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Hippidion Temporal range: Late Pliocene-Holocene (Uquian-Lujanian) ~2.5–0.011 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
H. principale skeleton
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Family:	Equidae
Subfamily:	Equinae
Tribe:	Equini
Genus:	†Hippidion Owen, 1869
Species
H. principale (Lund, 1846) (type) H. saldiasi Roth, 1899 H. devillei (Gervais, 1855)
Synonyms
Hipphaplous Ameghino 1882 Hipphaplus Ameghino 1882 Onohippidion Filhol 1888 Onohippidium Moreno 1891 Parahipparion Ameghino 1904

Hippidion (meaning little horse) is an extinct genus of equine that lived in South America from the Late Pliocene to the end of the Late Pleistocene (Lujanian), between 2.5 million and 11,000 years ago. They were one of two lineages of equines native to South America during the Pleistocene epoch, alongside Equus (Amerhippus) neogeus.

Taxonomy

Evolution

Although early ancient DNA analysis studies suggested a close relationship with the wild horse, Equus ferus, this was later shown to be incorrect, with more complete sequences finding Hippidion as an outgroup to all living equines and less closely related to living equines than the North American "New World stilt legged horse", Haringtonhippus francisci. Cladogram shown below:

Hippidion is part of a distinct lineage of equines belonging to the tribe Equini that are suggested to have diverged from the ancestors of living equines of the genus Equus at least 6 million years ago. The earliest members of the Hippidion lineage are known from the Late Miocene of North America. Hippidion migrated into the South American continent at the Pliocene-Pleistocene transition, around 2.5 million years ago as part of the Great American Biotic Interchange with the hippidiform lineage becoming extinct in North America during the Early Pleistocene. It is disputed as to whether Hippidion is an exclusively South American genus or whether remains from North America are attributable to it.

Hippidion is traditionally thought to have 3 species, H. principale, H. saldiasi and H. devillei, however, in a 2015 DNA analysis, the single sampled H. principale specimen was found to be nested with H. saldiasi, while H. devillei was found to be clearly genetically distinct.

Description

Specimens of Hippidion saldiasi have been estimated to weigh in the range of 252.7–326.4 kilograms (557–720 lb), while specimens of H. devillei have been estimated to weigh in the region of 227.3–366.5 kilograms (501–808 lb). H. principale was somewhat larger, with an estimated mass range of 252.7–468.6 kilograms (557–1,033 lb). The skull of Hippidion is noted for its very long nasal notch separating the elongate nasal bone from the rest of the skull. This structure is suggested to correspond to the presence of a prehensile upper lip. The teeth morphology is more similar to that of Pliohippus than to Equus. The limb bones are short and stocky (robust).

Paleobiology

Isotopic evidence from δC suggests that Hippidion consumed plants of either C₃ or mixed C₃ and C₄ type carbon fixation. The δC values are consistent with the occupation of woodland and wooded grassland habitats. H. principale is suggested to have been a mixed feeder (both browsing and grazing), as opposed to the grazing diet of the contemporary Equus neogeus. Hippidion has been suggested to have probably lived in herds like living equines.

Distribution

Fossils of Hippidion have been found across South America. Hippidion principale is primarily known from the Pampas grasslands of Argentina, but its range may have extended to Peru and Ecuador. Hippidion devillei is also known from Argentinan Pampas, but is also found in the Peruvian central Andes, with remains possibly found in Venezuela. Hippidion saldiasi was native to the Southern Cone, including Patagonia and the southern Andes.

Extinction

Hippidion became extinct alongside the other South American equines at the end of the Late Pleistocene, between 12,000 and 10,000 years Before Present (BP) as part of the Late Pleistocene megafauna extinctions, which resulted in the extinction of most large animals in both North and South America. Climatic modelling suggests that the preferred habitat for species of Hippidion declined after the Holocene transition, but the decline is not enough to explain the extinction. At the Arroyo Seco 2 site in the Argentinan Pampas (14,782–11,142 cal yr BP), and Piedra Museo site in Santa Cruz Province, Patagonia (two separate layers dating to 12,463–10,457 cal yr BP and 15,517–12,352 cal yr BP), as well as the similarly aged Cueva del Medio site in southern Chile remains of Hippidion are associated with human artifacts, including Fishtail projectile points, and bear cut marks, indicating that they were hunted by recently arrived humans, which may have played a role in their extinction.

