Archaeotherium Mortoni 01
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''Archaeotherium'' (, meaning "ancient beast") is an extinct
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
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 ...
endemic to
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
during the
Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
and
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 ...
epochs (35–28 mya). ''Archaeotherium'' fossils are most common in the
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 ...
of the
Great Plains The Great Plains is a broad expanse of plain, flatland in North America. The region stretches east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. They are the western part of the Interior Plains, which include th ...
, but they have also been found in the John Day Basin of
Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...
and the
Trans-Pecos The Trans-Pecos, as originally defined in 1887 by the Texas geologist Robert T. Hill, is the distinct portion of Texas that lies west of the Pecos River. The term is considered synonymous with Far West Texas, a subdivision of West Texas. The Tran ...
area of
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 ...
. ''Archaeotherium'''s fossils come from North America, between the
Priabonian The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene Epoch or Series. It spans the time between . The Priabonian is preceded by the Bartonian and is followed by the Rupelian, the lowest stage ...
and
Rupelian The Rupelian is, in the geologic timescale, the older of two age (geology), ages or the lower of two stage (stratigraphy), stages of the Oligocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between . It is preceded b ...
stages of the
Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
and
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 ...
(35–28 million years ago). Up to fifteen species of ''Archaeotherium'' have been identified, which are divided into three
subgenera In biology, a subgenus ( subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the ge ...
. One contains the type species, ''A. mortoni'', among others; another contains very large taxa formerly named ''Megachoerus'' and ''Pelonax''; and the last contains ''A. calkinsi''. ''Archaeotherium'' was distinguished from most entelodonts by having an unusually long snout and large
jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...
flanges, extensions of the
zygomatic arch In anatomy, the zygomatic arch (colloquially known as the cheek bone), is a part of the skull formed by the zygomatic process of temporal bone, zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the ...
es that are characteristic of the group. The latter may be the result of sexual dimorphism or species differentiation. Healed bite marks on several ''Archaeotherium'' specimens suggest that it engaged in facial biting behaviours, similar to dromedary camels, and their faces consequently may have had thickened skin for protection. ''Archaeotherium'' had powerful neck muscles, which were supported by a bony hump comprising the first six
thoracic vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebra (anatomy), vertebrae of intermediate size between the ce ...
. Its digits were unfused, capable of spreading, and may have supported a fleshy pad, enabling it to move more effectively on soft terrain. Like other entelodonts, it had large incisors and canines, triangular
premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...
s, and small,
bunodont The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone tooth ...
molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...
. ''Archaeotherium'' species varied in size, with ''A. mortoni'' having a skull length of , and ''A. zygomaticus'' having a skull length of . ''Archaeotherium'' is thought to have been
omnivorous 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 ...
, and exhibited strong adaptations for
carnivory A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...
. Fossils of the early
camelid Camelids are members of the biological family (biology), family Camelidae, the only currently living family in the suborder Tylopoda. The seven extant taxon, extant members of this group are: dromedary, dromedary camels, Bactrian camels, wild Bac ...
''
Poebrotherium ''Poebrotherium'' ( ) is an extinct genus of camelid, endemic to North America. They lived from the Eocene to Miocene epochs, 46.3—13.6 mya, existing for approximately . Discovery and history ''Poebrotherium'' was first named by scientist J ...
'' bearing entelodont bite marks indicate that ''Archaeotherium'' cached food, consuming the front half and saving the rear half to eat later. It was incapable of slicing meat due to its bunodont molars, and compensated for this by using its head and neck muscles together to rip off chunks of flesh. ''Archaeotherium'' mostly inhabited
woodland A woodland () is, in the broad sense, land covered with woody plants (trees and shrubs), or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunli ...
s and open plains, though occasionally associated with
riparian A riparian zone or riparian area is the interface between land and a river or stream. In some regions, the terms riparian woodland, riparian forest, riparian buffer zone, riparian corridor, and riparian strip are used to characterize a ripar ...
environments.


