Editing Hippopotamus (section)

==Taxonomy and origins==

===Classification===
{{multiple image
 | direction         = vertical
 | image1 = Hipopótamo (Hippopotamus amphibius), parque nacional de Chobe, Botsuana, 2018-07-28, DD 60.jpg
|alt1=Closeup photo, top of head, feeding while partially submerged
 | image2            = Hippopotamus amphibius 3d scan Natural History Museum University of Pisa C 228.stl
|alt2=Interactive 3D partial skull scan
 | image3            = Hippopotamus amphibius (mandible) 3d scan Natural History Museum University of Pisa C228.stl
|alt3=Interactive 3D scan of the remaining mandible
 | footer            = Head, skull and mandible of ''Hippopotamus amphibius''
}}
The modern hippopotamus and the [[pygmy hippopotamus]] are the only living members of the family Hippopotamidae. Some taxonomists place hippos and [[anthracotheres]] in the superfamily Anthracotheroidea. Hippopotamidae are classified along with other [[even-toed ungulates]] in the [[order (biology)|order]] [[Artiodactyla]].<ref name="The Hippos"/>{{rp|39–40}}

Five subspecies of hippos have been described based on [[morphology (biology)|morphological]] differences in their skulls as well as differences in geographical range:<ref name="The Hippos"/>{{rp|3}}<ref>{{cite book|author=Lydekker, R|year=1915|title=Catalogue of the Ungulate Mammals in the British Museum of Natural History, vol. 4|volume=4 |publisher=British Museum|pages=389–392|url=https://www.biodiversitylibrary.org/item/114771#page/417/mode/1up}}</ref><ref name="Okello"/><ref>{{Cite journal|title = Suiform Soundings: The IUCN/SSC Pigs, Peccaries, and Hippos Specialist Group (PPHSG) Newsletter|volume = 5|issue = 1|date=September 2005|url = https://www.scribd.com/document/65917875/Newsletter-5-1 |format=PDF |journal = [[World Conservation Union|IUCN]]|editor = Meijaard, Erik}}</ref>
*''H. a. amphibius'' – (the nominate subspecies) ranges from [[Gambia]] east to [[Ethiopia]] and then south to [[Mozambique]] and historically ranged as far north as Egypt; its skull is distinguished by a moderately reduced preorbital region, a bulging dorsal surface, elongated [[mandibular symphysis]] and larger chewing teeth.
*''H. a. kiboko'' – found in [[Kenya]] and [[Somalia]]; was noted to be smaller and more lightly coloured than other hippos with wider nostrils, somewhat longer snout and more rounded and relatively raised [[Orbit (anatomy)|orbit]]s with the space between them being incurved.
*''H. a. capensis'' – found in [[Zambia]] and [[South Africa]]; distinguished by wider orbits.
*''H. a. tschadensis'' – ranges between [[Chad]] and [[Niger]]; featured a slightly shorter but broader face, and pronounced, forward-facing orbits.
*''H. a. constrictus'' – ranged from the southern [[Democratic Republic of Congo]] to [[Angola]] and [[Namibia]]; skull characterised by a thicker preorbital region, shorter snout, flatter dorsal surface, reduced mandibular symphysis and smaller chewing teeth.
The suggested subspecies above were never widely used or validated by field biologists; the described morphological differences were small enough that they could have resulted from simple variation in nonrepresentative samples.<ref name="The Hippos">{{cite book |last=Eltringham |first=S. K. |title=The Hippos: Natural History and Conservation |year=1999 |publisher=Academic Press |isbn=978-0-85661-131-5 |series=Poyser Natural History Series}}</ref>{{rp|2}} A study examining [[mitochondrial DNA]] from skin biopsies taken from 13 sampling locations found "low, but significant, genetic differentiation" among ''H. a. amphibius'', ''H. a. capensis'', and ''H. a. kiboko''. Neither ''H. a. tschadensis'' nor ''H. a. constrictus'' have been tested.<ref name=Okello>{{Cite journal |author=Okello, J. B. A. |author2=Nyakaana, S. |author3=Masembe, C. |author4=Siegismund, H. R. |author5=Arctander, P. |year=2005 |title=Mitochondrial DNA variation of the common hippopotamus: evidence for a recent population expansion |journal=[[Heredity (journal)|Heredity]] |pmid=16030528 |volume =95 |issue=3 |pages=206–215 |doi=10.1038/sj.hdy.6800711 |doi-access=free|bibcode=2005Hered..95..206O }}</ref>

===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]]

