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''Brachyhyops'' is an extinct genus of
entelodont Entelodontidae is an extinct family of pig-like artiodactyls (even-toed ungulates) which inhabited the Northern Hemisphere (Asia, Europe, and North America) from the late Eocene to the early Miocene epochs, about 38-19 million years ago. Their ...
artiodactyl Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other t ...
mammal that lived during the
Eocene Epoch The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', 'Dawn') and ...
of western North America and southeastern Asia (including Mongolia, China, and Kazakhstan).Colbert, E.H. (1937). Notice of a new genus and species of Artiodactyl from the Upper Eocene of Wyoming. American journal of Science, Series 5, 33: 473-474Colbert, E.H. (1938). Brachyhyops, a new bunodont artiodactyls from Beaver Divide, Wyoming: Annals of the Carnegie Museum. Vol. 27. 87-108Wang, B.-Y., Qiu, Z.-X. (2002). A new species of Entelodontidae (Artiodactyla, Mammalia) from the late Eocene of Nei Mongol, China. Vertebrata PalAsiatica, vol. 40, p. 194-202 (in Chinese with English summary) The first fossil remains of ''Brachyhyops'' are recorded from the late Eocene deposits of Beaver Divide in central Wyoming and discovered by paleontology crews from the
Carnegie Museum of Natural History The Carnegie Museum of Natural History (abbreviated as CMNH) is a natural history museum in the Oakland (Pittsburgh), Oakland neighborhood of Pittsburgh, Pennsylvania. It was founded by List of people from the Pittsburgh metropolitan area, Pit ...
during the early 20th century. The type species, ''Brachyhyops wyomingensis'', is based on a single skull and was named by E.H. Colbert in 1937, but was not officially described until 1938. During the latter half of the 20th century, additional specimens from North America have been recorded from Saskatchewan and as far south as Texas, indicating that ''Brachyhyops'' had a broad distribution and was well-dispersed throughout western North America. More recent discoveries from Eocene deposits in Mongolia lead to the recognition of a second species of ''Brachyhyops'', ''B trofimovi''.Tsubamoto, T., Saneyoshi, M., Watabe, M., Tsogbataar, K., Mainbayar, B. (2011). The Entelodontid Artiodactyl Fauna from the Eocene Ergilin Dzo Formation of Mongolia with Comments on Brachyhyops and the Khoer Dzan Locality. Paleontological Research, 15(4):258-268 It is notable that the oldest specimens of ''Brachyhyops'' are middle Eocene in age and have been recorded exclusively from southern Asia, whereas specimens from the late Eocene only occur in the northern part of the continent. This implies that the genus ''Brachyhyops'' most likely originated in southern Asia, migrated north and eventually dispersed into western North America.


Discovery

In 1934, crew members of the Carnegie Museum paleontological expedition discovered the holotype of ''Brachyhyops wyomingensis'' (CM 12048) from the uppermost beds of the Eocene
White River Formation The White River Formation is a geologic formation of the Paleogene Period, in the northern Great Plains and central Rocky Mountains, within the United States. It has been found in northeastern Colorado, Dawes County in western Nebraska, Badland ...
, in a member known as the Big Sand Draw Sandstone Lentil, at Beaver Divide, Wyoming.Prothero, D.R., Sanchez, F. (2004). Magnetic stratigraphy of the middle to upper Eocene at Beaver Divide, Fremont County, Central Wyoming. In Lucas, S.S., Zeigler, K.E., Kondrashov, P.E. (eds.) Paleogene Mammals. New Mexico Museum of Natural History and Science Bulletin No. 26, 151-154 The specimen consists of a single, exceptionally well preserved, but severely distorted, isolated skull with no
mandibles In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...
or post cranial material. Since its initial discovery, several other partial specimens of ''Brachyhyops'' have been recorded within North America and Asia. Currently, four species of ''Brachyhyops'' have been recognized; two from Asia and two within North America, and include ''Brachyhyops trofimovi'' from Mongolia, ''B. neimongoliensis'' from northern China, ''B. viensis'' from Saskatchewan, Canada; Wyoming, and New Mexico, USA, and lastly, ''B. wyomingensis'' from Wyoming, Utah, and Texas, USA.