Taxonomy


Early history

In 1850, Alexander Culbertson collected several fossils from the area around
Fort Laramie Fort Laramie (; founded as Fort William and known for a while as Fort John) was a significant 19th-century trading post, diplomatic site, and military installation located at the confluence of the Laramie and the North Platte Rivers. They joi ...
, Wyoming. His father, Joseph, presented them to the
Academy of Natural Sciences of Philadelphia The Academy of Natural Sciences of Drexel University, formerly the Academy of Natural Sciences of Philadelphia, is the oldest natural science research institution and museum in the Americas. It was founded in 1812, by many of the leading natur ...
. Two of the fossils were named by anatomist and palaeontologist
Joseph Leidy Joseph Mellick Leidy (September 9, 1823 – April 30, 1891) was an American paleontologist, parasitologist and anatomist. Leidy was professor of anatomy at the University of Pennsylvania, later becoming a professor of natural history at Swarth ...
. One of them was a small skull fragment, preserving the third and fourth left
premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...
s. It was determined to be a new species, and was designated the holotype of a new taxon, ''Archaeotherium mortoni''. Its generic name derives from the Greek αρχαιο ("ancient") and θήριον ("beast"). The
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
, ''A. mortoni'', was named after
Samuel George Morton Samuel George Morton (January 26, 1799 – May 15, 1851) was an American physician, natural scientist, and writer. As one of the early figures of scientific racism, he argued against monogenism, the single creation story of the Bible, instead sup ...
, then the president of the
Academy of Natural Sciences of Philadelphia The Academy of Natural Sciences of Drexel University, formerly the Academy of Natural Sciences of Philadelphia, is the oldest natural science research institution and museum in the Americas. It was founded in 1812, by many of the leading natur ...
. Several more complete specimens were described in an 1853 paper, also by Leidy: a fragment of a mature specimen's skull, preserving in their entirety the two front
molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...
and parts of the last molar and last
premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...
, all on both sides; and the rear of a young individual's skull, broken in two and missing the upper left half of the skull (including the
zygomatic arch In anatomy, the zygomatic arch (colloquially known as the cheek bone), is a part of the skull formed by the zygomatic process of temporal bone, zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the ...
). Though perplexed by the anatomy it displayed, Leidy suggested that it was related to ''
Entelodon magnus ''Entelodon'' (meaning 'complete teeth', from Ancient Greek ''entelēs'' 'complete' and ''odōn'' 'tooth', referring to its "complete" eutherian dentition), formerly called ''Elotherium'', is an extinct genus of entelodont artiodactyl endemic t ...
'' from Eurasia, if it did not represent the same taxon outright. In 1873,
Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of paleontology. A prolific fossil collector, Marsh was one of the preeminent paleontologists of the nineteenth century. Among his legacies are the discovery or ...
named a new species of ''Elotherium'' (now ''Entelodon''), ''E. crassum'', based on remains found in Colorado. Shortly thereafter, Edward Drinker Cope named another new species, ''Elotherium ramosum''. Subsequently, he reassigned both ''E. crassum'' and ''E. ramosum'' to a genus of their own, ''Pelonax''. In 1951, James Reid MacDonald lumped ''Pelonax'' into ''Archaeotherium'', though opted to retain it as a subgenus. In 2007, Scott Foss fully synonymised ''Pelonax'' with ''Archaeotherium''. In 1920, geologist Edward Leffingwell Troxell described a new entelodont genus, ''Megachoerus'', as part of a series of papers discussing Marsh's entelodontid collection. In that paper, he designated ''M. zygomaticus'' as the type species. A second species, ''M. latidens'', was also assigned. In 2007, Scott Foss synonymised ''Megachoerus'' with ''Archaeotherium''. In the same series of papers that named ''Megachoerus'', Troxell named the new taxon "''Choerodon" calkinsi'', for remains formerly assigned to ''
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 ...
'' and ''Elotherium''; however, ''Choerodon'' is
preoccupied In biology, a homonym is a name for a taxon that is identical in spelling to another such name, that belongs to a different taxon. The rule in the International Code of Zoological Nomenclature is that the first such name to be published is the s ...
by a genus of
wrasse The wrasses are a family, Labridae, of marine ray-finned fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 81 genera, which are divided into nine subgroups or tribes. They are typically small, ...
. ''C. calkinsi'' is now regarded as a species of ''Archaeotherium'', and may represent part of its own subgenus. In 1922,
William John Sinclair William John Sinclair (1877–1935) was a geologist and vertebrate paleontologist, noteworthy for his collaboration with Walter W. Granger on stratigraphy in New Mexico and Wyoming. Sinclair received in 1904 his M.S. and Ph.D. from U. C. Berkel ...
erected the new taxon ''Scaptohyus altidens'', based on a partial skull,
mandible 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 ...
s, and several bone fragments recovered from the Corral Draw locality of South Dakota in 1893 by R. E. Zuver. The species name, ''altidens'', is in reference to the height of the third lower premolar. By 2007, ''Scaptohyus'' was regarded as a
junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...
of ''Archaeotherium''. In 1935,
Erich Maren Schlaikjer Erich Maren Schlaikjer ( ; November 22, 1905 in Newtown, Ohio – November 5, 1972) was an American geologist and dinosaur hunter. Assisting Barnum Brown, he co-described ''Pachycephalosaurus'' and what is now ''Montanoceratops''. Other discoveri ...
named ''Dinohyus'' (now ''Daeodon'') ''minimus'', based on the symphyseal region of a juvenile's lower jaw. After comparisons with ''A. trippensis'', ''D. minimus'' was reassigned to ''Archaeotherium'' in 1998. It may be the same taxon as ''A. trippensis''.


Proposed synonymy with ''Entelodon''

As far back as 1853, Joseph Leidy, the describer of ''Archaeotherium'', suggested that it may have been part of the same genus as ''Entelodon magnus''. In 1857, he reassigned ''Archaeotherium mortoni'' to the genus ''Elotherium'' without comment under the binomial name ''Elotherium imperator''. A posthumous paper by
Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...
, published in 1915, listed the same taxon as ''Entelodon imperator''. In a 1909 revision of Entelodontidae, Olaf August Peterson resurrected ''Archaeotherium'' as a genus. He suggested that ''Archaeotherium'' and ''Entelodon'' could be distinguished by geography, as the former was North American and the latter was Eurasian. In 1940,
William Berryman Scott William Berryman Scott (February 12, 1858 – March 29, 1947) was an American vertebrate paleontologist, authority on mammals, and principal author of the White River Oligocene monographs. He was a professor of geology and paleontology at Pr ...
and
Glenn Lowell Jepsen Glenn Lowell "Jep" Jepsen (4 March 1903 – 15 October 1974) was an American paleontologist and professor of vertebrate paleontology at Princeton University. He collected and described many fossil species particularly from the Oligocene of the Badla ...
noted strong similarities between the two genera, though they stopped short of synonymising them due to the incompleteness of the latter. In 1979, the relationship between the two genera was re-examined by French palaeontologist
Michel Brunet Michel Brunet may refer to: * Michel Brunet (historian) (1917–1985), Canadian historian * Michel Brunet (paleontologist) Michel Brunet (born April 6, 1940) is a French paleontologist and a professor at the Collège de France between 2008 and 20 ...
. He contended that the differences between ''Archaeotherium'' and ''Entelodon'' were insufficient, and that the two genera should be synonymised; in this case, ''Entelodon'', being named earlier, would take priority. This total synonymy has not been followed by subsequent authors, though Scott Foss noted that it remained a topic for investigation.


