The White River Fauna are fossil animals found in the White River Group of South Dakota, North Dakota, Wyoming, Colorado and Nebraska in the United States. In southwest South Dakota and northwest Nebraska, these fossils are characteristic of the White River Badlands (including Badlands National Park), though they can be found far beyond the limits of the White River watershed.
In Wyoming, the White River Group is undifferentiated, and is more commonly known as the White River Formation. Further east in Nebraska and South Dakota, the group is divided into the Chadron Formation (lower part) and Brule Formation (upper part). Exposures are less well-investigated in northeast Colorado and scattered sites across western North Dakota. The White River Group is overlain by the Sharps Formation in Badlands National Park and the Arikaree Group in northwest Nebraska.
Animals from the White River Group date from the Eocene and Oligocene epochs. The fauna is representative of four North American Land Mammal Ages (NALMAs):
Arikareean (late Oligocene [Chattian] - early Miocene [Burdigalian], 29.5 - 18.5 million years ago) Whitneyan ("mid-Oligocene" [Rupelian], 31.8 - 29.5 million years ago) Orellan (early Oligocene [Rupelian], 33.9 - 31.8 million years ago) Chadronian (late Eocene [Priabonian], 37 - 33.9 million years ago) Only the uppermost layers of the White River Group extend into the Arikareean (specifically, the informal "brown siltstone member" of the Brule Formation). All NALMA and Epoch information in this list refers solely to each species' distribution through the White River Group, as some species survive into later time intervals outside of the White River area.
Birds GenusSpeciesNALMAEpochNotesImage†Archaealectrornis†A. sibleyi"early Oligocene"A potential pheasant or guan-like bird†Badistornis†B. aramusOrellanearly OligoceneAn aramid (limpkin relative) known from both leg fossils and possible egg fossils.†Bathornis†B. celeripesChadronian - Orellanlate Eocene - early OligoceneThe type genus of Bathornithidae, an extinct family of large predatory birds related to seriemas.†B. cursorChadronianlate Eocene†B. geographicusWhitneyan"mid" Oligocene†B. veredus (type)Chadronian - Orellanlate Eocene - early OligoceneButeo†B. grangeriOrellanearly OligoceneA hawk in the living genus Buteo"Gavia"†"G." pusillaOrellanearly OligoceneA potential loon†Gnotornis†G. aramielusWhitneyan"mid" OligoceneA heron†Palaeogyps†P. prodromusChadronianlate EoceneA potential cathartid (New World vulture)†Palaeonossax†P. senectusWhitneyan"mid" OligoceneA potential cracid (guan or curassow relative)†Palaeoplancus†P. sternbergiWhitneyan"mid" OligoceneAn osprey-like accipitriform, initially regarded as an eagle†Paracrax†P. antiquaOrellanearly OligoceneA bathornithid initially mistaken for a cormorant (Phalacrocorax mediterraneus)†P. giganteaWhitneyan"mid" OligoceneA large bathornithid, closely related and similar to the conspecific Bathornis; however, it seems to have occupied more arid environments.†P. wetmoreiWhitneyan"mid" Oligocene†Phasmagyps†P. patritusChadronianlate EoceneA potential cathartid (New World vulture)†Procrax†P. brevipesChadronianlate EoceneA potential cracid (guan or curassow relative) with short legs similar to piping guans (Pipile)
Mammals
†Apatemyids GenusSpeciesNALMAEpochNotesImage†Apatemys†A. sp.ChadronianWilliam W. Korth, Clint A. Boyd, Jeff J. Person, and Deborah K. Anderson (2022). "Special Issue: Fossil mammals from ant mounds situated on exposures of the Big Cottonwood Creek Member of the Chadron Formation (latest Eocene-early Oligocene), Sioux County, Nebraska." Paludicola 13 (4).late EoceneAn apatemyid (part of an extinct group of aye-aye-like insectivores)†Sinclairella†S. dakotensisChadronian - Whitneyanlate Eocene - "mid" OligoceneAn apatemyid
Artiodactyls
