Merycoidodontoidea, sometimes called "oreodonts" or " ruminating hogs", is an extinct superfamily of

prehistoric Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use o ...

cud-chewing

artiodactyl The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poste ...

s with short faces and fang-like

canine teeth In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, or (in the context of the upper jaw) fangs, eye teeth, vampire teeth, or vampire fangs, are the relatively long, pointed teeth. They can appear more flattened however ...

. As their name implies, some of the better known forms were generally hog-like, and the group has traditionally been placed within the

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 in ...

(

pigs The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus ''Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus ...

peccaries A peccary (also javelina or skunk pig) is a medium-sized, pig-like hoofed mammal of the family Tayassuidae (New World pigs). They are found throughout Central and South America, Trinidad in the Caribbean, and in the southwestern area of No ...

and their ancestors), though some recent work suggests they may have been more closely related to

camel A camel (from: la, camelus and grc-gre, κάμηλος (''kamēlos'') from Hebrew or Phoenician: גָמָל ''gāmāl''.) is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. ...

s.Spaulding, M., O'Leary, M.A. & Gatesy, J. (2009): Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution. '' PLoS ONE'' no 4(9): e7062.
article
/ref> "Oreodont" means "mountain teeth", referring to the appearance of the molars. Most oreodonts were sheep-sized, though some genera grew to the size of

cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...

. They were heavy-bodied, with short four-toed

hooves The hoof (plural: hooves) is the tip of a toe of an ungulate mammal, which is covered and strengthened with a thick and horny keratin covering. Artiodactyls are even-toed ungulates, species whose feet have an even number of digits, yet the rum ...

and comparatively long tails. The animals would have looked rather pig- or sheep-like, but features of their teeth indicate they were more closely related to

camelid 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, ...

s. They were most likely woodland and grassland browsers, and were widespread in North America during the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and 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 ...

and

Miocene The Miocene ( ) is the first 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 means "less recent" ...

. Later forms diversified to suit a range of different habitats. For example, '' Promerycochoerus'' had adaptations suggesting a semiamphibious lifestyle, similar to that of modern hippos.

Taxonomy

The two families of oreodonts are the Merycoidodontidae (originally known as Oreodontidae) which contains all of the advanced species, and the Agriochoeridae, smaller, primitive oreodonts. Together they form the now-extinct

suborder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

Oreodonta. Oreodonts may have been distantly related to

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 exta ...

es, and the pig-like

. Indeed, some scholars place Merycoidodontidae within the pig-related suborder

(Suiformes). Other scholars place oreodonts closer to

s in the suborder

Tylopoda Tylopoda (meaning "calloused foot") is a suborder of terrestrial herbivorous even-toed ungulates belonging to the order Artiodactyla. They are found in the wild in their native ranges of South America and Asia, while Australian feral camels are ...

. Still, other experts put the oreodonts together with the short-lived cainotheres in the taxonomic suborder Ancodonta comprising these two groups of extinct ancodonts. All scholars agree, however, that the oreodont was an early form of

even-toed ungulate The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing post ...

, belonging to the order Artiodactyla. Today, most evidence points towards the oreodonts being tylopods, along with camels, xiphodonts, and protoceratids. Over 50

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...

of Oreodonta have been described in the paleozoological literature. However, oreodonts are widely considered to be taxonomically oversplit, and many of these genera may prove to be synonymous. The last researchers to fully review oreodont taxonomy, C. Bertrand Schultz and Charles H. Falkenbach, have been criticized for erecting excessive numbers of genera, based in part on apparent anatomical differences between different specimens that were actually

taphonomic Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efrem ...

deformations due to postburial forces. Undeformed skulls would be placed in one genus, while skulls crushed from side to side would be placed in a second genus and skulls crushed from front to back would be placed in a third genus. Researchers are beginning to restudy oreodonts and synonymize many genera, but only a few groups have been reviewed.

Natural history

This diverse group of stocky prehistoric mammals grazed amid the

grassland A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur natur ...

prairie Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the ...

s, or

savanna A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to ...

s of

North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''no ...

and

Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...

throughout much of the

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...

era. First appearing 48 million years ago (Mya) during the warm

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

epoch of the

Paleogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago (Mya) to the beginning of ...

period, the oreodonts dominated the American landscape 34 to 23 Mya during the dry Oligocene epoch, but they mysteriously disappeared 4 Mya during the colder

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago (Mya) to the beginning of the present Quaternary Period Mya. ...

period. Today,

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

jaws and teeth of the Oreodonta are commonly found amid the 'Oreodon beds' (

White River Fauna The White River Fauna are fossil animals found in the White River Badlands of South Dakota, Wyoming, Colorado and Nebraska in the United States including Badlands National Park. The fossils have been found in the White River Formation, Chadron ...

) of the White River

badlands Badlands are a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded."Badlands" in '' Chambers's Encyclopædia''. London: George Newnes, 1961, Vol. 2, p. 47. They are characterized by steep slopes ...