Inner systematics

Many species have been assigned to ''Archaeotherium'' over the years. In 2007, Foss divided ''Archaeotherium'' into three subgenera: ''Archaeotherium'' proper, subgenus A, and subgenus B. Subgenus A consists predominantly of very large species formerly referred to as ''Megachoerus'' and ''Pelonax'', whereas Subgenus B consists of ''A. calkinsi'', a species known from a single specimen from the John Day Formation of Oregon that has features of both ''Archaeotherium'' and ''Daeodon''. Foss suggested the possibility of elevating them to genus level, though did not do so in that work. A list of species according to work of Foss is as follows: An additional species, "A." ''coarctatum'', was formerly assigned to ''Archaeotherium''. In 2007, it was assigned to a new genus, '' Cypretherium''.


Classification

''Archaeotherium'' belongs 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 ...
, a family whose exact taxonomic position has long been disputed. Similarities to members of
Suina Suina (also known as Suiformes) is a suborder of omnivorous, non- ruminant artiodactyl mammals that includes the domestic pig and peccaries. A member of this clade is known as a suine. Suina includes the family Suidae, termed suids, known ...
were recognised as far back as 1853.
Henri Marie Ducrotay de Blainville Henri Marie Ducrotay de Blainville (; 12 September 1777 – 1 May 1850) was a French zoologist and anatomist. Life Blainville was born at Arques-la-Bataille, Arques, near Dieppe, Seine-Maritime, Dieppe. As a young man, he went to Paris to study a ...
is said to have suspected that the genus belonged to a
carnivora Carnivora ( ) is an order of placental mammals specialized primarily in eating flesh, whose members are formally referred to as carnivorans. The order Carnivora is the sixth largest order of mammals, comprising at least 279 species. Carnivor ...
n family he dubbed Subursi, based on characters now understood to be convergent.
Karl Alfred von Zittel Karl Alfred Ritter von Zittel (25 September 1839 – 5 January 1904) was a German palaeontologist best known for his ''Handbuch der Palaeontologie'' (1876–1880). Biography Karl Alfred von Zittel was born in Bahlingen in the Grand Duchy ...
believed that ''Archaeotherium'' was a true suid, placing it within the subfamily
Achaenodon ''Achaenodon'' is an extinct artiodactyl mammal belonging to the family Helohyidae. It lived in the mid-late Eocene (about 43-39 million years ago) and its fossil remains have been found in North America. Description ''Achaenodon'' was around th ...
tinae.
William Berryman Scott William Berryman Scott (February 12, 1858 – March 29, 1947) was an American vertebrate paleontologist, authority on mammals, and principal author of the White River Oligocene monographs. He was a professor of geology and paleontology at Pr ...
, in 1940, concurred that it was a relative of ''Achaenodon'', though placed it within "Palaeodonta". This interpretation would be followed by authors who did not regard them as suiforms, and instead preferred to associate them with cebochoerids, choeropotamids, and helohyids. In 1955, Charles Lewis Gazin suggested that entelodonts were offshoots of Helohyinae (within a greater
Dichobunidae Dichobunidae is an extinct family of basal artiodactyl mammals from the early Eocene to late Oligocene of North America, Europe, and Asia. The Dichobunidae include some of the earliest known artiodactyls, such as ''Diacodexis''. Description T ...
), if not direct descendants of ''Helohyus'' proper. Since then, entelodontids have mostly been regarded as close relatives of
Suidae Suidae is a family (biology), family of Even-toed ungulate, artiodactyl mammals which are commonly called pigs, hogs, or swine. In addition to numerous fossil species, 18 Extant taxon, extant species are currently recognized (or 19 counting domes ...
(pigs) within Suina/Suiformes. More recent
phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...
, such as that of Yu ''et al.''. (2023), diverge from the classical suiform model. Instead, they suggest that the family lies close to ''
Andrewsarchus ''Andrewsarchus'' (), meaning "Roy Chapman Andrews, Andrews' ruler", is an extinct genus of artiodactyl that lived during the Eocene, Middle Eocene in what is now China. The genus was species description, first described by Henry Fairfield Osb ...
'',
anthracotheres Anthracotheriidae is a paraphyletic family of extinct, hippopotamus-like artiodactyl ungulates related to hippopotamuses and whales. The oldest genus, '' Elomeryx'', first appeared during the middle Eocene in Asia. They thrived in Africa and Eura ...
, hippopotamuses and whales, within
Cetancodontamorpha Cetancodontamorpha is a total clade of artiodactyls defined, according to Spaulding ''et al''., as Whippomorpha "plus all extinct taxa more closely related to extant members of Whippomorpha than to any other living species". Whippomorpha is th ...
. Below is a reproduction of the Yu ''et al.''. cladogram of Cetancodontamorpha:In 1996, Spencer G. Lucas and Robert J. Emry suggested that ''Archaeotherium'' represented the terminal stage of a North American entelodont clade, which became extinct and was subsequently replaced by an Asian clade (itself ending with ''
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 ...
'') which entered North America near the end of the Oligocene. In 2007, Scott Foss instead proposed that ''Archaeotherium'' represents a late stage of a continuous North American lineage, beginning with ''
Brachyhyops ''Brachyhyops'' is an extinct genus of entelodont artiodactyl mammal that lived during the Eocene Epoch of western North America and southeastern Asia (including Mongolia, China, and Kazakhstan).Colbert, E.H. (1937). Notice of a new genus and spe ...
'' and terminating in ''Daeodon.'' Conversely, Yu ''et al.''. (2023) recovered ''Archaeotherium'' as belonging to a
polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tree ...
with ''Brachyhyops'' and a clade consisting of ''Entelodon'' and ''
Paraentelodon ''Paraentelodon'' is an extinct entelodont from the Late Oligocene of Asia. The fossils of the type species ''P. intermedium'' were found in Georgia, Kazakhstan and China. An indeterminate species represents in Bugti Hills which is the late Oli ...
''.


