Editing Hippopotamus (section)

===Classification===
{{multiple image
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 | 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''
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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>