Perissodactyla (Odd‐Toed Ungulates Including Horses, Rhinoceroses and Tapirs)


The mammalian order Perissodactyla, or ‘odd‐toed’ ungulates, includes the living horses, rhinoceroses and tapirs, and two extinct groups, the brontotheres and chalicotheres. Over their 55 million years, they evolved into an amazing variety of forms, and about 40 million years ago, they were the dominant hoofed mammals on the planet. Since then, they have been largely replaced by the even‐toed artiodactyls, and today most wild perissodactyl species are on the brink of extinction.

Keywords: horse; rhinoceros; tapir; mammals; hyrax

Figure 1.

Specializations that define the perissodactyls. (a) Left hind feet of typical perissodactyls, with a line drawn through the axis of symmetry in the third toe. They include (from left) the tapir Tapirus, the primitive three‐toed horse Protorohippus, the modern one‐toed horse Equus, the brontothere Brontops, and the clawed chalicothere Moropus. Between these last two feet is the ankle bone, or astragalus, of a typical perissodactyl, with its flat, saddle‐shaped lower facet. (Modified from Colbert and Morales, 1991.) (b) Crown view of right upper first, second and third molars of typical perissodactyls, showing the characteristic connection of cusps by crests in different groups. The cheek is towards the top, the tongue towards the bottom, and the front of the mouth towards the right in each example. Top row, left: the primitive horse Protorohippus, with four distinct cusps and only weak crests connecting them. Top row, right: the primitive tapir Homogalax, with strong cross‐crests connecting the cusps. Second row, left: the rhinoceros Subhyracodon, with crests connected so that they resemble the Greek letter π (‘pi’). Second row, right: the brontothere Palaeosyops, with the typical ‘W’‐shaped outer crest, and large blunt inner cusps. Bottom row: the chalicothere Moropus, with the ‘W’‐shaped outer crest partially connected to the inner cusps with crests. (Modified from Romer, 1966.)

Figure 2.

Family tree of the perissodactyls.


Further Reading

Colbert EH and Morales M (1991) Evolution of the Vertebrates, 5th edn. New York: John Wiley.

Fischer MS and Tassy P (1993) The interrelation between Proboscidea, Sirenia, Hyracoidea, and Mesaxonia: the morphological evidence. In: Szalay FS, Novacek MJ and McKenna MC (eds) Mammal Phylogeny: Placentals, pp. 217–234. New York: Springer‐Verlag.

Janis CM (1976) The evolutionary strategy of the Equidae, and the origins of rumen and cecal digestion. Evolution 30: 757–774.

Janis CM, Colbert MW, Coombs MC et al. (1998) Perissodactyla and Proboscidea. In: Janis CM, Scott KM and Jacobs LL (eds) Evolution of Tertiary Mammals of North America, vol. I: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals, pp. 511–524. Cambridge: Cambridge University Press.

MacDonald D (1984) All the Worlds Animals: Hoofed Mammals. New York: Torstar Books.

MacFadden BJ (1994) Fossil Horses. New York: Cambridge University Press.

Owen‐Smith N (1988) Megaherbivores. Cambridge: Cambridge University Press.

Prothero DR (1987) The rise and fall of the American rhino. Natural History 96: 26–33.

Prothero DR and Schoch RM (eds) (1989) The Evolution of Perissodactyls. New York: Oxford University Press.

Prothero DR and Schoch RM (2000) The Evolution of Hoofed Mammals and their Relatives. Baltimore: Johns Hopkins University Press.

Prothero DR, Manning E and Fischer MS (1988) The phylogeny of the ungulates. In: Benton MJ (ed.) The Phylogeny and Classification of the Tetrapods, vol. II: Mammals, pp. 201–234. Oxford: Oxford University Press.

Romer AS (1966) Vertebrate Paleontology. Chicago: University of Chicago Press.

Savage RJG, and Long MR (1986) Mammal Evolution: An Illustrated Guide. New York: Facts‐on‐File Publications.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Prothero, Donald R(Apr 2001) Perissodactyla (Odd‐Toed Ungulates Including Horses, Rhinoceroses and Tapirs). In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001569]