Editing Hippopotamidae (section)

== Evolution ==
{{Main|Hippopotamus#Evolution|l1=Evolution of hippopotamids}}
[[File:Hippopotamus_amphibius_Linn_at_Ghar_Dalam,_Malta.png|thumb|right|Hippopotamus skeleton at [[Għar Dalam]]]]
The hippopotamids are descended from the [[anthracothere]]s, a family of semiaquatic and terrestrial artiodactyls that appeared in the late [[Eocene]], and are thought to have resembled small- or narrow-headed hippos.  The hippos split off from the anthracotheres some time during the [[Miocene]]. The oldest records of Hippopotamidae are from Afro-Arabia and date to the late Miocene, approximately 7.4 million years ago, expanding into Eurasia around 6 million years ago.<ref>{{Cite journal |last1=Martino |first1=R. |last2=Pandolfi |first2=L. |date=2022-07-03 |title=The Quaternary Hippopotamus records from Italy |url=https://www.tandfonline.com/doi/full/10.1080/08912963.2021.1965138 |journal=Historical Biology |language=en |volume=34 |issue=7 |pages=1146–1156 |doi=10.1080/08912963.2021.1965138 |bibcode=2022HBio...34.1146M |s2cid=239713930 |issn=0891-2963}}</ref> After the appearance of the hippopotamids, the remaining anthracotheres went into a decline brought about by a combination of climatic change and competition with their descendants, until the last genus, ''[[Merycopotamus]]'', died out in the early [[Pliocene]] of India.

There were once many species of hippopotamid, but only two survive today: ''Hippopotamus amphibius'', and ''Choeropsis liberiensis''. They are the last survivors of two major [[evolution]]ary lineages, the hippos proper and the pygmy hippos, respectively; these lineages could arguably be considered [[subfamilies]], but their relationship to each other – apart from being fairly distant relatives – is not well resolved.

The enigmatic [[Miocene]] ''[[Kenyapotamus]]'' is insufficiently known to be assigned a place in the hippo [[phylogeny]] with any degree of certainty. In addition, the genus ''[[Hexaprotodon]]'', which is now largely restricted to South Asia and Southeast Asia, formerly included many fossil hippopotamuses that are now thought to be unrelated.<ref name="Linnean">{{cite journal |last=Boisserie |first=Jean-Renaud |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>

=== Taxonomy ===
Hippopotamidae's placement within [[Artiodactyla]] can be represented in the following [[cladogram]]:<ref>
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}} (see fig&nbsp;S10).
</ref>

{{Clade
     |style=font-size:100%;line-height:100%
     |label1=[[Artiodactyla]]
     |1={{Clade
         |1=[[Tylopoda]] (camels and kin) [[File:Cladogram of Cetacea within Artiodactyla (Camelus bactrianus).png|50 px]]
         |label2=[[Artiofabula]]
         |2={{Clade
               |1=[[Suina]] (pigs and kin) [[File:Recherches pour servir à l'histoire naturelle des mammifères (Pl. 80) (white background).jpg|50 px]]
               |label2=[[Cetruminantia]]
               |2={{Clade
                   |1=[[Ruminantia]] (ruminants) [[File:Walia ibex illustration white background.png|50 px]]
                   |label2=[[Whippomorpha]]
                   |sublabel2=(or Cetancodonta)
                   |2={{Clade
                      |1='''Hippopotamidae''' (hippopotamids) [[File:Voyage en Abyssinie Plate 2 (white background).jpg|50 px]]
                      |2=[[Cetacea]] (whales) [[File:Bowhead-Whale1 (16273933365).jpg|50 px]]
                      }}
                  }}
               }}
            }}
         }}

=== Analogous structures ===
The lower canine teeth of hippopotamids are similar in function and structure to the tusks of [[elephant]]s. While hippopotamids and elephants are only very distantly related within the Mammalia, the lower canine teeth of both groups are long and have a slight curve, and species of both families use this structure when fighting.