Ungulate
From Freepedia
Ungulates (meaning roughly "hoofed" or "hoofed animal") make up several orders of mammals, of which six to eight survive:
- Artiodactyla: even-toed ungulates, such as cattle, sheep, goats, pigs, antelope, and many others
- Cetacea: whales and dolphins
- Perissodactyla: odd-toed ungulates such as horses and rhinos
- Proboscidea: elephants
- Sirenia: dugongs and manatees
- Hyracoidea: hyraxes
- Tubulidentata: aardvarks
Relationships
Cetacea and Artiodactyla are thought to be closely related, and to form the Cetartiodactyla. 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.
Most large land mammals are ungulates.
Ungulate groups represented in the fossil record include the Embrithopods, Demostylians, Mesonychids, Condylarths 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 as far as the late Cretaceous. Most ungulates are herbivores, but a few are omnivores or even predators: the Mesonychia and whales.
Recent Developments
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 the Pseudungulata.
The Pseudungulata are by some scientists united with the Afrosoricida in the cohort or super-order Afrotheria based on molecular and DNA analysis. This means they are not related to other ungulates.
The extinct South-American ungulates, evolved when the continent was in isolation, are united in the super-order Meridiungulata. They are by some thought to be unrelated to the other ungulates. Instead, they are united with the Afrotheria and the Xenarthra in the supercohort Atlantogenata.
The position of other extinct ungulates is unclear. Embrithopods, Desmostylians and other related groups are seen as relatives of the Paenungulata, thus members of the Afrotheria. The Condylarths are, as a result, no longer seen as the ancestors of all ungulates. Instead, it is now believed the condylarths are members of the cohort Laurasiatheria. So it seems that, of all the ungulates, only the Perissiodacyla and Artiodactyla descended from the condylarths.
As a result of all this, it seems the typical Ungulate morphology originated three times independantly: in the Meridiungulata, the Afrotheria and the "true" ungulates in the Laurasiatheria. A great example of convergent evolution. This is met with scepticism by some scientists, who say there is no morphological evidence to split the ungulates up in so many unrelated clades.