†Antracotheres GenusSpeciesNALMAEpochNotesImage†Aepinacodon†A. americanusChadronianlate EoceneA large bothriodontine anthracothere (extinct hippo relative) with a long snout.†A. deflectus†Bothriodon†B. rostratusChadronian - Orellanlate Eocene - early OligoceneA medium-sized bothriodontine anthracothere with a very long snout.†Elomeryx†E. armatusOrellan - Whitneyanearly - "mid" OligoceneA small-medium bothriodontine anthracothere with a slender snout.†Heptacodon†H. curtus (type)Orellan - Whitneyanearly - "mid" OligoceneA medium-large anthracotheriine anthracothere with a short, broad snout.†H. gibbicepsWhitneyan"mid" Oligocene†H. occidentaleChadronian - Orellanlate Eocene - early Oligocene
Camelids GenusSpeciesNALMAEpochNotesImage†MatthewlabisA camelid which appears to be a long-snouted relative of Poebrotherium.†Poebrotherium †P. wilsoni (type) †P. chadronensis †P. eximium †P. franki †P. labratumAn early camelid (camel and llama relative) with a lithe, antelope-like build†PseudolabisAn early stenomyline (small gazelle-like camelid)
†Entelodonts GenusSpeciesNALMAEpochNotesImage†Archaeotherium†A. mortoniChadronian - Whitneyanlate Eocene - "mid" OligoceneA medium-sized entelodont (extinct boar-like omnivores related to hippos).
†Leptochoerids Leptochoerids are an extinct and rare group of hoofed mammals. Their affinities and anatomy are nearly unknown beyond their teeth, which were generally bunodont in form. GenusSpeciesNALMAEpochNotesImage†Leptochoerus†L. elegansChadronian - Whitneyanlate Eocene - "mid" OligoceneA leptochoerid with a fairly broad snout and teeth which were slightly more adapted for grinding compared to Stibarus.†L. emilyaeOrellanearly Oligocene†L. spectabilisOrellan - Whitneyanearly - "mid" Oligocene†L. supremusWhitneyan"mid" Oligocene†Stibarus†S. obtusilobusChadronian - Whitneyanlate Eocene - "mid" OligoceneA leptochoerid with a narrower snout and teeth which were slightly more adapted for shearing compared to Leptochoerus†S. quadricuspisChadronian - Orellanlate Eocene - early Oligocene
†Merycoidodontoids Merycoidodontoids, also known as oreodonts, are an extinct yet formerly abundant group of hoofed mammals with short legs and barrel-shaped bodies. Most oreodonts were part of the family Merycoidodontidae, distinguished by hoofs and a short tail. Despite their pig-like stature, they were probably more closely related to camels. GenusSpeciesNALMAEpochNotesImage†Agriochoerus†A. antiquusChadronian - Orellanlate Eocene - early OligoceneAn agriochoerid (an early-diverging merycoidodontoid which retains claws and a long tail)†A. majorOrellanearly Oligocene†A. gaudryiWhitneyan"mid" Oligocene†Bathygenys†B. alphaChadronianlate EoceneA small oreonetine, one of the smallest and earliest known oreodeonts. An index taxon of the Chadronian NALMA.†B. hedlundaeChadronianlate Eocene†Leptauchenia†L. decoraOrellan - Whitneyanearly - "mid" EoceneA small leptaucheniine with a short skull and adaptations for an abrasive diet. Abundant during the Whitneyan.†L. majorWhitneyan"mid" OligoceneA small leptaucheniine with a short skull and adaptations for an abrasive diet. The main index taxon of the Whitneyan NALMA.†Merycoidodon†M. bullatusOrellan 4 - Whitneyanearly - "mid" EoceneA common sheep-sized merycoidodontine. The main index taxon of the Orellan 4.†M. culbertsoniChadronian 4 - Orellanlate Eocene - early OligoceneA common sheep-sized merycoidodontine†M. majorlate Whitneyan"mid" OligoceneA common sheep-sized merycoidodontine. The main index taxon of the late Whitneyan.†M. presidioensisChadronian 2late EoceneA common sheep-sized merycoidodontine†Mesoreodon†M. chelonyxArikareeanlate OligoceneA merycoidodontine, probably the ancestor to the later oreodont subfamily Promerycochoerinae.†Miniochoerus†M. affinisOrellan 2early OligoceneA small miniochoerine. The main index taxon of the Orellan 2.†M. chadronensisChadronian 4 - Orellan 1late Eocene - early OligoceneA medium-sized miniochoerine. The main index taxon of the Chadronian 4.†M. forsythaeChadronian 3late EoceneA medium-sized early miniochoerine.†M. gracilisOrellan 3early OligoceneA very small miniochoerine. The main index taxon of the Orellan 3.†M. starkensisOrellan 4early OligoceneA small miniochoerine.
