White River Fauna

Gomphotherium (; "nail beast" for its double set of straight tusks) is an extinct genus of gomphothere proboscidean from the Neogene of Eurasia, Africa and North America. It is the most diverse genus of gomphothere, with over a dozen valid species. The genus is probably paraphyletic, and ancestral to other gomphothere genera.

Hyaenodon ("hyena-tooth") is an extinct genus of carnivorous placental mammals from the tribe Hyaenodontini, part of the subfamily Hyaenodontinae (which is within the family Hyaenodontidae), that belonged to the now extinct order Hyaenodonta. The genus was found lived in Eurasia and North America from the Middle Eocene to the Early Miocene, from 38 to 17 million years ago, existing for . Hyaenodon first evolved in Asia, probably evolving from Propterodon.

Mesohippus (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. Its shoulder height is estimated at 60 cm.

thumb|Daeodon shoshonensis life restoration thumb|Daeodon (Dinohyus) hollandi, complete skeleton from the Agate Fossil Beds National Monument|Agate Springs Fossil Quarry in Nebraska. See text for nomenclature history

Archaeotherium (, meaning "ancient beast") is an extinct genus of entelodont artiodactyl endemic to North America during the Eocene and Oligocene epochs (35–28 mya). Archaeotherium fossils are most common in the White River Formation of the Great Plains, but they have also been found in the John Day Basin of Oregon and the Trans-Pecos area of Texas. Archaeotherium's fossils come from North America, between the Priabonian and Rupelian stages of the Eocene and Oligocene (35–28 million years ago). Up to fifteen species of Archaeotherium have been identified, which are divided into three subgenera

Moropus (meaning "slow foot") is an extinct genus of large perissodactyl mammal in the chalicothere family. They were endemic to North America during the Miocene from ~20.4–13.6 Mya, existing for approximately . Moropus belonged to the schizotheriine subfamily of chalicotheres, and has the best fossil record of any member of this group; numbers of individuals, including complete skeletons, have been found. The type species of Moropus, M. distans, was named by Othniel Charles Marsh in 1877, alongside two other species, M. elatus and M. senex. Three more species have been named since. Others hav

Megacerops ("large-horned face") is an extinct genus of brontothere, an extinct group of rhinoceros-like browsers traditionally classified as relatives of horses. Megacerops was endemic to North America during the Late Eocene, during the Chadronian land mammal age.

river in Nebraska and South Dakota, United States

Dinictis is a genus of the Nimravidae, an extinct family of feliform mammalian carnivores, also known as "false saber-toothed cats". Assigned to the subfamily Nimravinae, Dinictis was endemic to North America from the Late Eocene to Early Oligocene epochs (35.7—29.5 million years ago), existing for about . Including supplementary materials

Parahippus ("near to horse"), is an extinct equid, a relative of modern horses, asses, and zebras. It lived from 24 to 17 million years ago, during the Miocene epoch. It was very similar to Miohippus, but slightly larger, at around tall, at the withers. Their fossils have been found in North America, primarily in the Great Plains region and Florida.

Hoplophoneus (Greek: "murder" (phonos), "weapon" (hoplo)) is an extinct genus of saber-toothed carnivoran belonging to the family Nimravidae, sometimes known as false saber-toothed cats. The titular member of the subfamily Hoplophoninae, it is closely related to nimravids such as Eusmilus and Nanosmilus. Hoplophoneus lived in North America and Asia during the Late Eocene to Early Oligocene epochs from 35.7 to 30.5 mya, existing for approximately . Including supplementary materials The genus currently consists of three named species: H. oharri, H. occidentalis, and H. primaveus.

Syndyoceras is a small extinct genus of Artiodactyla, of the family Protoceratidae, endemic to central North America from the Miocene epoch (23.1—18.5 Ma), existing for approximately .

thumb|Skeletal reconstruction of Hyracodon Hyracodon ('hyrax tooth') is an extinct genus of perissodactyl mammal from the White River Formation.

Palaeolagus ('ancient hare') is an extinct genus of lagomorph. Palaeolagus lived during the Eocene and Oligocene epochs of North America.

