to perissodactyl and artiodactyl hoofed mammals in Laurasia. Litopterns were common and varied in early faunas and persisted, in decreasing variety, into the Pleistocene. Early forms were originally classified by European and North American paleontologists as closely related to condylarths, believed to be the order that gave rise to modern hoofed mammals. Litopterns were seen as persisting condylarths, primitive mammals that survived in isolation. "Condylarth" is now recognized as a wastebasket taxon for any generalized early mammal that wasn't obviously a predator, making this theory outdated. The modern version of the idea is that litopterns are a sister group of one of the ungulate taxa whose early fossils are found in Eurasia, meaning that all hoofed mammals share distant common ancestors. However, an opposing view has been that litopterns (together with other South-American ungulates) originated independently from ungulates on other continents, and thus are unrelated to all the groups once called condylarths, including the early perissodactyls and artiodactyls. In the independent-origin theory, litopterns are classified with other endemic South American ungulates as the clade Meridiungulata. Sequencing of mitochondrial DNA in 2017, extracted from a Macrauchenia patachonica fossil from a cave in southern Chile, indicates that Litopterna is the sister group to Perissodactyla, making litopterns true ungulates. The estimated divergence date is 66 million years ago. Analyses of collagen sequences obtained from Macrauchenia and the notoungulate Toxodon have led to the same conclusion, and add notoungulates to the sister group clade to litopterns. This idea contrasts with the results of some past morphological analyses which favoured them as afrotherians. It is consistent with some more recent morphological analyses which suggested they were basal ungulates. Panperissodactyla has been proposed as the name of an unranked clade to include perissodactyls and their extinct South American ungulate relatives. Taxonomy 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 References Further reading External links An artist's rendition of a Macrauchenia, a representative genus of the Litopterna. Retrieved from the Red Académica Uruguaya megafauna page Danian first appearances Holocene extinctions Fossil taxa described in 1889 Taxa named by Florentino