genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
Hippopotamidae
Hippopotamidae is a family of stout, naked-skinned, and semiaquatic artiodactyl mammals, possessing three-chambered stomachs and walking on four toes on each foot. While they resemble pigs physiologically, their closest living relatives are t ...
that lived between 7.5 and 2.58 million years ago in
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
and the
Middle East
The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabian Peninsula, Arabia (including the Arabian Peninsula and Bahrain), Anatolia, Asia Minor (Asian part of Turkey except Hatay Pro ...
. The genus was described in 2005 to encompass species of hippos that were previously grouped in ''
Hexaprotodon
''Hexaprotodon'' is an extinct genus of hippopotamid known from Asia. The name ''Hexaprotodon'' means "six front teeth" as some of the fossil forms have three pairs of incisors.
''.
''Archaeopotamus'' means "the ancient of the river". Of all identified hippos, only ''
Kenyapotamus
''Kenyapotamus'' is a possible ancestor of living hippopotamuses that lived roughly 16 million to 8 million years ago during the Miocene epoch. Its name reflects that its fossils were first found in modern-day Kenya.
Although little is known ab ...
'' is older. ''Kenyapotamus'', however, is only known from partial fossils; ''Archaeopotamus'' is the oldest well-identified hippo.
Characteristics
Many prehistoric hippo fossils are known primarily through fossils of the
lower jaw
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
. ''Archaeopotamus'', like ''Hexaprotodon'', has three pairs of incisors. Unlike other ''Hexaprotodon'', ''Archaeopotamus'' has a highly elongate
mandibular symphysis
In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral halves ...
. The informal name "narrow muzzled hippos" has been suggested for this genus.
''A. lothagamensis''
''A. lothagamensis'' is a species whose fossils were discovered at Lothagam, a site southwest of
Lake Turkana
Lake Turkana (), formerly known as Lake Rudolf, is a lake in the Kenyan Rift Valley, in northern Kenya, with its far northern end crossing into Ethiopia. It is the world's largest permanent desert lake and the world's largest alkaline lake. B ...
in
Kenya
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and first described in 2000. When first described, the species was classified as ''Hexaprotodon lothagamensis'', although the significant morphological differences between other ''Hexaprotodon'' species, were noted.
''A. lothagamensis'' was smaller than the modern
hippopotamus
The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extan ...
and also smaller than ''A. harvardi'' and with a more slender skeleton. It was, however, significantly larger than the modern
pygmy hippopotamus
The pygmy hippopotamus or pygmy hippo (''Choeropsis liberiensis'') is a small hippopotamid which is native to the forests and swamps of West Africa, primarily in Liberia, with small populations in Sierra Leone, Guinea, and Ivory Coast. It has bee ...
.
''A. harvardi''
''A. harvardi'' is a species of hippo first described in 1977, originally as ''Hexaprotodon harvardi''. Although the proportions of ''A. harvardi'' and ''A. lothagamensis'' are similar, the former species is significantly smaller. Femurs of ''A. harvardi'' are approximately the same size as those of the modern hippopotamus.
Another group of fossils, originally described as ''Hexaprotodon sahabiensis'' or the Abu Dhabi Hippopotamus, are now considered to belong to ''A. harvardi'' or ''A. lothagamensis''. The fossil record for ''A. harvardi'' is more extensive than for other ''Archaeopotamus''.
''A. harvardi'' is believed to have had a more
riparian
A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks ar ...
lifestyle than ''A. lothagamensis''.
Distribution
Fossils of ''Archaeopotamus'' have been unearthed near
Lake Turkana
Lake Turkana (), formerly known as Lake Rudolf, is a lake in the Kenyan Rift Valley, in northern Kenya, with its far northern end crossing into Ethiopia. It is the world's largest permanent desert lake and the world's largest alkaline lake. B ...
, Kenya; near
Lake Victoria
Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropical lake, and the world's second-largest fresh water lake by surface area after ...
in Kenya and in
Abu Dhabi
Abu Dhabi (, ; ar, أَبُو ظَبْيٍ ' ) is the capital and second-most populous city (after Dubai) of the United Arab Emirates. It is also the capital of the Emirate of Abu Dhabi and the centre of the Abu Dhabi Metropolitan Area.
...
and thus likely ranged across
East Africa
East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territories make up Eastern Africa:
Due to the historical ...
and the
Arabian Peninsula
The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate ...
.
Evolution
The immediate ancestor of ''Archaeopotamus'' is unknown. Whether ''Archaeopotamus'' is descended from ''
Kenyapotamus
''Kenyapotamus'' is a possible ancestor of living hippopotamuses that lived roughly 16 million to 8 million years ago during the Miocene epoch. Its name reflects that its fossils were first found in modern-day Kenya.
Although little is known ab ...
'' cannot be determined from the few fossils available. Although ''Archaeopotamus'' is more primitive than any member of the genus ''Hippopotamus'', it is likely a sister group of both hippopotamuses and ''Hexaprotodon''.
Fossils similar to ''Archaeopotamus'' have been dated to as recently as about 2 million years ago, the end of the