†Protoceratids †Protoceratidae is an extinct family of deer-like hoofed mammals which would evolve elaborate horns during the Miocene. The Eocene-Oligocene species found in the White River Group were rare and had simpler skulls compared to their later (synthetoceratine) counterparts. GenusSpeciesNALMAEpochNotesImage†Heteromeryx†H. disparChadronianearly EoceneA "leptotraguline" (early-diverging protoceratid without horns)†"Leptotragulus"†"L." profectusChadronianearly EoceneA "leptotraguline", sometimes regarded as a species of Trigenicus.†Poabromylus†P. sp.Chadronianearly EoceneA "leptotraguline"†Protoceras†P. celerWhitneyan"mid" OligoceneA protoceratine (early horned protoceratid) with strong sexual dimorphism. The males have large canines and three pairs of blunt horns similar to giraffe ossicones.†Pseudoprotoceras†P. longinarisChadronianearly EoceneA "leptotraguline"†P. minorChadronianearly EoceneA "leptotraguline", sometimes regarded as a species of Poabromylus.†P. tayloriChadronianearly EoceneA "leptotraguline"
Ruminants Early ruminants (cud-chewing hoofed mammals) of the White River Group were very small. They were similar in appearance to modern chevrotains (mouse deer) or hornless dik-diks, though beyond this general body shape their affinities are unclear. GenusSpeciesNALMAEpochNotesImage†Hypertragulus†H. calcaratusOrellan - Whitneyanearly - "mid" OligoceneA small fruit-eating hypertragulid which may have lived in groups. The main index taxon of the Orellan NALMA.†Hypisodus†H. minimusChadronian - Whitneyanlate Eocene - "mid" OligoceneA tiny (rabbit-sized) hypertragulid with enlarged eyes, a thin snout, and hypsodont teeth. One of the smallest artiodactyls to ever exist.†H. retallackiWhitneyan"mid" Oligocene†Leptomeryx†L. evansiOrellan - Whitneyanearly - "mid" OligoceneA leptomerycid, the most common species found in the area. An index taxon of the Orellan NALMA.†L. exilisOrellanearly OligoceneA leptomerycid†L. obliquidensWhitneyan"mid" OligoceneA leptomerycid†L. speciosusChadronian 4late EoceneA leptomerycid†L. mammiferChadronian 3late EoceneA leptomerycid. The main index taxon of the Chadronian 3.†L. yoderiChadronian 2late EoceneA leptomerycid. The main index taxon of the Chadronian 2.†Parvitragulus†P. priscusChadronianlate EoceneA very small praetragulid†Santuccimeryx†S. elissaeOrellan 3 - Whitneyan 1early - "mid" OligoceneA tiny brachycephalic leptomerycid, formerly considered a species of Leptomeryx but seemingly transitional to later leptomerycids.Shreero, Mattison; Welsh, Ed; Marriott, Katherine; Prothero, Donald R. (2023). "A tiny deer with big implications: a new genus (Santuccimeryx) from Badlands National Park helps bridge the gap between Oligocene and Miocene Leptomerycidae (Mammalia, Artiodactyla)". Proceedings of the South Dakota Academy of Science. 102: 59–81.
Suina A few suines (pig-like mammals) are rare components of the White River fauna. These species are sometimes regarded as the earliest peccaries (family Tayassuidae), though other times considered early suines which split off prior to the common ancestor between peccaries and Old World pigs (family Suidae). GenusSpeciesNALMAEpochNotesImage†Perchoerus†P. minorChadronian 2 - 4late EoceneA very small early peccary or a close relative†P. nanusOrellanearly OligoceneA small early peccary or a close relative†P. probusWhitneyan"mid" OligoceneA medium-sized early peccary or a close relative
Carnivorans
†Amphicyonids