Description


Size

The many species assigned to ''Archaeotherium'' differ dramatically in size. The type species, ''A. mortoni'', is relatively small and slender, estimated to have weighed around and a skull length, measured condylobasally, (from the tip of the
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...
to the back of the
occipital condyles The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the Atlas (anatomy), atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape ...
) of about . The larger species, those formerly known as ''Megachoerus'', were considerably larger. ''A. zygomaticus'' had a skull length of around . ''A. calkinsi'' in particular is noted as being robust beyond what is observed in other entelodonts. The largest species of ''Archaeotherium'' was ''A. trippensis''.


Skull

The skull length of ''Archaeotherium mortoni'', is about 27% of the total head–body length, based on the partly restored skeleton of SDSM 3346: this is 8% smaller, proportionally, than in ''
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 ...
''.Joeckel, R. M.
A Functional Interpretation of the Masticatory System and Paleoecology of Entelodonts
''Paleobiology'' 16, no. 4 (1990): 459-82.
The genus ''Archaeotherium'' is characterised by having a particularly elongated face and prominent
jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...
flanges. These were extensions of the
zygomatic arch In anatomy, the zygomatic arch (colloquially known as the cheek bone), is a part of the skull formed by the zygomatic process of temporal bone, zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the ...
es, analogous to those of
hippopotamus The hippopotamus (''Hippopotamus amphibius;'' ; : hippopotamuses), often shortened to hippo (: hippos), further qualified as the common hippopotamus, Nile hippopotamus and river hippopotamus, is a large semiaquatic mammal native to sub-Sahar ...
es. The
jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...
has a lightly developed posterior process that does not form a buttress on the front margin of the
glenoid cavity The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from , "socket", reflecting the shoulder joint's ball-and-socket form. It is a shallow, pyri ...
. The ''Archaeotherium'' specimens initially assigned to "''Megachoerus''" and "''Pelonax''" bear massively enlarged jugal flanges, and a combination of a deep jaw and knob-like mandibular tubercles, respectively. The
orbits In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...
(eye sockets) were forward-facing and fully enclosed by a
postorbital bar The postorbital bar (or postorbital bone) is a bony arched structure that connects the frontal bone of the skull to the zygomatic arch, which runs laterally around the eye socket. It is a trait that only occurs in mammalian taxa, such as most strep ...
. Unusually among entelodonts (with the exception of ''Brachyhyops''), ''Archaeotherium'''s pterygoids bore a midline
synarthrosis A synarthrosis is a type of joint which allows no movement under normal conditions. Sutures and gomphoses are both synarthroses. Joints which allow more movement are called amphiarthroses or diarthroses. Syndesmoses are considered to be amph ...
, meaning they were essentially incapable of movement. This was likely an adaptation to resisting stresses exerted on the back of the skull by the jaw muscles. The
articular surface A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...
of ''Archaeotherium'''s dentary
condyle A condyle (;Entry "condyle"
in
is comparable in orientation to that of modern
carnivora Carnivora ( ) is an order of placental mammals specialized primarily in eating flesh, whose members are formally referred to as carnivorans. The order Carnivora is the sixth largest order of mammals, comprising at least 279 species. Carnivor ...
ns. As such, it may have been able to open its jaws to a maximum gape of 109°. The
sagittal crest A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are excepti ...
and
temporal fossa The temporal fossa is a fossa (shallow depression) on the side of the skull bounded by the temporal lines above, and the zygomatic arch below. Its floor is formed by the outer surfaces of four bones of the skull. The fossa is filled by the te ...
e of entelodonts like ''Archaeotherium'' were very large, further indicating a strong bite force.


Dentition

Entelodonts such as ''Archaeotherium'' had the same general tooth morphology: large
incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
s and canines, triangular premolars, and small, bunodont molars. They possessed the typical
placental Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished ...
dental formula of . The first and second
incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
s of ''Archaeotherium mortoni'' are relatively large, procumbent, and well-spaced. The canines are long and pointed. Together, the canines and incisors formed an effective device for grasping and puncturing. There are slight gaps between the premolars (
diastema A diastema (: diastemata, from Greek , 'space') is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition may be referred to ...
ta), unlike in ''Daeodon''. The
premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...
s are transversely compressed, with high, pointed crowns. The third premolar is narrower than the fourth, and is convex labially. It is double rooted, has a single cusp, and only has slight posterior cingulum. The fourth premolar is triple-routed and described as cuboidal in shape. The third molar lacks a
hypocone A cusp is a pointed, projecting, or elevated feature. In animals, it is usually used to refer to raised points on the crowns of teeth. The concept is also used with regard to the leaflets of the four heart valves. The mitral valve, which has ...
. No
sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...
is observed in the dentition.


