Suina (Gray, 1868)
The suborder Suina (also known as Suiformes) contains perhaps the earliest and most archaic even-toed ungulates
The suborder Suina includes the family Suidae (pigs, hogs) and the family Tayassuidae (peccaries). Some morphological studies also identified the family Hippopotamidae (hippopotami) among the Suina.
The oreodonts, a branch of the tylopoda, were often considered suines due to the popular, though inaccurate, description of them as "ruminating hogs". Oreodonts are not suines, but are more closely related to camels. However, the predators of the oreodonts, the entelodonts of the extinct family entelodontidae, are most likely suines. The peccaries and entelodonts seem to be closer related to each other than either is to modern pigs. In addition, as mentioned below, the Hippopotamus and the related anthracotheres may also not be suines.
Status of hippopotamidae
Hippopotamus were once thought to be part of the Suina, but a growing body of morphological and genetic evidence has suggested that they share a common ancestor not with Suina, but with Cetaceans—the Order which includes whales and dolphins. Whales and artiodactyls form a clade called Cetartiodactyla.
The most recent research into the origins of hippopotamidae suggests that hippos and whales shared a common semi-aquatic ancestor that branched off from other Artiodactyls around 60 million years ago. Descendants of this hypothesized ancestor likely split into two branches around 54 million years ago. One branch would evolve into cetaceans, possibly beginning with the proto-whale Pakicetus from 52 million years ago and other early whale ancestors, known as Archaeoceti, which eventually underwent aquatic adaptation into the almost completely aquatic cetaceans.
The anatomy of the Suina is different compared to other even-toed ungulates. For example, they have maxillary (upper) teeth in front, which allow for proper chewing of food. In contrast, other even-toed ungulates, such as goats and deer, have front teeth only on the bottom. This doesn't let them chew very well, thus they swallow and regurgitate their food to allow rumination.
Most even-toed ungulates have a four-chambered stomach. In contrast, the Suina have a simple stomach that allows an omnivorous diet.
1. ^ a b Boisserie, Jean-Renaud; Fabrice Lihoreau and Michel Brunet (February 2005). "The position of Hippopotamidae within Cetartiodactyla". Proceedings of the National Academy of Sciences 102 (5): 1537–1541. doi:10.1073/pnas.0409518102. PMID 15677331. PMC 547867. http://www.pnas.org/cgi/content/full/102/5/1537. Retrieved 2007-06-09.
Source: Wikispecies, Wikipedia: All text is available under the terms of the GNU Free Documentation License