References

1. ^ Weinstock, J.; et al. (2005). "Evolution, systematics, and phylogeography of Pleistocene horses in the New World: a molecular perspective". PLOS Biology. 3 (8): e241. doi:10.1371/journal.pbio.0030241. PMC 1159165. PMID 15974804.
2. ^ Orlando, L.; et al. (2008). "Ancient DNA Clarifies the Evolutionary History of American Late Pleistocene Equids". Journal of Molecular Evolution. 66 (5): 533–538. Bibcode:2008JMolE..66..533O. doi:10.1007/s00239-008-9100-x. PMID 18398561. S2CID 19069554.
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6. ^ MacFadden, B. J., and M. Skinner. 1979. Diversification and biogeography of the one-toed horses Onohippidium and Hippidion. Yale Peabody Museum of Natural History Postilla 175:1–9.
7. Prado, José; Alberdi, María (2023). "Diversity of the fossil equidsfrom South America". Publicación Electrónica de la Asociación Paleontológica Argentina. 23 (1): 241–254. doi:10.5710/PEAPA.06.06.2022.415.
8. ^ Labarca, Rafael; Caro, Francisco J.; Villavicencio, Natalia A.; Capriles, José M.; Briones, Esteban; Latorre, Claudio; Santoro, Calogero M. (2020-12-10). "A partially complete skeleton of Hippidion saldiasi Roth, 1899 (Mammalia: Perissodactyla) from the late Pleistocene of the high Andes in northern Chile". Journal of Vertebrate Paleontology. 40 (6): e1862132. Bibcode:2020JVPal..40E2132L. doi:10.1080/02724634.2020.1862132. ISSN 0272-4634. S2CID 233706381.
9. Prado, José Luis; Alberdi, María Teresa (2017), "Nomenclatures and Taxonomy", Fossil Horses of South America, Cham: Springer International Publishing, pp. 7–59, doi:10.1007/978-3-319-55877-6_2, ISBN 978-3-319-55876-9, retrieved 2024-01-19
10. Bernardes, Camila; Sicuro, Fernando L.; Avilla, Leonardo S.; Pinheiro, André E.P. (2012). "Rostral reconstruction of South American hippidiforms (Mammalia, Perissodactyla, Equidae): New anatomical and ecomorphological inferences". Acta Palaeontologica Polonica. doi:10.4202/app.2011.0107.
11. Cirilli, Omar; Machado, Helena; Arroyo-Cabrales, Joaquin; Barrón-Ortiz, Christina I.; Davis, Edward; Jass, Christopher N.; Jukar, Advait M.; Landry, Zoe; Marín-Leyva, Alejandro H.; Pandolfi, Luca; Pushkina, Diana; Rook, Lorenzo; Saarinen, Juha; Scott, Eric; Semprebon, Gina (September 2022). "Evolution of the Family Equidae, Subfamily Equinae, in North, Central and South America, Eurasia and Africa during the Plio-Pleistocene". Biology. 11 (9): 1258. doi:10.3390/biology11091258. hdl:2158/1282959. ISSN 2079-7737. PMID 36138737.
12. Prado, José L; Sánchez, Begoña; Alberdi, María T (December 2011). "Ancient feeding ecology inferred from stable isotopic evidence from fossil horses in South America over the past 3 Ma". BMC Ecology. 11 (1): 15. Bibcode:2011BMCE...11...15P. doi:10.1186/1472-6785-11-15. ISSN 1472-6785. PMC 3129290. PMID 21672241.
13. Prado, José Luis; Alberdi, María Teresa (2017), "Ancient Feeding Ecology and Niche Differentiation of Pleistocene Horses", Fossil Horses of South America, Cham: Springer International Publishing, pp. 101–118, doi:10.1007/978-3-319-55877-6_6, ISBN 978-3-319-55876-9, retrieved 2024-01-20
14. Morosi, Elizabeth; Ubilla, Martin (December 2019). "Feeding and environmental studies on late Pleistocene horses in mid-latitudes of South America (northern Uruguay)". Quaternary Science Reviews. 225: 106025. Bibcode:2019QSRv..22506025M. doi:10.1016/j.quascirev.2019.106025. S2CID 210240458.
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v t e Perissodactyla
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Perissodactyla
