Editing Pygmy hippopotamus (section)

== Taxonomy and origins ==
[[File:Hexaprotodon liberiensis Lagos Zoo Portugal (3).jpg|thumb|Showing its teeth at the [[Lagos, Portugal|Lagos]] Zoo in [[Portugal]] |left]]Nomenclature of the pygmy hippopotamus reflects that of the [[Hippopotamus#Taxonomy and origins|hippopotamus]]; the plural form is pygmy hippopotamuses or pygmy hippopotami.<ref>{{Cite web|url=https://www.thefreedictionary.com/Hippopotamus|title = Hippopotamus}}</ref> A male pygmy hippopotamus is known as a ''bull'', a female as a ''cow'', and a baby as a ''calf''.  A group of hippopotami is known as a ''herd'' or a ''bloat''.<ref>[[List of animal names]]</ref>

The pygmy hippopotamus is a member of the family [[Hippopotamidae]] where it is classified as a member of the [[genus]] ''Choeropsis'' ("resembling a [[Pig|hog]]"). Members of Hippopotamidae are sometimes known as hippopotamids. Sometimes the sub-family Hippopotaminae is used. Further, some taxonomists group hippopotami and [[anthracotheres]] in the superfamily Anthracotheroidea or Hippopotamoidea.

The [[Taxonomy (biology)|taxonomy]] of the genus of the pygmy hippopotamus has changed as understanding of the animal has developed.<ref name="Redlist"/><ref name="Linnean"/><ref name="The Hippos"/><ref name=Robinson/> [[Samuel G. Morton]] initially classified the animal as ''Hippopotamus minor'', but later determined it was distinct enough to warrant its own genus, and labeled it ''Choeropsis''. In 1977, [[Shirley C. Coryndon]] proposed that the pygmy hippopotamus was closely related to ''[[Hexaprotodon]]'', a genus that consisted of prehistoric hippos mostly native to Asia.<ref name=Coryndon/>

[[File:Pygmy Hippopotamus Skull.jpg|thumb|Skull]]This assertion was widely accepted,<ref name="Redlist"/><ref name="Linnean"/><ref name="The Hippos"/><ref name=Robinson/> until Boisserie asserted in 2005 that the pygmy hippopotamus was not a member of ''Hexaprotodon'', after a thorough examination of the phylogeny of Hippopotamidae. He suggested instead that the pygmy hippopotamus was a distinct genus, and returned the animal to ''Choeropsis''.<ref name="Linnean"/><ref name="Cetartiodactyla"/><ref name="Origins"/>  [[ITIS]] verifies ''Hexaprotodon liberiensis'' as the valid [[scientific name]].<ref name="ITIS">{{cite web |title=ITIS Standard Report Page: ''Hexaprotodon liberiensis'' |url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=625022#null |website=www.itis.gov |access-date=7 December 2020}}</ref>  All agree that the modern pygmy hippopotamus, be it ''H.&nbsp;liberiensis'' or ''C.&nbsp;liberiensis'', is the only extant member of its genus.<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><ref name=Coryndon>{{Cite journal |first=Shirley C.|last=Coryndon| title = The taxonomy and nomenclature of the Hippopotamidae (Mammalia, Artiodactyla) and a description of two new fossil species | year = 1977 | volume = 80 | issue = 2 | journal = Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen | pages = 61–88}}</ref> The [[American Society of Mammalogists]] moved it back to ''Choeropsis'' in 2021,<ref name=ASM>{{BioRef|asm|id=1006389|title=''Choeropsis liberiensis'' |version=1.5 |access-date=26 August 2021}}</ref> a move supported by the [[IUCN]].<ref name=Redlist/>