South Dakota South Dakota (; Sioux language, Sioux: , ) is a U.S. state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota people, Lakota and Dakota peo ...

Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the so ...

Colorado Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

and

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the sou ...

. Many oreodont bones have also been reported at the

John Day Fossil Beds National Monument John Day Fossil Beds National Monument is a U.S. national monument in Wheeler and Grant counties in east-central Oregon. Located within the John Day River basin and managed by the National Park Service, the park is known for its well-preserved l ...

Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idah ...

. Some oreodonts have been found at

Agate Fossil Beds National Monument Agate Fossil Beds National Monument is a U.S. National Monument near Harrison, Nebraska. The main features of the monument are a valley of the Niobrara River and the fossils found on Carnegie Hill and University Hill. The area largely consist ...

. In Oligocene/Miocene

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, a ...

, oreodonts are surprisingly rare. Instead of the swarms found elsewhere, only six genera of oreodonts are known to have ranged there, and only one, ''

Mesoreodon ''Mesoreodon'' is an extinct genus of terrestrial herbivore of the family Merycoidodontidae, subfamily Merycoidodontinae (the oreodonts), endemic to North America during the Whitneyan stage of the Oligocene-Miocene epochs (33—20.6 mya) existi ...

'', is known from a single, good skeleton.

Lifestyle

The majority of oreodonts are presumed to have lived in herds, as suggested by the thousands of individuals in the various mass mortalities seen in the White River

Badlands Badlands are a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded."Badlands" in '' Chambers's Encyclopædia''. London: George Newnes, 1961, Vol. 2, p. 47. They are characterized by steep slopes ...

, Nebraska Oreodont beds, or

Chula Vista, California Chula Vista (; ) is the second-largest city in the San Diego metropolitan area, the seventh largest city in Southern California, the fifteenth largest city in the state of California, and the 78th-largest city in the United States. The popul ...

Diversity

Oreodonts underwent a huge diversification during the Oligocene and Miocene, adapting to a number of ecological niches, including: *Semiaquatic – hippo-like '' Promerycochoerus'' *Trunked browser – tapir-like '' Brachycrus'' *Large grazer – cow-sized ''

Eporeodon ''Eporeodon'' is an extinct genus of oreodont belonging to the family Merycoidontidae. It lived from the Oligocene epoch 30.8—24.8 mya) existing for approximately . Description The species of the genus are among the largest members of the fa ...

'' *Medium grazer – goat-like '' Merycoidodon'' *Small desert herbivore – goat- to cat-sized '' Sespia'' *Medium desert herbivore – ''

'' and the ubiquitous ''

Leptauchenia ''Leptauchenia'' is an extinct goat-like genus of terrestrial herbivore belonging to the oreodont family Merycoidodontidae, and the type genus of the tribe Leptaucheniini. The genus was endemic to North America during the Late Oligocene to Earl ...

Classification

The family Merycoidodontidae is divided into eleven

subfamilies In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

, with four genera not included in any subfamily (''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'') because they are either regarded as basal oreodonts, or their status within the family remains uncertain. *Family †Merycoidodontidae **subfamily ''incertae sedis'' ***†''

Aclistomycter ''Aclistomycter'' is an extinct genus of oreodont. It lived during the early Chadronian subepoch 37.2—33.9 mya, existing for approximately . from the Chambers Tuff Formation near Adobe Springs in Presidio County, Texas. ''Aclistomycter'' was ...

'' ***†'' Merychyus'' ***†'' Pseudogenetochoerus'' ***†'' Pseudoleptauchenia'' **Subfamily † Oreonetinae ***†'' Bathygenys'' ***†'' Megabathygenys'' ***†'' Oreonetes'' **Subfamily † Leptaucheniinae ***Tribe †

Leptaucheniini ''Leptauchenia'' is an extinct goat-like genus of terrestrial herbivore belonging to the oreodont family Merycoidodontidae, and the type genus of the tribe Leptaucheniini. The genus was endemic to North America during the Late Oligocene to Earl ...

****†''

Limnenetes ''Limnenetes'' is an extinct genus of oreodont, endemic to North America. They lived during the Late Eocene 37.2—33.9 mya, existing for approximately . Fossils have been uncovered in Montana and Texas. ''Limnenetes'' was a herbivore A ...

'' ****†''

'' ***Tribe † Sespiini ****†'' Sespia'' **Subfamily † Merycoidodontinae (syn. Oreodontinae) ***†'' Merycoidodon'' (syn. ''Blickohyus'', ''Genetochoerus'', ''Oreodon'', ''Otionohyus'', ''Paramerycoidodon'', ''Prodesmatochoerus'', ''Promesoreodon'', ''Subdesmatochoerus'') ***†''

'' **Subfamily † Miniochoerinae ***†''

Miniochoerus ''Miniochoerus'' is an extinct genus of small oreodont endemic to North America. They lived during the Late Eocene to Early Oligocene 38–30.8 mya, existing for approximately . Fossils have been found only in North Dakota, South Dakota, Nebrask ...

