Pliohippus
| Pliohippus | ||||||||||||
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Skull, skeleton and foot of Pliohippus |
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| Temporal occurrence | ||||||||||||
| Middle Miocene ( Barstovian ) to Lower Pliocene ( Hemphilian ) | ||||||||||||
| 16 to 4.9 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Pliohippus | ||||||||||||
| Marsh , 1874 | ||||||||||||
Pliohippus is an extinct genus from the Equidae family thatlived on the North American continent and in Central America from the Middle Miocene to the Lower Pliocene 16 to around 5 million years ago.
features
Pliohippus was a relative of today's horses of the genus Equus and already resembled them quite clearly, but was a bit smaller and probably reached a maximum of the dimensions of the smallest Equus species known today , the weight was around 170 kg. A clear connection to the recent representatives is the presence of only a single toe per limb, which was also quite wide, which can be interpreted as an adaptation to life in the open grass landscape and for rapid movement on the hard steppe underground . However, there were still two small reduced toes ( stylus legs ) on the side. A striking difference is the presence of a facial fossa (pre-orbital fossa). Such pit formation is typical of Neogene horses , but was lost again in Equus . It was located just in front of the orbit and reached a diameter of around 15 mm, with it being surrounded almost all around by bones. The dentition consisted of the complete dentition of modern mammals , in contrast to most of today's horses, Pliohippus still had a functional first premolar . The rear teeth in particular consisted of high-crowned ( hypsdontal ) molars with strongly curved enamel folds , which were ideally suited to chewing the hard grass. However, the enamel fold patterns differed somewhat from those of today's horses and were designed more primitively. The molars reached crown heights of 5 to 6.5 cm, the entire chewing row was 14 to 18 cm long.
Fossil finds
Pliohippus was distributed over large parts of North America during the Middle Miocene to the Lower Pliocene around 16 to 5 million years ago and has been a very dominant herbivore. It is proven from California in the west over the Great Plains in the north to the coast on the Gulf of Mexico in the east and south in Mexico . Significant finds come from the Mint Canyon Formation of the Upper Miocene, where, among other things, an almost complete skull was discovered. A partial skeleton from the area of the Niobrara River in Nebraska served as the holotype for the first description . Partly complete skeletons are from the Ash Hollow Formation , which is also common in Nebraska. The animals died in the beginning of the Upper Miocene from a massive volcanic eruption . Finds from Oaxaca in Mexico are very far to the south and include several molars and also represent the oldest known material in terms of phylogenetic history.
Paleobiology
Not only the high-crowned teeth of Pliohippus indicate a specialization in hard grass food , this could also be determined by means of isotope tests. The finds from Oaxaca, located very far south of Mexico, suggest that the horse species was not only adapted to dry and cool steppe conditions, but could also cope with warmer climates. In large areas of its distribution in what is now the southern part of the USA , however, it lived in open bush and grasslands, with an annual rainfall of 1220 to 1360 mm, especially in the late Miocene, is assumed.
Systematics
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Internal systematics of the Equidae according to Prado and Alberdi 1996 and Mihlbachler et al. 2011
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Pliohippus is an extinct genus from the family of the Equidae (horses) and is placed within this in the more modern subfamily of the Equinae , which is characterized by better adaptation to grass food and thus developed hypsodontic teeth. Here again it belongs to the tribe of the Equini and the sub- tribus of the Pliohippina , where it is placed at their base. Thus Pliohippus is the sister taxon to all other modern horses. The Pliohippina comprise the single-hoofed horses, a feature that all modern representatives of the genus Equus have. They in turn represent the sister group of the Protohippina , which are designed a bit more primitive. The Equini, for their part, are opposed to the Hipparionini (in some systematics the Protohippina are also led on the tribe level (Protohippini) within the Equinae and then form the sister group to the Hipparionini). The closest relative to Pliohippus is Astrohippus , which was originally listed as a subgenus of Pliohippus .
The name was introduced in 1874 by Othniel Charles Marsh using a partial skeleton from Nebraska together with the type species P. pernix . Later in 1918 Henry Fairfield Osborn distinguished a total of 16 different species, some of which are now assigned to Equus , others to Astrohippus and Dinohippus . A total of 5 species from the genus Pliohippus are currently recognized:
- P. fossulanus Cope , 1893
- P. mirabilis ( Leidy , 1858)
- P. nobilis Osborn , 1918
- P. pernix Marsh , 1874
- P. tantalus Merriam , 1913
Individual evidence
- ↑ a b Mark T. Clementz, Patricia A. Holroyd, Paul L. Koch: Identifying Aquatic Habits Of Herbivorous Mammals Through Stable Isotope Analysis. In: Palaios. 23 (9), 2008, pp. 574-585.
- ^ Thomas S. Kelly: New Miocene horses from the Caliente Formation, Cuyama Valley Badlands, California. In: Contribution in Sciences. 455, 1995, pp. 1-44.
- ↑ a b Thomas S. Kelly: New Middle Miocene equid crania from and their implications for the phylogeny of the Equini. In: Contribution in Sciences. 455, 1998, pp. 1-33.
- ^ A b c d Victor M. Bravo-Cuevas, Ismael Ferrusquía-Villafranca: The oldest record of Equini (Mammalia: Equidae) from Mexico. In: Revista Mexicana de Ciencias Geológicas. 27, 2010, pp. 593-602.
- ↑ Bruce J. MacFadden: Fossil Horses. Systematic, Paleobiology, and Evolution of the family Equidae. Cambridge University Press, 1992, pp. 71-72.
- ↑ Danielle Fraser, Jessica M. Theodor: Ungulate diets reveal patterns of grassland evolution in North America. In: Palaeogeography, Palaeoclimatology, Palaeoecology. 369, 2013, pp. 409-421.
- ^ A b José L. Prado, María T. Alberdi: A cladistic analysis of the horses of the tribe Equini. In: Journal of Palaeontology. 39 (3), 1996, pp. 663-680.
- ^ A b Matthew C. Mihlbachler, Florent Rivals, Nikos Solounias, Gina M. Semperbon: Dietary Change and Evolution of Horses in North America. In: Science. 331, 2011, pp. 1178-1181.
- ^ José Luis Prado, María Teresa Alberdi: Fossil Horses of South America. Phylogeny, Systemics and Ecology. Springer International Publishing, 2017, pp. 73–84.
- ^ Christine M. Janis, Raymond I. Bernor: The Evolution of Equid Monodactyly: A Review Including a New Hypothesis. In: Frontiers in Ecology and Evolution. 7, 2019, p. 119, doi: 10.3389 / fevo.2019.00119 .
- ↑ Bruce J. MacFadden: Astrohippus and Dinohippus from the Yepomera Local Fauna (Hemphillian, Mexico) and Implications for the Phylogeny of One-Toed Horses. In: Journal of Vertebrate Paleontology. 4 (2), 1984, pp. 273-283.
