Ungulate: Encyclopedia II - Ungulate - Relationships

Ungulate - Relationships

The Perissodactyla and Artiodactyla make up the largest portion of ungulates, and also comprise the majority of large land mammals. These two groups first appeared during the late Paleocene and early Eocene (about 54 million years ago), rapidly spreading to a wide variety of species on numerous continents, and have developed in parallel since that time.

Although whales and dolphins (Cetacea) do not posess most of the typical morphological characteristics of ungulates, recent discoveries have suggested that they are likely descended from early artiodactyls, and thus are directly related to other even-toed ungulates such as cattle and hippopotamuses. (As a result of these discoveries, a new order of Cetartiodactyla has also been proposed to include the members of Artiodactyla and Cetacea, to reflect their common ancestry.)

The Hyracoidea, Sirenia and Proboscidea are the Paenungulata. The Tubulidentata are also thought to be Ungulates. The Macroscelidea have been interpreted as Ungulates, and there is dental evidence supporting this interpretation. The Macroscelidea and Tubilidentata have recently been united with the Paenungulata in the Pseudungulata.

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.

Ungulate groups represented in the fossil record include the Embrithopods, Demostylians, Mesonychids, Condylarths and various South American and Paleogene lineages.

In addition to hooves, most 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 as far as the late Cretaceous. Most ungulates are herbivores, but a few are omnivores or even predators: the Mesonychia and whales.

Adapted from the Wikipedia article "Relationships", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki