Litopterna

'' (Macraucheniidae) '' (Proterotheriidae) The body forms of many litopterns, notably in the limb and skull structure, are broadly similar to those of living ungulates, unlike other South American native ungulate groups, which are often strongly divergent from living ungulates. Members of the macraucheniid subfamily Macraucheniinae saw the progressive migration of the nasal opening to the top of the skull, which was often historically suggested to indicate the presence of a trunk, though other authors have suggested that a moose-like prehensile lip, or a saiga-like nose to filter dust are more likely. == Ecology ==

Litopterns were likely hindgut fermenters. At least some macraucheniids like Macrauchenia are suggested to have been mixed feeders feeding on both browse and grass. Sparnotheriodontids are suggested to have been browsers. Some proterotheriids are suggested to have been browsers, while some members proterotheriid subfamily Megadolodinae like Megadolodus have been suggested to have been omnivorous with at least part of their diet consisting of hard fruit. == Evolutionary history ==

Litopterna, like other "South American native ungulates" is thought to have originated from groups of archaic "condylarths" that migrated from North America. The relationship of Litopterna to other South American native ungulate groups is uncertain, though it may be closely related to the "condylarth" group Didolodontidae. Aside from South America, sparnotheriodontids are also known from the Eocene aged La Meseta Formation in the Antarctic Peninsula, representing the only record of litopterns on the Antarctic continent. Litopterns declined during the Pliocene and Pleistocene, likely as a result of climatic change and competition with recently immigrated North American ungulates who arrived as part of the Great American interchange, following the connection of the previously isolated North and South America via the Isthmus of Panama. It is possible that hunting had a causal role in their extinction. == Classification ==

• Order Litopterna • Proacrodon • Family Protolipternidae • Asmithwoodwardia • Miguelsoria • Protolipterna • Family Indaleciidae • ''''''''''Adiantoides • Indalecia • Family Sparnotheriodontidae • Phoradiadius • Notiolofos • Sparnotheriodon • Victorlemoinea • Family Amilnedwardsiidae • Amilnedwardsia • Ernestohaeckelia • Rutimeyeria • Family Notonychopidae • Notonychops • Requisia • Superfamily Macrauchenioidea • Family Adianthidae • Proectocion • Adianthinae • Adianthus • Proadiantus • Proheptaconus • Thadanius • Tricoelodus • Family Macraucheniidae • Llullataruca • Subfamily Cramaucheniinae • Coniopternium • Caliphrium • Cramauchenia • Phoenixauchenia • Polymorphis • Pternoconius • Theosodon • Subfamily Macraucheniinae • Cullinia • Huayqueriana • Macrauchenia • Macraucheniopsis • Oxyodontherium • Paranauchenia • Promacrauchenia • Scalabrinitherium • Windhausenia • Xenorhinotherium • Superfamily Proterotherioidea • Family Proterotheriidae • ''''''Anisolambda • Anisolophus • Brachytherium • Diadiaphorus • Diplasiotherium • Eoauchenia • Eolicaphrium • Epecuenia • Epitherium • Guilielmofloweria • Heteroglyphis • Lambdaconus • Lambdaconops • Mesolicaphrium • Neobrachytherium • Neodolodus • Neolicaphrium • Olisanophus • Paramacrauchenia • Paranisolambda • Picturotherium • Prolicaphrium • Promylophis • Proterotherium • Protheosodon • Pseudobrachytherium • Tetramerorhinus • Thoatherium • Thoatheriopsis • Villarroelia • Uruguayodon • Wainka • Xesmodon • Megadolodinae • Bounodus • Megadolodus == References ==