Postcrania

''Archaeotherium'''s postcranial elements were similar to those of other entelodonts. The neck had seven
caudal vertebrae Caudal vertebrae are the vertebrae of the tail in many vertebrates. In birds, the last few caudal vertebrae fuse into the pygostyle, and in apes, including humans, the caudal vertebrae are fused into the coccyx. In many reptiles, some of the caud ...
. It was short and massive, and accommodated strong muscles. These were further supported by a bony ridge, spanning the first six
thoracic vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebra (anatomy), vertebrae of intermediate size between the ce ...
, which likely formed a large hump in life. ''Archaeotherium'' had only two
sacral vertebrae The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...
. The
caudal vertebrae Caudal vertebrae are the vertebrae of the tail in many vertebrates. In birds, the last few caudal vertebrae fuse into the pygostyle, and in apes, including humans, the caudal vertebrae are fused into the coccyx. In many reptiles, some of the caud ...
are unusual among artiodactyls, most closely resembling those of
giraffe The giraffe is a large Fauna of Africa, African even-toed ungulate, hoofed mammal belonging to the genus ''Giraffa.'' It is the Largest mammals#Even-toed Ungulates (Artiodactyla), tallest living terrestrial animal and the largest ruminant on ...
s among the group. The ribs were surprisingly lightly built for such a large animal. The forelimbs were elongate, with a high and slender
scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...
and a massively constructed humerus. The feet were functionally didactyl (having two weight-bearing digits). Like most artiodactyls, they exhibited paraxony, distributing weight equally over the third and fourth digits. The digits were unfused like those of
camelids Camelids are members of the biological family Camelidae, the only currently living family in the suborder Tylopoda. The seven extant members of this group are: dromedary camels, Bactrian camels, wild Bactrian camels, llamas, alpacas, vicuñas, ...
, and the toes could spread;CLIFFORD, ANDREW B.
THE EVOLUTION OF THE UNGULIGRADE MANUS IN ARTIODACTYLS
''Journal of Vertebrate Paleontology'', vol. 30, no. 6, 2010, pp. 1827–1839. ''JSTOR'', .
this, in conjunction with hypothetical foot pads, may have helped ''Archaeotherium'' move on soft terrain. Unlike the humerus, the
femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...
was long and relatively slender, whereas the
tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...
was shorter and more robust; the
fibula The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...
is very much reduced, though is not co-ossified.


Palaeobiology


Intraspecific interactions

Young ''Archaeotherium'' had fairly small
temporalis In anatomy, the temporalis muscle, also known as the temporal muscle, is one of the muscles of mastication (chewing). It is a broad, fan-shaped convergent muscle on each side of the head that fills the temporal fossa, superior to the zygomatic ...
muscles, which increased in size as the animal matured. This suggests that, as in other entelodontids, the jugal flanges and strong jaws of the genus were involved in adult social interactions over obtaining and processing food. Further, the jugal flanges of ''Archaeotherium'' differ in shape and size among specimens. Some interpret this as evidence of
sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...
,Foss, S. E., 2001, Systematics and paleobiology of the Entelodontidae (Mammalia, Artiodactyla)
h.D. dissertation Hilda Doolittle (September 10, 1886 – September 27, 1961) was an American modernist poet, novelist, and memoirist who wrote under the name H.D. throughout her life. Her career began in 1911 after she moved to London and co-founded th ...
Dekalb, Northern Illinois University, 222 p.
whilst others interpret it as evidence of intraspecies variation. Assuming the former, it is similar to that seen in
giant forest hog The giant forest hog (''Hylochoerus meinertzhageni''), the only member of its genus (''Hylochoerus''), is native to wooded habitats in Africa and is one of the largest wild members of the pig family, Suidae, along with a few subspecies of the wi ...
s. Thus, it can be reasonably assumed that ''Archaeotherium'''s jugals supported large preorbital glands used for chemical communication, signalling readiness for mating. Healed bite-marks on the frontals,
lacrimals The lacrimal bones are two small and fragile bones of the facial skeleton; they are roughly the size of the little fingernail and situated at the front part of the medial wall of the orbit. They each have two surfaces and four borders. Several bon ...
and
maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...
e, as well as an ''A. scotti'' specimen with a damaged left cheek flange, suggest that at least some ''Archaeotherium'' populations engaged in
agonistic An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the agoni ...
facial biting. In such confrontations, one animal may have attempted to fit the head of the other in its mouth and bite down with the canines and incisors, similar to modern dromedary camels. The anterior tubercles of entelodonts such as ''Archaeotherium'' may have supported toughened skin, which would act as a buffer during such interactions.