===Extinct species===
Three species of [[Malagasy hippopotamus]] became extinct during the [[Holocene]] on [[Madagascar]], the last of them within the past 1,000 years. The Malagasy hippos were smaller than the modern hippo, a likely result of the process of [[insular dwarfism]].<ref name=Stuenes>{{Cite journal |doi=10.1080/02724634.1989.10011761 |author=Stuenes, S. |year=1989 |title=Taxonomy, habits and relationships of the sub-fossil Madagascan hippopotamuses ''Hippopotamus lemerlei'' and ''H. madagascariensis'' |journal=[[Journal of Vertebrate Paleontology]] |volume=9 |pages=241–268 |issue=3}}</ref> Fossil evidence indicates many Malagasy hippos were hunted by humans, a factor in their eventual extinction.<ref name=Stuenes/> Isolated individual Malagasy hippos may have survived in remote pockets; in 1976, villagers described a living animal called the ''kilopilopitsofy'', which may have been a Malagasy hippo.<ref name=Kidoky>{{Cite journal |title=The Kilopilopitsofy, Kidoky, and Bokyboky: Accounts of Strange Animals from Belo-sur-mer, Madagascar, and the Megafaunal "Extinction Window" |journal=[[American Anthropologist]] |year=1998 |author=Burney, D. A. |jstor=681820 |volume=100 |issue=4 |pages=957–966 |author2=Ramilisonina |doi=10.1525/aa.1998.100.4.957}}</ref>

''[[Hippopotamus gorgops]]'' from the Early Pleistocene to the early Middle Pleistocene of Africa and West Asia grew considerably larger than the living hippopotamus, with an estimated body mass of over {{Cvt|4000|kg}}.<ref name=VanDerMadeEtAl2017>van der Made J, Sahnouni M & Boulaghraief K. 2017. [https://www.mncn.csic.es/sites/default/files/inline-files/2017%20Van%20der%20Made%20ea%20-%20Hippopotamus%20-%20El%20Kherba%20-%20ProcIIMeetingAfrPrehist.pdf ''Hippopotamus gorgops'' from El Kherba (Algeria) and the context of its biogeography]. In Proceedings of the II Meeting of African Prehistory: Burgos 15–16 April 2015, Sahnouni M, Semaw S, Rios Garaizar J (eds). CENIEH: Burgos; 135–169.</ref><ref>Chaix L, Faure M, Guérin C, Honegger M. [https://kerma.ch/documents/Publications_PDF/Chaix_Faure_Guerin_Honegger_Kaddanarti_2000.pdf Kaddanarti, a Lower Pleistocene Assemblage from Northern Sudan]. In: Krzyżaniak L, Kroeper K, Kobusiewicz M, editors. Recent Research into the Stone Age of Northeastern Africa. Poznań: Poznań Archaeological Museum; 2000. p. 33–46.</ref><ref>{{Cite journal |last=Hutchinson |first=J. R. |date=2021 |title=The evolutionary biomechanics of locomotor function in giant land animals |journal=Journal of Experimental Biology |volume=224 |issue=11 |doi=10.1242/jeb.217463 |issn=0022-0949 |pmc=8214834 |pmid=34100541|bibcode=2021JExpB.224B7463H }}</ref> ''[[Hippopotamus antiquus]]'' ranged throughout Europe, extending as far north as Britain during the [[Early Pleistocene|Early]] and [[Middle Pleistocene]] epochs, before being replaced by the modern ''H. amphibius'' in Europe during the latter part of the Middle Pleistocene.<ref>{{Cite journal |last1=Adams|first1=N. F. |last2=Candy |first2=I. |last3=Schreve |first3=D. C.|title=An Early Pleistocene hippopotamus from Westbury Cave, Somerset, England: support for a previously unrecognized temperate interval in the British Quaternary record |journal=Journal of Quaternary Science |year=2022 |volume=37 |issue=1 |pages=28–41 |doi=10.1002/jqs.3375 |bibcode=2022JQS....37...28A |s2cid=244179438 |doi-access=free}}</ref> The Pleistocene also saw a number of dwarf species evolve on several Mediterranean islands, including [[Crete]] (''[[Hippopotamus creutzburgi]]''), [[Cyprus]] (the [[Cyprus dwarf hippopotamus]], ''Hippopotamus minor''), [[Malta]] (''[[Hippopotamus melitensis]]''), and [[Sicily]] (''[[Hippopotamus pentlandi]]''). Of these, the Cyprus dwarf hippo survived until the end of the Pleistocene or early Holocene. Evidence from the archaeological site [[Aetokremnos]] continues to cause debate on whether or not the species was driven to extinction or even encountered by humans.<ref>{{Cite journal |author=Simmons, A. |year=2000 |title=Faunal extinction in an island society: pygmy hippopotamus hunters of Cyprus |journal=[[Geoarchaeology]] |volume=15 |issue=4 |pages=379–381 |doi=10.1002/(SICI)1520-6548(200004)15:4<379::AID-GEA7>3.0.CO;2-E |bibcode=2000Gearc..15..379G}}</ref><ref name="Taxonomy of Pleistocene">{{cite journal |author=Petronio, C. |year=1995 |title=Note on the taxonomy of Pleistocene hippopotamuses |journal=Ibex |volume=3 |pages=53–55  |url=http://www.mountainecology.org/IBEX3/pdf/Art_Capitolo1/note_taxonomy_pleistocene.pdf |url-status=dead |archive-url=https://web.archive.org/web/20080912012236/http://www.mountainecology.org/IBEX3/pdf/Art_Capitolo1/note_taxonomy_pleistocene.pdf|archive-date=12 September 2008}}</ref>