Description

Holotype (CM 12048) of ''Brachyhyops wyomingensis'' was diagnosed by Edwin H. Colbert in 1938 as a medium sized skull with a relatively short snout and a length that is comparable to the skull of a modern peccary. The portion of the skull behind the eye socket is greater compared to the portion of the skull in front of the eye socket due to the short size of the snout. The dentition is I3(?)-C1-P4-M3, indicating in the upper jaw the number of incisors, canines, premolars, and molars respectively. Colbert compared ''B. wyomingensis'' to ''Helohyus'', ''Chaeropotamus'', ''Achaenodon'', and ''Parahyus'' based on tooth shape. No mandibles were preserved with the holotype specimen and therefore dentition of the lower jaws could not be determined. The overall width of the skull is broad and having widely separated parietal crests. In addition, the
zygomatic arches In anatomy, the zygomatic arch (colloquially known as the cheek bone), is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal ...
are deepened and expanded below and behind the eye socket, contributing to the wide skull shape, which is very similar to other entelodonts. The rear portion of eye socket is closed and situated directly above the last two molars. Articulation surfaces for the lower jaws; the glenoids, are broad, shallow, and situated around the occlusal line of the upper cheek teeth. Both paroccipital processes are short and parietals are weakly developed. The
basicranium The base of skull, also known as the cranial base or the cranial floor, is the most inferior area of the skull. It is composed of the endocranium and the lower parts of the calvaria. Structure Structures found at the base of the skull are for ...
, or occiput, is considered basal.


Classification and Evolution

''Brachyhyops'' is an artiodactyl which has a poorly resolved evolutionary status that continues to be subject of revision. Colbert initially classified ''Brachyhyops'' strictly within the bunodontids based on its bunodont-like tooth shape. More recent studies revised the evolutionary relationship of ''Brachyhyops'' and it has now been recognized as a very basal entelodontid that might represent the origin of the clade Entelodontidae, which also includes members such as the
Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...
''
Archaeotherium ''Archaeotherium'' (, meaning "ancient beast") is an extinct genus of entelodont artiodactyl endemic to North America during the Eocene and Oligocene epochs (35–28 mya). ''Archaeotherium'' fossils are most common in the White River Formation ...
'' and
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
''
Daeodon ''Daeodon'' is an extinct genus of entelodont even-toed ungulates that inhabited North America about 29 to 15.97 million years ago from the early Oligocene to late early Miocene. The type species is ''Daeodon shoshonensis'', described from a ve ...
''.


Taxonomy

''Brachyhyops'' was named by Colbert (1937) lso said to be 1938 The type species is ''B. wyomingensis.'' It was assigned to ''Artiodactyla'' by Colbert (1937); assigned to Suina by Effinger (1998), and was assigned to ''
Entelodontidae Entelodontidae is an extinct family of pig-like artiodactyls (even-toed ungulates) which inhabited the Northern Hemisphere (Asia, Europe, and North America) from the late Eocene to the early Miocene epochs, about 38-19 million years ago. Their ...
'' by Carroll (1988).


Merger with ''Eoentelodon''

''
Eoentelodon ''Eoentelodon'' is a small, primitive entelodont, assigned as such by Carroll (1998), from the Middle Eocene of China. It was a very small entelodont, about the size of a modern pig, and was slightly smaller than its North American counterpart ...
'' was synonymized subjectively with ''Brachyhyops'' by Lucas and Emry (2004) as "Brachyhyops yunnanensis." However, in 2007, I. Vislobokova determined that ''Eoentelodon'' was not only distinct from ''Brachyhyops'', but more closely related to ''
Proentelodon ''Proentelodon'' is an extinct genus of entelodont artiodactyl from the Middle Eocene of Mongolia. ''P. minutus'' is the oldest representative of the family Entelodontidae Entelodontidae is an extinct family of pig-like artiodactyls (even-to ...
'', another primitive entelodont found in slightly older Middle Eocene strata of
Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...
, and placed ''Eoentelodon'' and ''Proentelodon'' in their own subfamily, Proentelodontinae.I. A. Vislobokova.The oldest representative of Entelodontoidea (Artiodactyla, Suiformes) from the Middle Eocene of Khaichin Ula II, Mongolia, and some evolutionary features of this superfamily Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997, Russi

/ref>


Fossil distribution

Fossils have been uncovered from
Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...
to
Uintah County, Utah Uintah County ( ) is a County (United States), county in the U.S. state of Utah. As of the 2020 United States census the population was 35,620. Its county seat and largest city is Vernal, Utah, Vernal. The county was named for the portion of t ...
to
Saskatchewan, Canada Saskatchewan is a province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the United States (Montana and North Dako ...
as well as
Jiangsu Jiangsu is a coastal Provinces of the People's Republic of China, province in East China. It is one of the leading provinces in finance, education, technology, and tourism, with its capital in Nanjing. Jiangsu is the List of Chinese administra ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
.