Feeding and diet

Like other entelodonts, ''Archaeotherium'' is generally seen as a mixed feeder, with an inclination towards carnivory. The type species, ''A. mortoni'', bore specialisations for biting and chewing resistant objects, such as hard fruits, stems, and bones. The jaws were enormously strong and operated largely by chopping, though exhibited enough lateral movement for the molars to grind objects. ''Archaeotherium'''s teeth show signs of uneven wear, indicating that it often favoured chewing on one side of the jaw. Unlike ''Daeodon'', the teeth do not exhibit so-called "piecrust fractures". This suggests that, whereas ''Daeodon'' was more specialised for the consumption of large carcasses, ''Archaeotherium'' was not. Tooth wear patterns suggest that its front teeth were often used to strip leaves from plants, though there is a lack of soil scratches that would indicate rooting in the ground. Scott Foss, in 2001, interpreted this as the result of feeding on plants such as
liana A liana is a long-Plant stem, stemmed Woody plant, woody vine that is rooted in the soil at ground level and uses trees, as well as other means of vertical support, to climb up to the Canopy (biology), canopy in search of direct sunlight. T ...
s. ''Archaeotherium'''s dentition was incapable of slicing meat, like most extant mammalian predators: rather, it compensated using its strong neck musculature, using its head and neck together to tear off chunks of flesh. Fossil evidence suggests that in North America they may sometimes have hunted the early camelid ''
Poebrotherium ''Poebrotherium'' ( ) is an extinct genus of camelid, endemic to North America. They lived from the Eocene to Miocene epochs, 46.3—13.6 mya, existing for approximately . Discovery and history ''Poebrotherium'' was first named by scientist J ...
''. Bite marks on the cervical vertebrae of the camels suggest that ''Archaeotherium'' ran alongside its prey while hunting, delivering crushing a bite to the neck and the back of the skull. The prey animal's body was then severed in half, and the rear section was consumed. The front half was stockpiled in a food cache to be consumed later.


Brain and senses

Endocast An endocast is the internal cast of a hollow object, often referring to the cranial vault in the study of brain development in humans and other organisms. Endocasts can be artificially made for examining the properties of a hollow, inaccessible ...
s of ''Archaeotherium'''s skull suggest that the brain was very small. The
cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...
was small, short and narrow, and the
cerebral hemisphere The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres ...
s were proportionally very small. However, the
olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OF ...
s were relatively large, indicating that ''Archaeotherium'' had a keen sense of smell.


Palaeoecology

''Archaeotherium'' lived from the
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 ...
to the
Arikareean The Arikareean North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 30,600,000 to 20,800,000 years BP, a period of . It is usuall ...
North American Land Mammal Ages The North American land mammal ages (NALMA) establishes a geologic timescale for North American fauna beginning during the Late Cretaceous and continuing through to the present. These periods are referred to as ages or intervals (or stages when ref ...
(NNLMAs). The earliest occurrences of the genus are from the
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 ...
of the
White River Group 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, Badlands ...
. Specimens have been recovered from the
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 ...
,
John Day Formation The John Day Formation is a series of rock strata exposed in the Picture Gorge district of the John Day River basin and elsewhere in north-central Oregon in the United States. The Picture Gorge exposure lies east of the Blue Mountains (Oregon), ...
,
Brule Formation The Brule Formation was deposited between 34 and 30 million years ago, roughly the Rupelian age (Oligocene). It occurs as a subunit of the White River Group in South Dakota, Nebraska, Colorado, North Dakota, and Wyoming. It is a sequence of fin ...
and
Chadron Formation Chadron Formation is a rock formation in North Dakota, South Dakota, northwestern Nebraska, and eastern Wyoming. It is named after the town of Chadron, Nebraska Chadron ( ) is a city in and the county seat of Dawes County, Nebraska, United St ...
, as well as from the
Trans-Pecos The Trans-Pecos, as originally defined in 1887 by the Texas geologist Robert T. Hill, is the distinct portion of Texas that lies west of the Pecos River. The term is considered synonymous with Far West Texas, a subdivision of West Texas. The Tran ...
area of
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 ...
. The latest known occurrence of the genus comes from the Turtle Butte Formation, which bears fossils of ''A. trippensis''; the Turtle Butte represents either the late Oligocene or the early Miocene.


