Merycoidodontoidea

Merycoidodontoidea; Temporal range: 35–5 Ma PreꞒ Ꞓ O S D C P T J K Pg N Late Eocene to Miocene
	Reconstructions of various Miocene oreodonts, including Merycochoerus , Promerycochoerus , and Brachycrus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Suborder:	Tylopoda
Superfamily:	† Merycoidodontoidea
Families
	†Agriochoeridae ; †Merycoidodontidae †Oreonetinae ; †Leptaucheniinae ; †Merycoidodontinae ; †Miniochoerinae ; †Desmatochoerinae ; †Promerycochoerinae ; †Merychyinae ; †Eporeodontinae ; †Phenacocoelinae ; †Ticholeptinae ; †Merycochoerinae ; ;

Last updated February 28, 2024

Merycoidodontoidea, previously known as "oreodonts" or " ruminating hogs,"^{[ citation needed ]} are an extinct superfamily of prehistoric cud-chewing artiodactyls with short faces and fang-like canine teeth. As their name implies, some of the better known forms were generally hog-like, and the group has traditionally been placed within the Suina (pigs, peccaries and their ancestors), though some recent work suggests they may have been more closely related to camels.^[2] "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. They were heavy-bodied, with short four-toed hooves 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 camelids. They were most likely woodland and grassland browsers, and were widespread in North America during the Oligocene and Miocene. 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.^[1]

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 Oreodonta. Oreodonts may have been distantly related to pigs, hippopotamuses, and the pig-like peccaries. Indeed, some scholars^{[ who? ]} place Merycoidodontidae within the pig-related suborder Suina (Suiformes). Other scholars^{[ who? ]} place oreodonts closer to camels in the suborder Tylopoda. Still, other experts^{[ who? ]} 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, belonging to the order Artiodactyla. Today, most evidence points towards the oreodonts being tylopods, along with camels, xiphodonts, and protoceratids.^{[ citation needed ]}

Over 50 genera of Oreodonta have been described in the paleozoological literature. However, oreodonts are widely considered to be taxonomically oversplit,^[3]^[4] 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,^[5] have been criticized for erecting excessive numbers of genera, based in part on apparent anatomical differences between different specimens that were actually taphonomic deformations due to postburial forces.^[3] 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 as of 2004^[update] only a few groups had been reviewed.^[3]^[6]^[7]

Natural history

This diverse group of stocky prehistoric mammals grazed amid the grasslands, prairies, or savannas of North and Central America throughout much of the Cenozoic era. First appearing 48 million years ago (Mya) during the warm Eocene epoch of the Paleogene 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 epoch of the late Neogene period.^{[ citation needed ]}

Today, fossil jaws and teeth of the Oreodonta are commonly found amid the 'Oreodon beds' (White River Fauna) of the White River badlands in South Dakota, Nebraska, Colorado and Wyoming. Many oreodont bones have also been reported at the John Day Fossil Beds National Monument in Oregon. Some oreodonts have been found at Agate Fossil Beds National Monument. In Oligocene/Miocene Florida, 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 , 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, Nebraska Oreodont beds, or Chula Vista, California.^{[ citation needed ]}

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
Medium grazer – goat-like Merycoidodon
Small desert herbivore – goat- to cat-sized Sespia
Medium desert herbivore – Mesoreodon and the ubiquitous Leptauchenia

Classification

The family Merycoidodontidae is divided into eleven subfamilies, with four genera not included in any subfamily ( incertae sedis ) because they are either regarded as basal oreodonts, or their status within the family remains uncertain.

Family †Merycoidodontidae
- subfamily incertae sedis
  - † Aclistomycter
  - † Merychyus
  - † Pseudogenetochoerus
  - † Pseudoleptauchenia
- Subfamily †Oreonetinae
  - † Bathygenys
  - † Megabathygenys
  - † Oreonetes
- Subfamily †Leptaucheniinae ^[6]
  - Tribe †Leptaucheniini
    - † Limnenetes
    - † Leptauchenia
  - Tribe †Sespiini
    - † Sespia
- Subfamily †Merycoidodontinae (syn. Oreodontinae)^[3]
  - † Merycoidodon (syn. Blickohyus, Genetochoerus, Oreodon, Otionohyus, Paramerycoidodon, Prodesmatochoerus, Promesoreodon, Subdesmatochoerus)
  - † Mesoreodon
- Subfamily †Miniochoerinae ^[3]
  - † Miniochoerus (syn. Paraminiochoerus, Parastenopsochoerus, Platyochoerus, Pseudostenopsochoerus, Stenopsochoerus)
- Subfamily †Desmatochoerinae
  - † Desmatochoerus
  - † Eporeodon
  - † Megoreodon
- Subfamily †Promerycochoerinae
  - † Promerycochoerus
  - † Merycoides
- Subfamily †Merychyinae
  - † Oreodontoides
  - † Paroreodon
  - † Merycoides
  - † Merychyus
- Subfamily †Eporeodontinae
  - † Dayohyus (syn. Eucrotaphus deemed nomen dubium )
  - † Eporeodon
- Subfamily †Phenacocoelinae
  - † Phenacocoelus
  - † Hypsiops
- Subfamily †Ticholeptinae
  - † Mediochoerus
  - † Ticholeptus
  - †Ustatochoerus
- Subfamily †Merycochoerinae
  - † Merycochoerus
  - † Brachycrus

