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Cladus: Eukaryota
Supergroup: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Classis: Mammalia
Subclassis: Theria
Infraclassis: Placentalia
Superordo: †Meridiungulata
Ordo: Litopterna
Familiae: Protolipternidae - Macraucheniidae - Notonychopidae - Adianthidae - Proterotheriidae


Litopterna Ameghino, 1889

Vernacular names
English: Litopterns
日本語: 滑距目
Português: Litopternos


Litopterna ("simple ankles") is an extinct order of fossil hoofed mammals (ungulates) from the Tertiary period that displays toe reduction. Three-toed, and even a one-toed horselike form developed.

This order, known only from South America, was common and varied in early faunas and persisted, in decreasing variety, into the Pleistocene. Early forms are near the condylarths, to such an extent that the litopterns might be considered merely as surviving and diversely specialized condylarths. They are suspected of being descended from South American condylarths, and therefore to have the same source as the latter. However, there is a growing number of scientists who believes the Litopterna (together with other South-American ungulates) originated completely independent from the other ungulates, thus are unrelated to the condylarths. They proposed a new clade to contain these groups: the Meridiungulata. Macrauchenia was the youngest genus of litopterns, and was the only litoptern group to survive the Great American Interchange; it died out during the Pleistocene.

The Litopterna, like the notoungulates and pyrotheres, are examples of ungulate mammals that arose relatively independently in "splendid isolation" on the island continent of South America. Like Australia, South America was isolated from all other continents following the breakup of Gondwana. During this period of isolation, unique mammals evolved to fill ecological niches similar to other mammals elsewhere. The Litopterna occupied ecological roles as browsers and grazers similar to horses and camels in Laurasia.

* McKenna, M. C, and S. K. Bell. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp.

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Source: Wikispecies, Wikipedia: All text is available under the terms of the GNU Free Documentation License