Paleobiogeography


Asian distribution

The oldest fossil material that is assigned to ''Brachyhyops'' is early to upper Eocene in age, and recorded from six Asian localities, predominantly Mongolia, China, with the lone exception of a single location in Kazakhstan. Currently, two localities in southern Asia yield the oldest ''Brachyhyops'' material known. The first locality is situated in the northwestern Yunnan of southern China, and specimens of ''Brachyhyops'' sp. are recorded from the early middle, or late middle Eocene Xiangshan Formation. No ''Brachyhyops'' specimens from the lower to middle Eocene have been recorded from northern Asia; instead, the four remaining localities are all younger (late Eocene) in age and include the southeastern Mongolian taxa ''B. trofimovi'' from the
Ergilin Dzo Formation The Ergilin Dzo Formation (formerly known as the Ardyn Obo Formation), is a geologic formation in southeastern Mongolia. It preserves fossils of a wide variety of animals, which date back to the late Eocene epoch. The type fauna of the Ergilian ...
at the Khoer Dzan locality and ''Brachyhyops?'' sp. from the Ergilin Dzo Formation at the Ergilin Dzo locality. A single taxon, ''B. neimongolensis'', is recorded from the upper Eocene Ulan Gochu Formation of northern China. Lastly, material assigned to ‘''Eoentelodon'' sp.’ (revised as ''Brachyhyops'' sp. by Tsubamoto et al.) is recorded from the lower Aksyir ‘svita’ in eastern Kazakhstan, which was later correlated to the late Eocene Ergilian Asian Land Mammal ‘age’ (ALMA) by Emry et al.Emry, R.J., Lucas, S.G., Tyutkova, L., Wang, B. (1998). The Ergilian-Shandgolian (Eocene-Oligocene) transition in the Zaysan basin, Kazakhstan. Bulletin of Carnegie Museum of Natural History, no. 34, p. 298-312 and Lucas et al.Lucas, S.G., Emry, R.J., Bayshashov, B.U., Tyutkova, L.A. (2009). Cenozoic mammalian biostratigraphy and biochronology in the Zaysan basin, Kazakhstan. Museum of Northern Arizona Bulletin, no. 65, p. 621-633


North American distribution

''Brachyhyops'' is the oldest entelodont from North America and is recorded exclusively from late Eocene (late
Duchesnean The Duchesnean North American Stage on the geologic timescale is a North American Land Mammal Age (NALMA), with an age from 42 to 38 million years BP, representing . It falls within the Eocene epoch. The Duchesnean is preceded by the Uintan and f ...
– early
Chadronian The Chadronian is a North American Land Mammal Age typically set from around 37,000,000 to 33,700,000 years BP, a period of . The Chadronian is preceded by the Duchesnean and followed by the Orellan NALMA stages. Relative to global geological c ...
) age deposits.Lucas, S.G., Emry, R.J. (2004). The entelodont Brachyhyops (Mammalia, Artiodactyla) from the upper Eocene of Flagstaff Rim, Wyoming. New Mexico Museum of Natural History and Science Bulletin, no. 26, p. 97-100 Their geographic range is restricted to western North America and spans from Saskatchewan, Canada to as far south as Big Bend, Texas, USA. A total of nine localities have yielded ''Brachyhyops'' material. The Cypress Hills Formation in Saskatchewan, Canada, suggests an early Chadronian age, approximately 37 Ma, and represents the type locality for ''Brachyhyops viensis'' as well as the northernmost area in which ''Brachyhyops'' specimens have been recorded. Apparently an undocumented ''Brachyhyops'' specimen has been recorded from the late Eocene White River Formation of Montana, however, the exact museum location where this specimen is housed remains unknown. Three localities in Wyoming yielded ''Brachyhyops'' material and these include a partial skull roof and maxilla from the lower White River Formation (late Eocene) of the Flagstaff Rim, Wyoming. Based on size and tooth shape, these specimens have been assigned to ''B. viensis''. The next locality in Wyoming is the type locality for ''B. wyomingensis'' which was recorded from the Big Sand Draw Lentil of the White River Formation at Beaver Divide, and comprises a single skull without mandibles. The third locality yielded cranial fragments that are assigned to ''B. viensis'' and were recorded from the lower strata of the White River Formation at Canyon Creek, approximately 50 km east of Beaver Divide. Additional ''Brachyhyops wyomingensis'' material was recorded from a single location in northeastern Utah, namely the Lapoint Member of the Duchesne River Formation, which has an age of approximately 39.74 ± 0.07 Ma based on radioisotopic dates from nearby volcanic ashes. Two localities within New Mexico yielded ''Brachyhyops'' material and include a single molar (m1) from the lower jaw that was assigned to ''B. viensis'' and recorded within the Duchesnean interval of the Galisteo Formation in north central New Mexico, and is of late Duchesnean (38 Ma) age. An additional specimen was recorded from the upper Baca Formation at Mariano Mesa in west central New Mexico and is also situated within the Duchesnean. This specimen comprises a single premolar and four molars (p3 – m4) from a single right lower jaw and are assigned to ''B. wyomingensis'' based on the shape and dimensions of the teeth. The final locality within North America is located in Trans-Pecos, Texas, USA, and contains well documented records of ''Brachyhyops wyomingensis'' from the late Duchesnean Porvenir local fauna which is situated above a volcanic ash that is radioisotopically dated to 37.8 ± 0.15 Ma. The fact that there is no stratigraphic overlap between northern and southern Asian ''Brachyhyops'' specimens, suggests that ''Brachyhyops'' originated in southern Asia during the early and late middle Eocene and continuously dispersed into northern Asia. Long term exposure of the Beringian land bridge during the late Eocene promoted continuous intercontinental dispersal from Asia into North America, resulting in further dispersal and diversification of ''Brachyhyops'' across western North America during the late Eocene.