'' (syn. ''Paraminiochoerus'', ''Parastenopsochoerus'', ''Platyochoerus'', ''Pseudostenopsochoerus'', ''Stenopsochoerus'') **Subfamily † Desmatochoerinae ***†''

Desmatochoerus ''Desmatochoerus'' is a large extinct genus of oreodont of the family Merycoidodontidae, endemic to North America. They lived during the Late Oligocene to Middle Miocene 28.4—16.0 mya Mya may refer to: Brands and product names * Mya (prog ...

'' ***†''

'' ***†'' Megoreodon'' **Subfamily † Promerycochoerinae ***†'' Promerycochoerus'' ***†'' Merycoides'' **Subfamily † Merychyinae ***†''

Oreodontoides ''Oreodontoides'' is an extinct genus of oreodont of the family Merycoidodontidae endemic to North America. It lived during the Late Oligocene to Early Miocene (24.8—20.4 mya), existing for approximately . Fossils have been uncovered throughou ...

'' ***†''

Paroreodon ''Paroreodon'' is an extinct genus of oreodont of the family Merycoidodontidae, subfamily Merycoidodontinae, endemic to North America during the Oligocene-Miocene subepochs (30.8—20.6 mya), existing for approximately . Taxonomy ''Paroreodon'' ...

'' ***†'' Merycoides'' ***†'' Merychyus'' **Subfamily † Eporeodontinae ***†'' Dayohyus'' (syn. ''Eucrotaphus'' deemed ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...

'') ***†''

'' **Subfamily † Phenacocoelinae ***†''

Phenacocoelus ''Phenacocoelus'' is an extinct genus of oreodont of the family Merycoidodontidae, endemic to North America. They lived during the Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene Epoch made up of t ...

'' ***†'' Hypsiops'' **Subfamily † Ticholeptinae ***†''

Mediochoerus ''Mediochoerus'' is an extinct genus of oreodont of the family Merycoidodontidae, subfamily Merycoidodontinae, endemic to North America during the Early Miocene-Middle Miocene The Middle Miocene is a sub-epoch of the Miocene Epoch made up of ...

'' ***†''

Ticholeptus ''Ticholeptus'' is an extinct genus of oreodont endemic to North America during the Middle Miocene epochs (16.0—13.6 mya), existing for approximately . Fossils have been uncovered throughout the U.S. from Florida to Oregon, as well as Californ ...

'' ***†''Ustatochoerus'' **Subfamily † Merycochoerinae ***†'' Merycochoerus'' ***†'' Brachycrus'' In Lander (1998) the classification of Oreodontoidea was as follows: * Family Agriochoeridae Leidy, 1869 (syn. Artionychidae, Eomerycidae, Protoreodontidae) ** Subfamily Agriochoerinae Gill, 1872 (syn. Diplobunopsinae) *** ''Agriochoerus'' Leidy, 1850b (syn. ''Agriomeryx'', ''Artionyx'', ''Coloreodon'', ''Diplobunops'', ''Eomeryx'', ''Merycopater'') *** "Agriochoerus" maximus (Douglass, 1901) ** Subfamily Protoreodontinae Scott, 1890 *** ''Protoreodon'' Scott and Osborn, 1887 (syn. ''Agriotherium'', ''Chorotherium'', ''Hyomeryx'', ''Mesagriochoerus'', ''Protagriochoerus'') *** "Protoreodon" petersoni (Gazin, 1955) *** "Agriochoerus" minimus (Douglass, 1901) *** "Agriochoerus" transmontanus (Stock, 1949) * Family Merycoidodontidae ** Subfamily Bathygeniinae Lander, 1998 *** ''Bathygenys'' Douglass, 1901 (syn. ''Megabathygenys'', ''Parabathygenys'') ** Subfamily Aclistomycterinae Lander, 1998 *** ''Aclistomycter'' Wilson, 1971 ** Subfamily Leptaucheniinae Schultz and Falkenbach, 1940 *** ''Leptauchenia'' Leidy, 1856 (syn. ''Brachymeryx'', ''Cyclopidius'', ''Hadroleptauchenia'', ''Limnenetes'', ''Pithecistes'', ''Pseudocyclopidius'', ''Pseudoleptauchenia'') *** ''Sespia'' Stock, 1930 (syn. ''Megasespia'') ** Subfamily Miniochoerinae Schultz and Falkenbach, 1956 (syn. Oreonetinae, ?Cotylopinae, ?Merycoidodontinae, ?Oreodontinae) ** Subfamily Eucrotaphinae Lander, 1998 ** Subfamily Merycochoerinae Schultz and Falkenbach, 1940 (syn. Desmatochoerinae, Eporeodontinae, Promerycochoerinae) ** Subfamily Phenacocoelinae Schultz and Falkenbach, 1950 ** Subfamily Ticholeptinae Schultz and Falkenbach, 1941 (syn. Merychyinae)

References

{{Taxonbar, from=Q134697 Mammal superfamilies Miocene extinctions White River Fauna Eocene first appearances Tylopoda