In Lander (1998) the classification of Oreodontoidea was as follows:^[4]

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)

Related Research Articles

Artiodactyls are mammals belonging to the order Artiodactyla. Typically, they are ungulates which bear weight equally on two of their five toes: the third and fourth, often in the form of a hoof. The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, most perissodactyls bear weight on an odd number of the five toes. Another difference between the two is that many artiodactyls digest plant cellulose in one or more stomach chambers rather than in their intestine as perissodactyls do. The advent of molecular biology, along with new fossil discoveries, found that cetaceans fall within this taxonomic branch, being most closely related to hippopotamuses. Some modern taxonomists thus apply the name Cetartiodactyla to this group, while others opt to include cetaceans within the existing name of Artiodactyla. Some researchers use "even-toed ungulates" to exclude cetaceans and only include terrestrial artiodactyls, making the term paraphyletic in nature.

Entelodontidae is an extinct family of pig-like artiodactyls which inhabited the Northern Hemisphere from the late Eocene to the Middle Miocene epochs, about 38-19 million years ago. Their large heads, low snouts, narrow gait, and proposed omnivorous diet inspires comparisons to suids and tayassuids (peccaries), and historically they have been considered closely related to these families purely on a morphological basis. However, studies which combine morphological and molecular (genetic) data on artiodactyls instead suggest that entelodonts are cetancodontamorphs, more closely related to hippos and cetaceans through their resemblance to Pakicetus, than to basal pigs like Kubanochoerus and other ungulates.

Merycoidodon is an extinct genus of herbivorous artiodactyl of the family Merycoidodontidae, more popularly known by the name Oreodon. It was endemic to North America during the Middle Eocene to Middle Miocene existing for approximately 30 million years.

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 Mountain uplift, which cuts southwest–northeast through the Horse Heaven mining district northeast of Madras. Aside from the Picture Gorge district, which defines the type, the formation is visible on the surface in two other areas: another exposure is in the Warm Springs district west of the uplift, between it and the Cascade Range, and the third is along the south side of the Ochoco Mountains. All three exposures, consisting mainly of tuffaceous sediments and pyroclastic rock rich in silica, lie unconformably between the older rocks of the Clarno Formation below and Columbia River basalts above.

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 6 million years.

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 7 million years. Fossils have been found only in North Dakota, South Dakota, Nebraska, Montana, and Wyoming.

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 Early Miocene and lived for approximately 17.6 million years.

Leptaucheniinae was a taxon of small, goat-like oreodonts with proportionally big heads found throughout North America during the Late Oligocene. Because skeletons of Leptauchenia and Sespia have been found by the literal thousands, they are often quoted as being the most numerous fossil mammals in North America during the Late Oligocene. They had high-crowned, hypsodont teeth which were used to chew gritty vegetation.

Cormocyon is an extinct genus of borophagine canid native to North America. It lived from the Oligocene to the Early Miocene, 30.8—20.6 Mya, existing for about 10.2 million years. It is regarded as a primitive, transitional member of the Borophagini tribe.

The Daphoeninae are an extinct subfamily of dog-like, terrestrial carnivores, which belonged to the family Amphicyonidae of the suborder Caniformia. The group inhabited North America from the Middle Eocene subepoch to the Middle Miocene subepoch 42—15.97 million years ago (Mya), existing for about 26.03 million years.

Merychyus is an extinct genus of oreodont of the family Merycoidodontidae, endemic to North America. It lived during the Miocene, 20.4—10.3 mya, existing for approximately 10 million years. Fossils are widespread through the central and western United States.

Merycochoerus is an extinct genus of oreodont of the family Merycoidodontidae, endemic to North America. They lived during the Early Oligocene 33.9—30.8 mya, existing for approximately 3 million years. Fossils are widespread through the western United States.

Oreonetes is an extinct genus of oreodont endemic to North America from the Late Eocene 38.0—33.9 Ma living approximately 4.1 million years.

Merycoides is an extinct genus of oreodont of the subfamily Merycoidodontinae endemic to North America. It lived during the Oligocene to Late Miocene, 30.8—16.0 mya, existing for approximately 15 million years. Fossils have been uncovered throughout the western U.S. as well as Florida.

