Subhyracodon
Fossil rangeLate Eocene to Late Oligocene, [1]
TaxonSubhyracodon
AuthorityBrandt, 1878
Type speciesSubhyracodon occidentalis
Subdivision ranksSpecies
Subdivision
  • †S. kewi
  • †S. mitis
  • †S. occidentalis
Synonyms

Subhyracodon (Latin: "below the genus Hyracodon"[4]) is an extinct genus of hornless rhinocerotids.

Description

With a length of 2.4 m (7.9 ft) and an estimated weight of 381 kg (840 lb) in S. mitis,[citation needed] it was a tapir-sized herbivore on the plains of early Oligocene South Dakota 33 million years ago. It coexisted with other perissodactyls such as horses, brontotheres, and chalicotheres.[5] Subhyracodon had no horns, relying more on its speed to escape from predators, but a species found at Wind Cave National Park had a pair of bony nasal ridges.[citation needed] The genus Caenopus and species originally referred to as Aceratherium were synonymized into Subhyracodon.[6] It has been suggested to be one of the oldest known members of the subfamily Elasmotheriinae by some studies,[7] though other studies place it firmly outside the Rhinocerotinae-Elasmotheriinae split,[8] with a 2025 study placing it as one of the most basal rhinoceroses.[9] In terms of dentition, Subhyracodon was similar to other White River rhinoceroses, bearing no canines or third incisors. The incisor formula of Subhyracodon is .[10]

Classification

Cladogram after Borrani et al. 2025:[9]

References

  1. ^ Prothero, 2005, p. 41.
  2. ^ McKenna & Bell, 1997, p. 481.
  3. ^ Prothero, 2005, p. 43.
  4. ^ "Glossary. American Museum of Natural History". Archived 20 November 2021 at the Wayback Machine.
  5. ^ "Paleobiology Database: Subhyracodon mitis". Archived from the original on 2012-07-10. Retrieved 2012-05-29.
  6. ^ C.C. O'Harra (1920). The White River Badlands. Rapid City, SD: South Dakota School of Mines. p. 181.
  7. ^ Kosintsev, Pavel; Mitchell, Kieren J.; Devièse, Thibaut; van der Plicht, Johannes; Kuitems, Margot; Petrova, Ekaterina; Tikhonov, Alexei; Higham, Thomas; Comeskey, Daniel; Turney, Chris; Cooper, Alan; van Kolfschoten, Thijs; Stuart, Anthony J.; Lister, Adrian M. (2018-11-26). "Evolution and extinction of the giant rhinoceros Elasmotherium sibiricum sheds light on late Quaternary megafaunal extinctions". Nature Ecology & Evolution. 3 (1): 31–38. Bibcode:2018NatEE...3...31K. doi:10.1038/s41559-018-0722-0. hdl:1887/82017. ISSN 2397-334X. PMID 30478308. S2CID 53726338
  8. ^ Geraads, Denis & Zouhri, Samir (2021). "A new late Miocene elasmotheriine rhinoceros from Morocco". Acta Palaeontologica Polonica. 66. doi:10.4202/app.00904.2021
  9. ^ Borrani, Antonio; Mackiewicz, Paweł; Kovalchuk, Oleksandr; Barkaszi, Zoltán; Capalbo, Chiara; Dubikovska, Anastasiia; Ratajczak‐Skrzatek, Urszula; Sinitsa, Maxim; Stefaniak, Krzysztof; Mazza, Paul P.A. (2025-10-26). "The evolutionary history of Rhinocerotidae: phylogenetic insights, climate influences and conservation implications". Cladistics. doi:10.1111/cla.70015. hdl:2158/1444059. ISSN 0748-3007
  10. ^ Scott, William Berryman (1913). A history of land mammals in the western hemisphere. New York, The MacMillan Company.