Editing Hippopotamus (section)

===Evolution===
[[File:Evolutionary relationships among laurasiatherian mammals as used in molecular evolution analyses.jpg|thumb|Evolutionary relationships among hippo and Cetacea (whales, dolphins)<ref name="TsagkogeorgaMcGowen2015">{{cite journal |last1=Tsagkogeorga |first1=G. |last2=McGowen |first2=M. R. |last3=Davies |first3=K. T. J.|last4=Jarman |first4=S. |last5=Polanowski |first5=A. |last6=Bertelsen |first6=M. F. |last7=Rossiter |first7=S. J. |title=A phylogenomic analysis of the role and timing of molecular adaptation in the aquatic transition of cetartiodactyl mammals |journal=Royal Society Open Science |volume=2 |issue=9 |year=2015 |page=150156 |doi=10.1098/rsos.150156 |pmid=26473040 |pmc=4593674 |bibcode=2015RSOS....250156T}}</ref>]]
Until 1909, [[natural history|naturalists]] classified hippos together with pigs based on [[molar (tooth)|molar]] patterns. Several lines of evidence, first from blood proteins, then from [[molecular systematics]],<ref name=Genomes/> [[DNA]]<ref name=DNA>{{Cite journal |title=More DNA support for a Cetacea/Hippopotamidae clade: the blood-clotting protein gene gamma-fibrinogen |author=Gatesy, J. |journal=[[Molecular Biology and Evolution]] |date=1997 |volume=14 |pages=537–543 |pmid=9159931 |issue=5 |doi=10.1093/oxfordjournals.molbev.a025790 |doi-access=free}}</ref><ref name=Nature2009>{{Cite journal |title=Hippopotamus and whale phylogeny |author1=Geisler, J. H. |author2=Theodor, J. M. |journal=[[Nature (journal)|Nature]] |year=2009 |pmid=19295550 |volume=458 |doi=10.1038/nature07776 |bibcode=2009Natur.458....1G |issue=7236 |pages=E1–E4; discussion E5 |s2cid=4320261}}</ref> and the [[fossil record]], show their closest living relatives are [[cetacean]]s ([[whale]]s, [[dolphin]]s, and [[porpoise]]s).<ref name=ScienceNews>{{cite web |first=R. |last=Sanders |title=Scientists find missing link between the dolphin, whale and its closest relative, the hippo |date=2005 |archive-url= https://web.archive.org/web/20150226060713/http://www.innovations-report.com//html/reports/life-sciences/report-39309.html |archive-date= 26 February 2015 |url-status=live |access-date=8 January 2011 |url=http://www.innovations-report.com/html/reports/life_sciences/report-39309.html |work=Science News Daily}}</ref><ref name=Cetartiodactyla/> The common ancestor of hippos and whales branched off from [[Ruminantia]] and the rest of the even-toed ungulates; the cetacean and hippo lineages split soon afterwards.<ref name="DNA"/><ref name=Cetartiodactyla>{{cite journal |author1=Boisserie, J.-R. |author2=Lihoreau, F. |author3=Brunet, M. |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 |pmc=547867 |bibcode=2005PNAS..102.1537B |doi-access=free}}</ref>

{{Cetartiodactyla Cladogram}}
[[File:Anthracotherium magnum.jpg|thumb|right|''[[Anthracotherium]] magnum'' from the Oligocene of Europe]]
The most recent theory of the origins of Hippopotamidae suggests hippos and whales shared a common semiaquatic ancestor that branched off from other artiodactyls around {{mya|60|million years ago}}.<ref name=DNA/><ref name=ScienceNews/> This hypothesised ancestral group likely split into two branches again around {{mya|54|million years ago}}.<ref name=Genomes>{{Cite journal |title=Analyses of mitochondrial genomes strongly support a hippopotamus-whale clade |volume=265 |issue=1412 |year=1998 |journal=[[Proceedings of the Royal Society]] |pmid=9881471 |author1=Ursing, B. M. |author2=Arnason U. |pmc=1689531 |doi=10.1098/rspb.1998.0567 |pages=2251–2255}}</ref>