Palaeocastor ('ancient beaver') is an extinct genus of beavers that lived in the North American Badlands during the late Oligocene period to early Miocene, 29.5~18.5 million years ago. Palaeocastor was much smaller than modern beavers. There are several species including Palaeocastor fossor, Palaeocastor magnus, Palaeocastor wahlerti, and Palaeocastor peninsulatus. The animals first became known on grounds of their fossilized burrows, the "Devil's corkscrews." ==Biology== thumb|left|P. peninsulates|205x205px Some members of this genus made corkscrew-shaped burrows and tunnels. Like many early

Metamynodon is an extinct genus of 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 to the Middle Eocene. The various species were large, displaying a suit of semiaquatic adaptations more similar to those of the modern hippopotamus, despite their closer affinities with rhinoceroses.

Merycoidodon ("ruminating teeth") is an extinct genus of herbivorous artiodactyl of the family Merycoidodontidae, more popularly known by the name Oreodon ("hillock teeth"). It was endemic to North America during the Middle Eocene to Middle Miocene (46—16 mya) existing for approximately .

Subhyracodon (Latin: "below the genus Hyracodon") is an extinct genus of hornless rhinocerotids.

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 .

Trigonias (Greek: "triangular" (trigonos), "ias" [denotes possession]) is an extinct genus of rhinocerotid from the late Eocene (Chadronian) some 35 million years ago of North America.

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. armatum average around

Protapirus (Latin: "before" (pro), + Brazilian Indian: "tapir" (tapira)) is an extinct genus of tapir known from the Oligocene and Miocene of North America and Eurasia.

Cynodesmus ("dog link") is an extinct genus of omnivorous canine which inhabited North America during the Oligocene living from 33.3—-26.3 Ma and existed for approximately .

Protoceras ('first horn') is an extinct genus of Artiodactyla, of the family Protoceratidae, endemic to North America. It lived from the Oligocene to the Early Miocene 33.3—16.0 Ma, existing for approximately .

Daphoenus is an extinct genus of amphicyonids, a group colloquially known as "bear-dogs". It includes not just some of the best preserved material out of any amphicyonid, but also the earliest members of the family, first appearing in the middle Eocene and surviving into the Early Oligocene. The members of the genus are rather small compared to some of its later relatives, such as Amphicyon or Ysengrinia, ranging in size from comparable to a house cat to a small wolf. It was widely distributed across North America, with most of its remains being discovered in the White River Group of the Great

Megalictis (meaning "great weasel") is an extinct genus of large predatory mustelids that existed in North America during the "cat gap" from the Late Arikareean (Ar4) in the Miocene epoch. It is thought to have resembled a huge, jaguar-sized ferret, weighing up to .

Bathornithidae is an extinct family of birds from the Eocene to Miocene of North America. Part of Cariamiformes, they are related to the still extant seriemas and the extinct Phorusrhacidae. They were likely similar in habits, being terrestrial, long-legged predators, some of which attained massive sizes.

Blastomeryx is an extinct genus of musk deer endemic to North America. It lived during the Miocene epoch 20.4—10.3 mya, existing for approximately . There may be only one species, Blastomeryx gemmifer. == Description == Blastomeryx was long and looked like a modern chevrotain. Its canines were elongated into tusks which it probably used to uproot plants and fend off predators. While Blastomeryx (as well as modern musk deer) lacked antlers, a Middle Miocene species had bony knobs on its skull, which have been interpreted as incipient horns. Blastomeryx had a reduced radius and ulna, as well as

Bathornis ("tall bird") is an extinct genus of birds related to modern day seriemas, that lived in North America about 37–20 million years ago. Like the closely related and also extinct phorusrhacids, it was a flightless predator, occupying predatory niches in environments classically considered to be dominated by mammals. It was a highly diverse and successful genus, spanning a large number of species that occurred from the Priabonian Eocene to the Burdigalian Miocene epochs.

