Science Fair Project Encyclopedia
- Artiodactyla: even-toed ungulates, cattle, sheep, goats, pigs, antelope, and many others
- Cetacea: whales and dolphins (which evolved from hoofed land animals)
- Perissodactyla: odd-toed ungulates such as horses and rhinos
- Proboscidea: elephants
- Sirenia: dugongs and manatees
- Hyracoidea: hyraxes
- Tubulidentata: aardvarks
Cetacea and Artiodactyla are thought to be closely related, and to form the Cetartiodactyla. The Hyracoidea, Perissodactyla and the Tethytheria (Proboscidea and Tethytheria) are the Altungulata. The Tubulidentata are also thought to be Ungulates.
That these groups of mammal are most closely related to each other has occasionally been questioned on anatomical and genetic grounds. Molecular phylogenetic studies have suggested that Perissodactyla and Cetartiodactyla are closest to Carnivora and Pholidota rather than to Hyracoidea, Tubulidentata, Sirenia and Proboscidea.
The Macroscelidea have been interpreted as Ungulates, and there is dental evidence supporting this interpretation. Suggestions that Cetaceans and Hyracoids are not closest to at least some other ungulates are out of favour, and so is the suggestion that the aardvark is related to South American Xenarthrans.
Most large land mammals are ungulates.
Ungulate groups represented in the fossil record include the Embrithopods, Desmostylians and various South American and Paleogene lineages.
In addition to hooves, ungulates developed reduced canine teeth, bunodont molars (molars with low, rounded cusps), and an astragalus (one of the ankle bones at the end of the lower leg) with a short, robust head.
Ungulates diversified rapidly in the Eocene, but are thought to date back perhaps as far as the late Cretaceous. Most ungulates are herbivores, but a few are omnivores or predators (for example, whales).
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