One branch would [[Evolution of cetaceans|evolve into cetaceans]], possibly beginning about {{mya|52|million years ago}}, with the protowhale ''[[Pakicetus]]'' and other early whale ancestors collectively known as [[Archaeoceti]]. This group eventually underwent [[aquatic adaptation]] into the completely aquatic [[cetacea]]ns.<ref name=Cetartiodactyla/> The other branch became the [[anthracotheriidae|anthracotheres]], a large family of four-legged beasts, the earliest of which in the late [[Eocene]] would have resembled skinny hippos with comparatively smaller, narrower heads. All branches of the anthracotheres, except that which evolved into [[Hippopotamidae]], became extinct during the [[Pliocene]], leaving no descendants.<ref name=ScienceNews/><ref name=Cetartiodactyla/>

A rough evolutionary lineage of the hippo can thus be traced from Eocene and [[Oligocene]] species: from ''[[Anthracotherium]]'' and ''[[Elomeryx]]'' to the [[Miocene]] species ''[[Merycopotamus]]'' and ''[[Libycosaurus]]'' and finally the very latest anthracotheres in the [[Pliocene]].<ref name=Origins>{{cite journal |last=Boisserie |first=J.-R. |author2=Lihoreau, F. |author3=Brunet, M. |year=2005 |title=Origins of Hippopotamidae (Mammalia, Cetartiodactyla): towards resolution |journal=[[Zoologica Scripta]] |volume=34 |issue=2 |pages=119–143 |doi=10.1111/j.1463-6409.2005.00183.x |s2cid=83768668}}</ref> These groups lived across Eurasia and Africa. The discovery of ''Epirigenys'' in East Africa, which was likely a descent of Asian anthracotheres and a [[sister taxon]] to Hippopotamidae, suggests that hippo ancestors entered Africa from Asia around {{Mya|35|million years ago}}.<ref>{{cite journal|author1=Lihoreau, F. |author2=Boisserie, J.-R. |author3=Manthi, F. K. |author4=Ducrocq. S. |year=2015 |title=Hippos stem from the longest sequence of terrestrial cetartiodactyl evolution in Africa |journal=Nature Communications |volume=6 |page=6264 |doi=10.1038/ncomms7264 |pmid=25710445 |bibcode=2015NatCo...6.6264L |doi-access=free}}</ref><ref>{{cite web |author=Lihoreau, F. |date=2015 |title=New Fossils from Kenya Precise Hippo Origin |publisher=Serious Science |access-date=5 June 2021|url=http://serious-science.org/new-fossils-from-kenya-precise-hippo-origin-2675}}</ref> An early hippopotamid is the genus ''[[Kenyapotamus]]'', which lived in Africa from 15 to {{mya|9|million years ago}}.<ref name=Origins/> Hippopotamid species would spread across Africa and Eurasia, including the modern pygmy hippo. From 7.5 to {{mya|1.8|million years ago}}, a possible ancestor to the modern hippo, ''[[Archaeopotamus]]'', lived in Africa and the Middle East.<ref name=Linnean>{{cite journal |last=Boisserie |first=J.-R. |year=2005 |title=The phylogeny and taxonomy of Hippopotamidae (Mammalia: Artiodactyla): a review based on morphology and cladistic analysis |journal=[[Zoological Journal of the Linnean Society]] |volume=143 |pages=1–26 |doi=10.1111/j.1096-3642.2004.00138.x |doi-access=free}}</ref> The oldest records of the genus ''[[Hippopotamus (genus)|Hippopotamus]]'' date to the [[Pliocene]] (5.3–2.6 million years ago).<ref name=VanDerMadeEtAl2017/> The oldest unambiguous records of the modern ''H. amphibius'' date to the [[Middle Pleistocene]], though there are possible [[Early Pleistocene]] records.<ref>{{Cite journal |last1=Pandolfi |first1=L. |last2=Martino |first2=R. |last3=Belvedere |first3=M. |last4=Martínez-Navarro |first4=B. |last5=Medin |first5=T. |last6=Libsekal |first6=Y. |last7=Rook |first7=L. |date=2023 |title=The latest Early Pleistocene hippopotami from the human-bearing locality of Buia (Eritrea) |journal=Quaternary Science Reviews |volume=308 |pages=108039 |doi=10.1016/j.quascirev.2023.108039|bibcode=2023QSRv..30808039P |s2cid=258024770}}</ref>
[[File:Malagasy Hippopotamus.jpg|thumb|right|''Choeropsis madagascariensis'' skeleton with a modern hippopotamus skull]]