Palaeoenvironment

The White River Formation, from which many ''Archaeotherium'' fossils are known, extends from the
Upper Eocene 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') an ...
to the
Middle Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene 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 define the epoch are well identified but t ...
. Based on
palaeosol In geoscience, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The definition of the term in geology and paleontology is slightly different from its use in soil science. In geology and paleon ...
analysis, the lower levels of the White River Formation represent a forested environment with a high
water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...
, dominated by
taproot A taproot is a large, central, and dominant root from which other roots sprout laterally. Typically a taproot is somewhat straight and very thick, is tapering in shape, and grows directly downward. In some plants, such as the carrot, the taproot ...
-bearing
dicotyledon The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, ...
s. The upper levels, however, represent an open, sparsely vegetated plain. It is believed that this environmental shift reflects global drying trends across the Eocene–Oligocene boundary. The depositional environments of the
Brule Formation The Brule Formation was deposited between 34 and 30 million years ago, roughly the Rupelian age (Oligocene). It occurs as a subunit of the White River Group in South Dakota, Nebraska, Colorado, North Dakota, and Wyoming. It is a sequence of fin ...
, also part of the White River Group, are believed to have been a
gallery forest A gallery forest is one formed as a corridor along rivers or wetlands, projecting into landscapes that are otherwise only sparsely treed such as savannas, grasslands, or deserts. The gallery forest maintains a more temperate microclimate above th ...
and a wooded grassland, populated at least in part by hackberry trees (''
Celtis ''Celtis'' is a genus of about 60–70 species of deciduous trees, commonly known as hackberries or nettle trees, in the hemp family Cannabaceae. It has a cosmopolitan distribution. Description ''Celtis'' species are generally medium-sized tree ...
''). The John Day Formation underwent a similar transformation to the White River Formation: the mid-Eocene Clarno Nuts Beds flora was tropical, while early Oligocene Slanting Leaf Beds held mostly temperate, deciduous taxa. Examples were maples ('' Acer''), plane trees (''
Platanus ''Platanus'' ( ) is a genus consisting of a small number of tree species native to the Northern Hemisphere. They are the sole living members of the family Platanaceae. All mature members of ''Platanus'' are tall, reaching in height. The type ...
''), and oaks, (''
Quercus An oak is a hardwood tree or shrub in the genus ''Quercus'' of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisp ...
''), along with an extinct member of the
avocado The avocado, alligator pear or avocado pear (''Persea americana'') is an evergreen tree in the laurel family (Lauraceae). It is native to Americas, the Americas and was first domesticated in Mesoamerica more than 5,000 years ago. It was priz ...
family ('' Cinnamomophyllum''). Smaller representatives of the late John Day Formation's fauna were soapberries (''
Dipteronia ''Dipteronia'' is a genus with two living and one extinct species in the soapberry family Sapindaceae. The living species are native to central and southern China. The fossil species has been found in Middle Paleocene to Early Oligocene sediments ...
''), roses (''
Rosa Rosa or De Rosa may refer to: Plants and animals * ''Rosa'' (plant), the genus of roses * Rosa (sea otter), a sea otter that has become popular on the internet * Rosa (cow), a Spanish-born cow People * Rosa (given name) * Rosa (surname) * San ...
''), and the evergreen shrub genus ''
Mahonia ''Mahonia'' is a formerly accepted genus of approximately 70 species of shrubs or, rarely, small trees with evergreen leaves in the family Berberidaceae, native to eastern Asia, the Himalaya, North America, and Central America. They are closely ...
''. ''Archaeotherium'' is known to have inhabited all of these formations, preferring woodlands and open plains, though may have frequented
riparian A riparian zone or riparian area is the interface between land and a river or stream. In some regions, the terms riparian woodland, riparian forest, riparian buffer zone, riparian corridor, and riparian strip are used to characterize a ripar ...
habitats. ''Archaeotherium'' is known from the White River Group (including the
Brule Formation The Brule Formation was deposited between 34 and 30 million years ago, roughly the Rupelian age (Oligocene). It occurs as a subunit of the White River Group in South Dakota, Nebraska, Colorado, North Dakota, and Wyoming. It is a sequence of fin ...
and
Chadron Formation Chadron Formation is a rock formation in North Dakota, South Dakota, northwestern Nebraska, and eastern Wyoming. It is named after the town of Chadron, Nebraska Chadron ( ) is a city in and the county seat of Dawes County, Nebraska, United St ...
), and the John Day Formation. The Chadron Formation preserves taxa such as the
brontothere Brontotheriidae is a family of extinct mammals belonging to the order Perissodactyla, the order that includes horses, rhinoceroses, and tapirs. Superficially, they looked rather like rhinos with some developing bony nose horns, and were some of ...
''
Megacerops ''Megacerops'' ("large-horned face", from '' méga-'' "large" + '' kéras'' "horn" + '' ōps'' "face") is an extinct genus of the prehistoric odd-toed ungulate (hoofed mammal) family Brontotheriidae, an extinct group of rhinoceros-like browsers ...
'' and the hyaenodont ''
Hyaenodon ''Hyaenodon'' ("hyena-tooth") is an Extinction (biology), extinct genus of Carnivore, carnivorous Placentalia, placental mammals from extinct tribe Hyaenodontini within extinct subfamily Hyaenodontinae (in extinct Family (biology), family Hyaenod ...
''. The Orella Member of the Brule Formation, a subunit of the White River Group, bears the leptictid '' Leptictis'', the aforementioned ''Hyaenodon'', the nimravids '' Dinictis'' and ''
Hoplophoneus ''Hoplophoneus'' (Greek: "murder" (phonos), "weapon" (hoplo)) is an extinct genus of the family Nimravidae, lived in North America and Asia during the Late Eocene to Early Oligocene epochs from 35.7 to 30.5 mya, existing for approximately . Tax ...