Paroreodon is an extinct genus of oreodont of the family Merycoidodontidae, subfamily Merycoidodontinae, endemic to North America during the Oligocene-Miocene subepochs, existing for approximately 10.2 million years.

Mediochoerus is an extinct genus of oreodont of the family Merycoidodontidae, subfamily Merycoidodontinae, endemic to North America during the Early Miocene-Middle Miocene subepochs, existing for approximately 7 million years.

Agriochoerus is an extinct genus of scansorial herbivore of the tylopod family Agriochoeridae, endemic to North America. Agriochoerus and other agriochoerids possessed claws, which is rare within Artiodactyla, as well as likely being scansorial. Agriochoerus was first described in 1869.

Ustatochoerus is an extinct genus of oreodont of the family Merycoidodontidae, endemic to North America. It lived during the late Oligocene to Miocene, 24–10.3 mya, existing for approximately 14 mya. Fossils are widespread through the central and western United States.

The Nimravinae are a subfamily of the Nimravidae, an extinct family of feliform mammalian carnivores sometimes known as false saber-toothed cats. They were endemic to North America, Europe, and Asia from the Middle Eocene through the Late Miocene epochs, spanning about 33.2 million years. Centered in North America, the radiation of the Nimravinae from the Eocene to Oligocene was the first radiation of cat-like carnivorans.

The Marsland Formation is a geologic formation in Nebraska. It preserves fossils dating back to the Neogene period.

References

1 2 Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. pp. 270–271. ISBN 1-84028-152-9.
↑ 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. doi : 10.1371/journal.pone.0007062 article
1 2 3 4 5 Stevens, M.S.; Stevens, J.B. (1996). "Merycoidodontinae and Miniochoerinae". In Prothero, D.R.; Emry, R.J. (eds.). The terrestrial Eocene-Oligocene transition in North America. Cambridge: Cambridge University Press. pp. 498–573. ISBN 0-521-43387-8.
1 2 Lander, B. (1998). "Oreodontoidea". In Janis, C.M.; Scott, K.M.; Jacobs, L.L. (eds.). Evolution of Tertiary mammals of North America. Cambridge: Cambridge University Press. pp. 402–425. ISBN 0-521-35519-2.
↑ Schultz, C.B. & C.H. Falkenbach (1968). "The phylogeny of the oreodonts: parts 1 and 2". Bulletin of the American Museum of Natural History. 139: 1–498. hdl:2246/1992.
1 2 CoBabe, E.A. (1996). "Leptaucheniinae". In Prothero, D.R.; Emry, R.J. (eds.). The terrestrial Eocene-Oligocene transition in North America. Cambridge: Cambridge University Press. pp. 574–580. ISBN 0-521-43387-8.
↑ Hoffman, J.M. & D.R. Prothero (2004). "Revision of the late Oligocene dwarfed leptauchenine oreodont Sespia (Mammalia: Artiodactyla)". Bulletin of the New Mexico Museum of Natural History and Science. 26: 155–164.

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[EoDP-1] 1 2 Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. pp. 270–271. ISBN 1-84028-152-9.

[2] 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. doi : 10.1371/journal.pone.0007062 article

[Ste&Ste-3] 1 2 3 4 5 Stevens, M.S.; Stevens, J.B. (1996). "Merycoidodontinae and Miniochoerinae". In Prothero, D.R.; Emry, R.J. (eds.). The terrestrial Eocene-Oligocene transition in North America. Cambridge: Cambridge University Press. pp. 498–573. ISBN 0-521-43387-8.

[Lander98-4] 1 2 Lander, B. (1998). "Oreodontoidea". In Janis, C.M.; Scott, K.M.; Jacobs, L.L. (eds.). Evolution of Tertiary mammals of North America. Cambridge: Cambridge University Press. pp. 402–425. ISBN 0-521-35519-2.

[SchFal68-5] Schultz, C.B. & C.H. Falkenbach (1968). "The phylogeny of the oreodonts: parts 1 and 2". Bulletin of the American Museum of Natural History. 139: 1–498. hdl:2246/1992.

[CoBabe-6] 1 2 CoBabe, E.A. (1996). "Leptaucheniinae". In Prothero, D.R.; Emry, R.J. (eds.). The terrestrial Eocene-Oligocene transition in North America. Cambridge: Cambridge University Press. pp. 574–580. ISBN 0-521-43387-8.

[HofPro04-7] Hoffman, J.M. & D.R. Prothero (2004). "Revision of the late Oligocene dwarfed leptauchenine oreodont Sespia (Mammalia: Artiodactyla)". Bulletin of the New Mexico Museum of Natural History and Science. 26: 155–164.

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