In Depth
Hipparion was one of the earlier grazing horses that was similar to Merychippus in form. Like other ‘advanced’ horses of the Miocene, Hipparion supported its body weight upon a single toe that ended with a hoof. Other toes were also still present upon either side of this toe, but they had become so reduced in size that they did not even touch the ground. In later forms like Pliohippus the toes would be virtually absent.
The key to fame for Hipparion is the amazing success that this genus exhibited. Although perhaps nothing special in terms of appearance, Hipparion appeared at the start of the Miocene period and continued to thrive until well into the mid Pleistocene, surviving for some twenty-two million years. In the space of this time Hipparion colonised most of the major continents with the exception of Antarctica, Australia and South America. The former two were separated by sea preventing land animals from colonising these continents. South America was not joined to North America until the creation of the Isthmus of Panama in the late Pliocene, and since North American remains of Hipparion are dated to the end of the Miocene at latest, it’s probable that Hipparion was not around in this continent at a time to take part in the Great American Interchange which saw a mixing of previously isolated animals, thus missing the chance to colonise South America as well.
Hipparion would have been a horse of open plains and steppe, a far cry from its browsing ancestors that would have lurked amongst the bushes hiding from predators. The key adaption that Hipparion had for these habitats were high crowned teeth that were better suited for processing grasses which would have formed the most abundant type of plant that also readily replenished itself.
Despite its success after the Miocene, Hipparion was living in a world that saw the emergence of more advanced horses, all the way up to the point where the modern forms began to appear. These new forms as well as other new grazing animals such as mammoths would have meant increased competition for the same resources that Hipparion used. There is of course the consideration of the emergence of new predators such as cave hyena which seems to have actively hunted horse by the greater numbers of horse remains compared to other animals found in association with them. All of these new animals appearing would have gradually edged Hipparion into extinction long before the near total disappearance of the megafauna at the end of the Pleistocene.
Further Reading
– Lower Pliocene horses from Black Hawk Ranch, Mount Diablo, California. – University of California Publications, Bulletin of the Department of Geological Sciences 28(1):1-44. – K. A. Richey – 1948. – [Pliocene vertebrates of Lantain, Shensi]. – Professional Papers of Stratigraphy and Palaeontology 7:149-200. – T.-S. Liu, C.-K. Li & R.-J. Zhai – 1978. – The Miocene Horse Hipparion From North America and From Type Locality in Southern France – Palaeontology, vol23 part 3 pp. 617-635. – Bruce J. MacFadden – 1980. – Systematics and phylogeny of Hipparion, Neohipparion, Nannippus, and Cormohipparion (Mammalia, Equidae) from the Miocene and Pliocene of the New World. – Bulletin of the American Museum of Natural History 179(1):1-195. – B. J. MacFadden – 1984. – New species of Hipparion from La Roma 2 (Late Vallesian; Teruel Spain): a study of the morphological and biometric variability of Hipparion primigenium. – Journal of Paleontology 80(2):343-356. – M. D. Pesquero, M. T. Alberdi & L. Alcal� – 2006.