'', the
amphicyonid Amphicyonidae is an extinct family of terrestrial carnivorans belonging to the suborder Caniformia. They first appeared in North America in the middle Eocene (around 45 mya), spread to Europe by the late Eocene (35 mya), and further spread to Asi ...
'' Daphoenus'', the
canid Canidae (; from Latin, ''canis'', "dog") is a family (biology), biological family of caniform carnivorans, constituting a clade. A member of this family is also called a canid (). The family includes three subfamily, subfamilies: the Caninae, a ...
'' Hesperocyon'', the perissodactyls ''
Hyracodon ''Hyracodon'' ('hyrax tooth') is an extinct genus of perissodactyl mammal. It was a lightly built, pony-like mammal of about 1.5 m (5 ft) long. ''Hyracodons skull was large in comparison to the rest of the body. ''Hyracodon's'' dentiti ...
'' and ''
Mesohippus ''Mesohippus'' (Greek language, Greek: / meaning "middle" and / meaning "horse") is an extinct genus of early horse. It lived 37 to 32 million years ago in the Early Oligocene. Like many fossil horses, ''Mesohippus'' was common in North America. ...
'' (plus an indeterminate
rhinocerotoid Rhinocerotoidea is a superfamily (taxonomy), superfamily of Perissodactyla, perissodactyls that appeared 56 million years ago in the Paleocene. They included four extinct families, the Amynodontidae, the Hyracodontidae, the Paraceratheriidae, an ...
), the merycoidodonts '' Merycoidodon'' and '' Miniochoerus'', the
camelid Camelids are members of the biological family (biology), family Camelidae, the only currently living family in the suborder Tylopoda. The seven extant taxon, extant members of this group are: dromedary, dromedary camels, Bactrian camels, wild Bac ...
''
Poebrotherium ''Poebrotherium'' ( ) is an extinct genus of camelid, endemic to North America. They lived from the Eocene to Miocene epochs, 46.3—13.6 mya, existing for approximately . Discovery and history ''Poebrotherium'' was first named by scientist J ...
'', the leptochoerid '' Stibartus'', the hypertragulid '' Hypertragulus'', the leptomerycid ''
Leptomeryx ''Leptomeryx'' is an extinct genus of ruminant of the family Leptomerycidae, endemic to North America during the Eocene through Oligocene 38–24.8 Mya, existing for approximately . It was a small deer-like ruminant with somewhat slender body. ...
'', and the rodents '' Ischyromys'' and '' Paradjidaumo''. The amynodont ''
Metamynodon ''Metamynodon'' is an extinct genus of Amynodontidae, amynodont that lived in North America (White River Fauna) and Asia from the late Eocene until early Oligocene, although the questionable inclusion of ''M. mckinneyi'' could extend their range ...
'' is known from certain parts of the Brule Formation. The Lower Blue Basin section of the John Day Formation preserves the
metatheria Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as wel ...
n ''
Herpetotherium ''Herpetotherium'' is an extinct genus of metatherian mammal, belonging to the possibly paraphyletic family Herpetotheriidae. Native to North America from the Eocene to Early Miocene, fossils have been found in California, Oregon, Texas, Florida, ...
'', the nimravids ''Dinictis'' and ''Hoplophoneus'', the amphicyonid ''
Temnocyon ''Temnocyon'' is an extinct genus of amphicyonids endemic to North America. It lived from the Oligocene to Early Miocene approximately 30.8—20.4 mya, existing for about . The first fossils are recorded in North America at Logan Butte in the ...
'', the canids ''
Archaeocyon ''Archaeocyon'' ("ancient dog") is an extinct genus of the Borophaginae subfamily of canids native to North America. It lived during the Oligocene epoch 32-24 Ma., existing for approximately . Species of ''Archaeocyon'' are among the earliest ...
'', '' Enhydrocyon'' and ''
Phlaocyon ''Phlaocyon'' (from Greek ''phlao'', "eat greedily" and ''cyon'', "dog") is an extinct genus of the Borophaginae subfamily of canids native to North America. It lives from the Early Oligocene to the Early Miocene epoch 33.3–16.3 Mya, existing ...
'', the equids ''
Mesohippus ''Mesohippus'' (Greek language, Greek: / meaning "middle" and / meaning "horse") is an extinct genus of early horse. It lived 37 to 32 million years ago in the Early Oligocene. Like many fossil horses, ''Mesohippus'' was common in North America. ...
'' and ''
Miohippus ''Miohippus'' (meaning "small horse") is an extinct genus of horse existing longer than most Equidae. It lived in what is now North America from 32 to 25 million years ago, during the late Eocene to late Oligocene. According to the Florida Museu ...
'', the
rhinocerotid A rhinoceros ( ; ; ; : rhinoceros or rhinoceroses), commonly abbreviated to rhino, is a member of any of the five extant taxon, extant species (or numerous extinct species) of odd-toed ungulates (perissodactyls) in the family (biology), famil ...
''
Diceratherium ''Diceratherium'' (meaning "two horned beast") is an extinct genus of rhinocerotid native to North America during the Oligocene through Miocene living from 33.9 to 11.6 mya, existing for approximately . Mass estimates for the type species, ''D. ...
'', the tayassuids '' Perchoerus'' and '' Thinohyus'', the merycoidodont '' Eporeodon'', the agriochoerid '' Agriochoerus'', the hypertragulid ''Hypertragulus'', and the rodent '' Haplomys'' (plus an indeterminate eomyid). The Turtle Butte Formation, from which the latest species (''A. trippensis'') is known, preserves the canids ''Enhydrocyon'' and ''
Leptocyon The genus ''Leptocyon'' (Greek: ''leptos'' slender + ''cyon'' dog) includes 11 species and was the first canine. They were small and weighed around . They first appeared in North America around 34 million years ago in the Oligocene, at the same ...
'', the nimravid ''Hoplophoneus'', the equid ''
Archaeohippus ''Archaeohippus'' (Greek: "ancient" (archaios), "horse" (hippos)) is an extinct three-toed member of the family Equidae known from fossils of early Oligocene to middle Miocene age. The genus is noted for several distinct skeletal features. The sk ...
'', the merycoidodonts '' Megoreodon'' and '' Paramerychyus'', and the camelid "Protomeryx" ('' Miotylopus'') ''leonardi''.


References

{{Taxonbar, from=Q519252 Entelodonts Eocene Artiodactyla Oligocene Artiodactyla Eocene genus first appearances Eocene mammals of North America Oligocene mammals of North America Rupelian genus extinctions White River Fauna Fossil taxa described in 1850 Prehistoric Artiodactyla genera