Perissodactyla Incertae sedis †Ghazijhippus †Mesolambdolophus †Olbitherium †Anthracobunia Radinskya †Anthracobunidae Anthracobune Hsanotherium Jozaria Obergfellia †Cambaytheriidae Cambaytherium Kalitherium Nakusia Perissobune †Brontotheriidae See Brontotheriidae Equoidea †Cymbalophus †Hallensia †Pliolophus †Systemodon Equidae See Equidae †Palaeotheriidae †Pachynolophinae Anchilophus Bepitherium Eurohippus Hyracotherium Lijiangia Lophiohippus Lophiotherium Metanchilophus Orolophus Pachynolophus Paranchilophus Propalaeotherium Qianohippus †Palaeotheriinae Cantabrotherium Iberolophus Idiodontherium Leptolophus Mekodontherium Metaplagiolophus Palaeotherium Paraplagiolophus Plagiolophus Pseudopalaeotherium †Hyopsodontidae? Aletodon Chacomylus Dorraletes Haplaletes Haplomylus Hyopsodus Litomylus Louisina Monshyus Paratricuspiodon Paschatherium Phenacodaptes Tricuspiodon †Phenacodontidae? Tetraclaenodon †Meniscotheriinae Ectocion Meniscotherium †Phenacodontinae Almogaver Copecion Eodesmatodon Lophocion Phenacodus Tapiromorpha See below↓
Tapiromorpha Incertae sedis †Cambaylophus †Skopaiolophus †Isectolophidae Chowliia Gandheralophus Karagalax Meridiolophus Orientolophus Sastrilophus †Homogalaxinae Homogalax †Isectolophinae Isectolophus Schizolophodon †Ancylopoda See Ancylopoda Ceratomorpha Tapiroidea †Deperetellidae Bahinolophus Deperetella Irenolophus Teleolophus †Helaletidae Colodon Dilophodon Helaletes Heptodon Heteraletes Paracolodon Plesiocolopirus Thuliadanta? Vastanolophus Tapiridae †Eotapirus †Miotapirus †Nexuotapirus †Paratapirus †Plesiotapirus †Protapirus †Tapiravus Tapirus Rhinocerotoidea See below↓
Rhinocerotoidea Rhinocerotoidea sensu lato †Breviodon †Fouchia †Minchenoletes †Siamolophus †Triplopus †Yimengia †Indolophidae Indolophus Rhinocerotoidea sensu stricto †Selenaletes †Hyrachyidae Hyrachyus †Eggysodontidae Allacerops Eggysodon Guangnanodon Proeggysodon †Hyracodontidae Ardynia Ephyrachyus Epitriplophus Hyracodon Prohyracodon Rhodopagus Triplopides †Amynodontidae Amynodontopsis Armania Cadurcotherium Caenolophus Huananodon Hypsamynodon Procadurcodon Rostriamynodon Teilhardia †Amynodontinae Amynodon †Cadurcodontini Cadurcodon Lushiamynodon Sharamynodon Sianodon †Metamynodontini Gigantamynodon Megalamynodon Metamynodon Paramynodon Zaisanamynodon †Paraceratheriidae †Forstercooperiinae Forstercooperia Gobicerops Pappaceras †Paraceratheriinae Aralotherium Dzungarotherium Juxia Paraceratherium Urtinotherium Rhinocerotidae See below↓
Rhinocerotidae Rhinocerotidae †Amphicaenopus †Epiaceratherium †Guixia †Teletaceras †Uintaceras †Woodoceras †Aceratheriinae Aceratherium Acerorhinus Alicornops Aphelops Chilotheridium Chilotherium Floridaceras Galushaceras Hoploaceratherium Mesaceratherium Peraceras Persiatherium Plesiaceratherium Ronzotherium Shansirhinus Sinorhinus Subchilotherium †Elasmotheriinae Gulfoceras Victoriaceros †Diceratheriini Diceratherium Penetrigonias Skinneroceras Subhyracodon Trigonias †Elasmotheriini Bugtirhinus Caementodon Elasmotherium Hispanotherium Iranotherium Kenyatherium Meninatherium Menoceras Ninxiatherium Ningxiatherium Ougandatherium Parelasmotherium Procoelodonta Sinotherium Tongxinotherium Rhinocerotinae †Dromoceratherium †Lartetotherium †Molassitherium †Protaceratherium †Teleoceratini Aprotodon Brachydiceratherium Brachypotherium Diaceratherium Prosantorhinus Shennongtherium Teleoceras Rhinocerotina Dicerorhinini †Coelodonta Dicerorhinus †Dihoplus †Pliorhinus †Stephanorhinus Dicerotini Ceratotherium Diceros †Miodiceros †Paradiceros Rhinocerotini †Gaindatherium †Nesorhinus Rhinoceros †Rusingaceros

• Pliocene horses
• Pleistocene horses
• Pliocene first appearances
• Pleistocene genus extinctions
• Prehistoric placental genera
• Pleistocene mammals of South America
• Pliocene mammals of South America
• Uquian
• Ensenadan
• Lujanian
• Pleistocene Argentina
• Fossils of Argentina
• Pleistocene Bolivia
• Fossils of Bolivia
• Pleistocene Brazil
• Fossils of Brazil
• Pleistocene Chile
• Fossils of Chile
• Sopas Formation
• Dolores Formation, Uruguay
• Fossils of Uruguay
• Pleistocene Venezuela
• Fossils of Venezuela
• Fossil taxa described in 1869
• Equini