Odd-toed Ungulate - Taxonomy

Taxonomy

The members of the order fall into two suborders:

• Hippomorpha are odd-toed ungulates that are, today, fast runners with long legs and have only one toe. The only extant family of this suborder is Equidae (whose sole surviving genus is Equus), comprising the horse, zebra, donkey, onager, and allied species. The extinct, rhinoceros-like brontotheres are also included in this suborder. Both families probably descended from palaeotheres.
• Ceratomorpha have several functional toes; they are heavier than and move more slowly than the Hippomorpha. This suborder has two extant families: Tapiridae (tapirs) and Rhinocerotidae (rhinoceroses). The extinct chalicotheres may belong to this suborder as well.

The three surviving families of odd-toed ungulate are classified as follows:

• ORDER PERISSODACTYLA
  • Suborder Hippomorpha
    • Family Equidae: horses and allies, seven species in one genus
      • Wild horse, Equus ferus
        • Przewalski's horse, Equus ferus przewalskii
        • Domestic horse, Equus ferus caballus
      • African wild ass Equus africanus
        • Domesticated ass (donkey) Equus africanus asinus
      • Onager or Asiatic ass, Equus hemionus
      • Kiang or Tibetan wild ass, Equus kiang
      • Plains zebra, Equus quagga
      • Mountain zebra, Equus zebra
        • Cape mountain zebra, Equus zebra zebra
        • Hartmann's mountain zebra, Equus zebra hartmannae
      • Grevy's zebra, Equus grevyi
  • Suborder Ceratomorpha
    • Family Tapiridae: tapirs, four species in one genus
      • Brazilian tapir, Tapirus terrestris
      • Mountain tapir, Tapirus pinchaque
      • Baird's tapir, Tapirus bairdii
      • Malayan tapir, Tapirus indicus
    • Family Rhinocerotidae: rhinoceroses, five species in four genera
      • Black rhinoceros, Diceros bicornis
      • White rhinoceros, Ceratotherium simum
      • Indian rhinoceros, Rhinoceros unicornis
      • Javan rhinoceros, Rhinoceros sondaicus
      • Sumatran rhinoceros, Dicerorhinus sumatrensis

Based on morphology, odd-toed ungulates were long thought to form a clade with even-toed ungulates. However, recent phylogenetic studies have lacked full confidence in this conclusion; some studies link Perissodactyla with Ferae into a proposed clade Zooamata, while the Pegasoferae proposal goes further, suggesting Chiroptera (bats) are more closely related to odd-toed ungulates than even-toed ones. The most recent study, by Zhou et al. (2011), finds better (but not full) support for the traditional view, uniting Perissodactyla with Cetartiodactyla into a clade of "true ungulates", Euungulata.