Diet

The dentition of ''Brachyhyops'' is
heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. Human dentition is heterodont and diphyodont as an example. In vertebrates, heterodont pertains to animals wher ...
, which forms a complex set of different teeth including incisors, large canines, premolars, and molars, which are used to capture and process a wide variety of food items including both meat and vegetation. Despite their heterodont tooth condition, there has been a considerable amount of debate regarding the diet of ''Brachyhyops'' and various other entelodontids with similar dentition, such as ''
Archaeotherium ''Archaeotherium'' (, meaning "ancient beast") is an extinct genus of entelodont artiodactyl endemic to North America during the Eocene and Oligocene epochs (35–28 mya). ''Archaeotherium'' fossils are most common in the White River Formation ...
'' and ''
Daeodon ''Daeodon'' is an extinct genus of entelodont even-toed ungulates that inhabited North America about 29 to 15.97 million years ago from the early Oligocene to late early Miocene. The type species is ''Daeodon shoshonensis'', described from a ve ...
''. Researchers have proposed different dietary hypotheses based on the heterodont dentition and shape of the teeth, interpreting entelodontids as rooting, pig-like
omnivores An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize t ...
,Scott, W.B. (1940). The mammalian fauna of the White River Oligocene, Part IV: Artiodactyla. Transacrions of the American Philosophical Society, New Series 28:363-746Romer, A.S. (1966). Vertebrate Paleontology. University of Chicago Press; Chicago browsersRussell, L.S.(1980). Tertiary mammals of Saskatchewan part V; The Oligocene Entelodonts. Life Science s Contributions of the Royal Ontario Museum 122 or even active
predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...
s,Peterson, O.A. (1909). A revision of Entelodontidae. Memoirs of the Carnegie Museum, 9:41-158 based on wear grooves on their dentition. By studying well-preserved fossils, JoeckelJoeckel, R.M. (1990). A functional interpretation of the masticatory system and paleoecology of Entelodonts. Paleobiology, vol. 16:4, p.459-482 re-evaluated these interpretations and performed several modeled analyses regarding the wear patterns on the dentition and structure of the skull (in particular the growth series and muscle reconstruction of the skull) and concluded an omnivorous diet for ''Archeaotherium'', and most likely ''Brachyhyops'', in which scavenging and active hunting appears to have played a possible role.


Paleoecology

The habitat in which ''Brachyhyops'' occurred appears to be savannah-woodland or open grassland and lived alongside a diversity of other herbivores and carnivores in Eocene Asia and western North America.Scott, W.B. (1945). The Mammalia of the Duchesne River Oligocene. Transactions of the American Philosophical Society, New Series, 34(3): 209-253Rasmussen, T.D., Hamblin, A.H., Tabrum, A.R. (1999). The Mammals of the Eocene Duchesne River Formation. In Gillette, D.D. (ed.) Vertebrate Paleontology in Utah. Miscellaneous Publication 99-1, Utah Geological Survey. Pp. 421-427


References

{{Taxonbar, from=Q4953455 Entelodonts Eocene Artiodactyla Extinct mammals of Asia Fossil taxa described in 1937 Prehistoric Artiodactyla genera