=== Nigerian subspecies ===
A distinct subspecies of pygmy hippopotamus existed in Nigeria until at least the 20th century, though the validity of this has been questioned.<ref name="Redlist"/> The existence of the subspecies, makes ''Choeropsis liberiensis liberiensis'' (or ''Hexaprotodon liberiensis liberiensis'' under the old classification) the full [[trinomen|trinomial nomenclature]] for the Liberian pygmy hippopotamus. The Nigerian pygmy hippopotamus was never studied in the wild and never captured. All research and all zoo specimens are the Liberian subspecies. The Nigerian subspecies is classified as ''C.&nbsp;liberiensis heslopi''.<ref name="The Hippos"/>

The Nigerian pygmy hippopotamus ranged in the [[Niger River|Niger River Delta]], especially near [[Port Harcourt]], but no reliable reports exist after the collection of the museum specimens secured by [[Ian Heslop]], a British colonial officer, in the early 1940s. It is probably extinct.<ref name="Redlist"/> The subspecies is separated by over {{convert|1800|km|mi|abbr=on}} and the [[Dahomey Gap]], a region of savanna that divides the forest regions of West Africa. The subspecies is named after Heslop, who shot three members of it in 1935 and 1943.<ref name=Enigma>{{cite book|author-last1=Robinson| author-first1=Phillip T.|author-last2=Flacke| author-first2=Gabriella L.| author-last3=Hentschel| author-first3= Knut M.| year=2017| title=The Pygmy Hippo Story: West Africa's Enigma of the Rainforest| publisher=Oxford University Press| place=Oxford| isbn=978-0-19-061185-9|pages=61, 65}}</ref> He estimated that perhaps no more than 30 pygmy hippos remained in the region.<ref name=Action>{{Cite web | url = http://www.iucn.org/themes/ssc/sgs/pphsg/APchap3-3.htm | archive-url = https://archive.today/20080105044155/http://www.iucn.org/themes/ssc/sgs/pphsg/APchap3-3.htm | url-status = dead | archive-date = 2008-01-05 | title = Pigs, Peccaries and Hippos Status Survey and Action Plan | year = 1993 | access-date = 2008-08-23 | work = [[World Conservation Union]] status survey | author = Eltringham, S. Keith}}</ref>

Heslop sent four pygmy hippopotamus skulls he collected to the [[British Museum of Natural History]] in London. These specimens were not subjected to taxonomic evaluation, however, until 1969 when {{Ill|Gordon Barclay Corbet|de}} classified the skulls as belonging to a separate subspecies based on consistent variations in the proportions of the skulls.<ref name=Corbet>{{Cite journal| title = The taxonomic status of the pygmy hippopotamus, Choeropsis liberiensis, from the Niger Delta | author = Corbet, G. B. | journal = [[Journal of Zoology]] | year = 1969 | volume = 158 | issue = 3 | pages = 387–394| doi = 10.1111/j.1469-7998.1969.tb02156.x}}</ref> The Nigerian pygmy hippos were seen or shot in [[Rivers State]], [[Imo State]] and [[Bayelsa State]], [[Nigeria]]. While some local humans are aware that the species once existed, its history in the region is poorly documented.<ref name="The Hippos"/>

=== Evolution ===
{{main|Hippopotamus#Evolution}}
[[File:Anthracotherium magnum.jpg|thumb|[[Anthracothere]]s like ''[[Anthracotherium]]'' resembled pygmy hippos and are among their likely ancestors.]]
The evolution of the pygmy hippopotamus is most often studied in the context of its larger cousin. Both species were long believed to be most closely related to the family [[Suidae]] ([[pig]]s and hogs) or Tayassuidae ([[peccaries]]), but research within the last 10 years has determined that pygmy hippos and hippos are most closely related to [[cetacea]]ns ([[whale]]s and [[dolphin]]s). Hippos and whales shared a common semi-aquatic ancestor that branched off from other artiodactyls around {{mya|60|mya}}.<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=2008-08-23 |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><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]] | volume = 14 | pages = 537–543 | pmid = 9159931 | issue = 5 | date=1 May 1997 | doi=10.1093/oxfordjournals.molbev.a025790| doi-access = free }}</ref>

