Hippidion Explained

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,[1] this was later shown to be incorrect, with more complete sequences finding Hippidion as an outgroup to all living equines[2] and less closely related to living equines than the North American "New World stilt legged horse", Haringtonhippus francisci. Cladogram shown below:[3]

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.[4] [5] 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[6] 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.[7]

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 NaNkg (-2,147,483,648lb), while specimens of H. devillei have been estimated to weigh in the region of NaNkg (-2,147,483,648lb). H. principale was somewhat larger, with an estimated mass range of NaNkg (-2,147,483,648lb).[8] 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.[9]

Paleobiology

Isotopic evidence from δ13C suggests that Hippidion consumed plants of either C3 or mixed C3 and C4 type carbon fixation.[10] The δ13C 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.[11]

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.[12] 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.[13] [14]

Notes and References

  1. Weinstock . J. . Willerslev . Eske . Sher . Andrei . Tong . Wenfei . Ho . Simon Y.W. . Rubenstein . Dan . Storer . John . Burns . James . Martin . Larry . 1 . 2005 . Evolution, systematics, and phylogeography of Pleistocene horses in the New World: a molecular perspective . . 3 . 8 . e241 . 10.1371/journal.pbio.0030241 . 1159165 . 15974804 . free.
  2. Der Sarkissian . Clio . Vilstrup . Julia T. . Schubert . Mikkel . Seguin-Orlando . Andaine . Eme . David . Weinstock . Jacobo . Alberdi . Maria Teresa . Martin . Fabiana . Lopez . Patricio M. . Prado . Jose L. . Prieto . Alfredo . March 2015 . Mitochondrial genomes reveal the extinct Hippidion as an outgroup to all living equids . Biology Letters . en . 11 . 3 . 20141058 . 10.1098/rsbl.2014.1058 . 1744-9561 . 4387498 . 25762573.
  3. Heintzman . P.D. . Zazula . G.D. . MacPhee . R.D.E . Scott . E. . Cahill . J.A. . McHorse . B.K. . Kapp . J.D. . Stiller . M. . Wooller . M.J. . Orlando . L. . Southon . J. . Froese . D.G. . Shapiro . B. . 2017 . A new genus of horse from Pleistocene North America . eLife . 6 . 10.7554/eLife.29944 . 5705217 . 29182148 . free.
  4. Santos Avilla . Leonardo Dos . Bernardes . Camila . Mothé . Dimila . 2015-05-04 . A new genus for Onohippidium galushai Macfadden and Skinner, 1979 (Mammalia, Equidae), from the late Hemphillian of North America . Journal of Vertebrate Paleontology . en . 35 . 3 . e925909 . 10.1080/02724634.2014.925909 . 2015JVPal..35E5909S . 0272-4634.
  5. 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.
  6. Orlando . L. . 2008 . Ancient DNA Clarifies the Evolutionary History of American Late Pleistocene Equids . . 66 . 5. 533–538 . 10.1007/s00239-008-9100-x . 18398561 . 1 . Male . Dean . Alberdi . Maria Teresa . Prado . Jose Luis . Prieto . Alfredo . Cooper . Alan . Hänni . Catherine . 2008JMolE..66..533O . 19069554 .
  7. Prado . José . Alberdi . María . 2023 . Diversity of the fossil equidsfrom South America . Publicación Electrónica de la Asociación Paleontológica Argentina . 23 . 1 . 241–254 . 10.5710/PEAPA.06.06.2022.415. free .
  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 . en . 40 . 6 . e1862132 . 10.1080/02724634.2020.1862132 . 2020JVPal..40E2132L . 233706381 . 0272-4634.
  9. 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 . 10.4202/app.2011.0107. free .
  10. 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 . en . 11 . 1 . 15 . 10.1186/1472-6785-11-15 . free . 1472-6785 . 3129290 . 21672241. 2011BMCE...11...15P .
  11. 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 . en . 225 . 106025 . 10.1016/j.quascirev.2019.106025. 2019QSRv..22506025M . 210240458 .
  12. Villavicencio. Natalia A.. Corcoran. Derek. Marquet. Pablo A.. 2019-06-27. Assessing the Causes Behind the Late Quaternary Extinction of Horses in South America Using Species Distribution Models. Frontiers in Ecology and Evolution. 7. 226. 10.3389/fevo.2019.00226. 2296-701X. free.
  13. Bampi . Hugo . Barberi . Maira . Lima-Ribeiro . Matheus S. . December 2022 . Megafauna kill sites in South America: A critical review . Quaternary Science Reviews . en . 298 . 107851 . 2022QSRv..29807851B . 10.1016/j.quascirev.2022.107851 . 253876769.
  14. Nami . Hugo G. . 2019-08-12 . Paleoamerican Occupation, Stone Tools from the Cueva del Medio, and Considerations for the Late Pleistocene Archaeology in Southern South America . Quaternary . en . 2 . 3 . 28 . 10.3390/quat2030028 . 2571-550X . free . free . 11336/120270.

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