.archive.org/web/20071221103928/http://scienceblogs.com/loom/2007/12/19/whales_from_so_humble_a_beginn.php |url-status=dead }}</ref><ref name=PharyngulaIndohyus>{{cite web |url=http://scienceblogs.com/pharyngula/2007/12/indohyus.php |title=Pharyngula: Indohyus |access-date=2007-12-21 |author=Myers, P.Z. |author-link=PZ Myers |date=December 19, 2007 |work=[[Pharyngula (blog)|Pharyngula]] |publisher=[[ScienceBlogs]] |archive-date=2007-12-20 |archive-url=https://web.archive.org/web/20071220115757/http://scienceblogs.com/pharyngula/2007/12/indohyus.php |url-status=dead }}</ref>