Litopterna

Litopterna was an extinct order of hoofed mammals native to South America, living from the Paleocene to the late Pleistocene. Its members included long-legged runners and forms with distinctive, reduced toe counts.

South American native ungulates: An informal grouping of hoofed mammals that evolved in isolation in South America before major interchange with North America. Litopterns were one of several endemic hoofed-mammal lineages on the continent.
Mesaxonic foot: A foot whose central third digit forms the main axis of support. Several litopterns reduced their toes until the central digit bore most of the body's weight.
Macrauchenia: A large, long-necked South American litoptern that survived into the late Pleistocene. Its elongated limbs and unusual skull make it the best-known late-surviving litoptern.
Paleocene: The first geological epoch of the Paleogene, lasting from about 66 to 56 million years ago. Litopterns appeared in South America during this early post-dinosaur interval.
Meridiungulata: A proposed grouping of extinct South American hoofed-mammal orders, including Litopterna and Notoungulata. Litopterns are often discussed within this assemblage, whose evolutionary unity remains uncertain.
Ungulate: A mammal belonging to a broad group traditionally characterized by hoofed feet. Litopterns were hoofed mammals, though their evolutionary relationship to living ungulates remains debated.
Monodactyl: Having a single functional digit on each foot. Macrauchenia and some close relatives carried their weight on one digit per foot.
Macraucheniidae: A family of litopterns that included Macrauchenia and other long-limbed forms. This family represents the order's best-known late Cenozoic radiation.
Great American Biotic Interchange: The exchange of terrestrial animals between North and South America after the formation of the Isthmus of Panama. The interchange brought new competitors and predators into South America near the end of litoptern history.
Notoungulata: An extinct order of South American hoofed mammals with a diverse range of body forms. It is another major endemic ungulate lineage whose relationship to Litopterna is debated.

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