Merycoidodontoidea, previously known as "oreodonts" or "ruminating hogs," 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. "Oreodont" means "mountain teeth," referring to the appearance of the molars. Most merycoidodontoids were sheep-sized, though some genera grew to the s

thumb|left|Life restoration Leptictis is an extinct genus of leptictid non-placental eutherian mammal known from the Late Eocene to Early Oligocene of North America. The type species, L. haydeni, was named in 1868 by Joseph Leidy in honour of Ferdinand Vandeveer Hayden. L. dakotensis was also named by Leidy in 1868, but he originally named it as a separate genus, Ictops, which is now seen as the same animal as Lepticitis. Since then, six other species have been named.

Leptomeryx is an extinct genus of artiodactyl that lived in North America during the middle Eocene through early Miocene. One of the earliest ruminants, it belongs to the extinct family Leptomerycidae, which is related to today's chevrotains. Most fossils were found in the badlands of the Midwestern United States in sedimentary rocks of the White River Group, in the Brule and Chadron formations. Additional remains have been reported from southern Canada and Mexico. The genus was scientifically described in 1853 by Joseph Leidy and includes several species.

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) existing for approximately .

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 .

Ischyromys is an extinct genus of rodent from North America. thumb|left|Skull

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 (33.9—16.3 mya) and lived for approximately .

Mesocyon ("middle dog") is an extinct genus of the Hesperocyoninae subfamily of early canids native to North America. It lived from the Oligocene to Early Miocene, 30.3—20.3 Ma, existing for approximately . Fossils are known from Oregon, southern California and the northern Great Plains. It was roughly coyote-sized, and the first known canid to have a primarily meat-based diet.

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 .

Promerycochoerus ("Before Merycochoerus" or "Before Ruminating Hog") is an extinct genus of hippopotamus-like oreodont artiodactyl that lived in Central North America during the Early Miocene, 27.3—18.5 million years ago. thumb|left|Promerycochoerus superbus The 1 m (3 ft 4 in) long creature is thought to have been amphibious, as all species possessed an elongated, barrel-shaped body and short limbs that are typical adaptations found in semi-aquatic mammals. P. superbus had a long tapir-like face, while P. carrikeri had a short, somewhat pig-like face.

Hypertragulus is an extinct genus of hypertragulid ruminant endemic to North America. It lived from the Late Eocene to the Middle Miocene, living , existing for approximately .

Stylemys (meaning "pillar turtle") is the first fossil genus of dry land tortoise belonging to the order Testudines discovered in the United States. The genus lived in temperate to subtropical areas of North America, Europe, and Asia, based on fossil distribution. The genus was first described in 1851 by Joseph Leidy. The tortoise was common in the prehistoric Badlands, especially Nebraska and South Dakota. The species has also been found in the formations in and around Badlands National Park. Fossil fragments have also been found in the Palm Park Formation of New Mexico.

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 .

The Temnocyoninae are an extinct subfamily of medium-sized amphicyonids endemic to North America that lived during the Early Oligocene to Early Miocene about 30.8-20.43 million years ago (Mya) existing for around 10 million years.

Oligobunis is an extinct genus of mustelids, which existed during the Miocene epoch.

Pangurban is an extinct genus of the family Nimravidae (the false saber-toothed cats), endemic to North America during the Eocene epoch (40–37 mya). It contains a single species, Pangurban egiae. Occurring several million years before other named nimravids in North America, the discovery of this species suggests that hypercarnivores evolved and spread quickly after the warm middle Eocene.

Enhydrocyon is an extinct genus of bone crushing canid which inhabited North America during the Oligocene and Early Miocene, 30.8—20.4 Ma, existing for approximately .

Pliocyon is an extinct genus of amphicyonids which inhabited North America during the Middle Miocene 16.0—13.6 Ma, existing for approximately . Fossils have been uncovered in South Florida, Oregon, and western Nebraska.

Paracrax ("near curassow") is a genus of extinct North American flightless birds, possibly related to modern seriemas and the extinct terror birds. Part of Bathornithidae (though some analysis recover it as closer to the living seriemas instead, or possibly entirely out of Cariamiformes), it is a specialised member of this group, being cursorial carnivores much like their South American cousins, some species attaining massive sizes.