The origin and affinities of the South American Condylarthra and early Tertiary Litopterna (Mammalia). American Museum novitates ; no. 2772

49 p. : ill. ; 26 cm.Includes bibliographical references (p. 42-49)."A previously unknown genus and species of a primitive litoptern from the late Paleocene (Riochican) of Itaboraí, Brazil, is described, and three previously described didolodontid and litoptern species from Itaboraí are referred to new genera. Comparative analysis of the dentition of didolodontids and primitive Litopterna suggests a number of revisions in their taxonomy. The two Itaboraí didolodonts appear to be more closely related to each other than to Patagonian forms; Protolipterna, new genus, Miguelsoria, new genus, ?and Asmithwoodwardia are placed in the Litopterna in a new family, Protolipternidae. Anisolambda (including Ricardolydekkeria and Josepholeidya) and allies seem to be related to true proterotheriids, and are placed in the Proterotheriidae in a new subfamily, Anisolambdinae, whereas the Polymorphinae (including only the type genus) appears to be related to the Macraucheniidae. Proectocion (including Oxybunotherium), previously referred to the Didolodontidae, is placed in the advanced litoptern family Adianthidae. An ancestral morphotype for the Litopterna and Didolodontidae is constructed on the basis of their known morphology and by comparison with primitive oxyclaenine arctocyonids such as Protungulatum. Relevant North American ungulate families (Arctocyonidae, Hyopsodontidae, Phenacodontidae, Periptychidae) are briefly reviewed and their members compared with this hypothetical ancestor. The primitive litoptern/didolodont morphotype is closely comparable to and shares derived conditions with Torrejonian mioclaenine hyopsodonts such as Litaletes. Such an exclusive relationship implies that the indigenous South American ungulate orders may not represent a strictly monophyletic unit with respect to other Eutheria"--P. [1]