This hypothesized ancestor likely split into two branches about six million years later.<ref name="Genomes">{{Cite journal | title = Analyses of mitochondrial genomes strongly support a hippopotamus-whale clade | volume = 265 | issue = 1412 | year = 1998 | pages = 2251–5 | journal = [[Proceedings of the Royal Society]] | author = Ursing, B.M. |author2=U. Arnason  | doi = 10.1098/rspb.1998.0567 | pmid = 9881471 | pmc = 1689531}}</ref> One branch would [[Evolution of cetaceans|evolve into cetaceans]], the other branch became the [[anthracotheriidae|anthracotheres]], a large family of four-legged beasts, whose earliest member, from the Late [[Eocene]], would have resembled narrow hippopotami with comparatively small and thin heads.<ref name="Cetartiodactyla">{{cite journal |last=Boisserie |first=Jean-Renaud |author2= Fabrice Lihoreau |author3=Michel Brunet |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|pmid= 15677331 |pmc=547867|bibcode=2005PNAS..102.1537B |doi-access=free }}</ref>

Hippopotamids are deeply nested within the family [[Anthracotheriidae]]. The oldest known hippopotamid is the genus ''[[Kenyapotamus]]'', which lived in Africa from {{mya|16|8|mya}}. ''Kenyapotamus'' is known only through fragmentary fossils, but was similar in size to ''C.&nbsp;liberiensis''.<ref name="Origins">{{cite journal | last= Boisserie | first=Jean-Renaud | author2=Fabrice Lihoreau |author3=Michel Brunet |date=March 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> The Hippopotamidae are believed to have evolved in Africa, and while at one point the species spread across Asia and Europe, no hippopotami have ever been discovered in the Americas. Starting {{mya|7.5|1.8|mya}} the ''[[Archaeopotamus]]'', likely ancestors to the genus ''Hippopotamus'' and ''[[Hexaprotodon]]'', lived in Africa and the Middle East.<ref name="Linnean"/>

While the fossil record of hippos is still poorly understood, the lineages of the two modern genera, ''[[Hippopotamus (genus)|Hippopotamus]]'' and ''Choeropsis'', may have diverged as far back as {{mya|8|mya}}. The ancestral form of the pygmy hippopotamus may be the genus ''Saotherium''. ''Saotherium'' and ''Choeropsis'' are significantly more [[Basal (phylogenetics)|basal]] than ''Hippopotamus'' and ''Hexaprotodon'', and thus more closely resemble the ancestral species of hippos.<ref name="Linnean"/><ref name="Origins"/>

=== Extinct pygmy and dwarf hippos ===
Several species of small hippopotamids have also become extinct in the Mediterranean in the late [[Pleistocene]] or early [[Holocene]]. Though these species are sometimes known as "pygmy hippopotami" they are not believed to be closely related to ''C.&nbsp;liberiensis''. These include the [[Cretan Dwarf Hippopotamus|Cretan dwarf hippopotamus]] (''Hippopotamus creutzburgi''), the Sicilian hippopotamus (''[[Hippopotamus pentlandi]]''), the Maltese hippopotamus (''[[Hippopotamus melitensis]]'') and the [[Cyprus Dwarf Hippopotamus|Cyprus dwarf hippopotamus]] (''Hippopotamus minor'').<ref name="Taxonomy of Pleistocene">{{cite journal|last=Petronio |first=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 |access-date=2008-08-23 |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=2008-09-12 }}</ref>

These species, though comparable in size to the pygmy hippopotamus, are considered dwarf hippopotamuses, rather than pygmies. They are likely descended from a full-sized species of [[Hippopotamus antiquus|European hippopotamus]], and reached their small size through the evolutionary process of [[insular dwarfism]] which is common on islands; the ancestors of pygmy hippopotami were also small and thus there was never a dwarfing process.<ref name="Taxonomy of Pleistocene"/> There were also several species of pygmy hippopotamus on the island of [[Madagascar]] (see [[Malagasy Hippopotamus|Malagasy hippopotamus]]).