(A) Theosodon, (B) Scalabrinitherium, (C) Macrauchenia, portraying how the nasal bones shifted backwards on the skull, with the nasal opening following suit.
The family Macraucheniidae includes genera such as Theosodon, Xenorhinotherium, and Macrauchenia. Macrauchenia is the best-known and most recent macraucheniid. It became extinct during the PleistoceneEpoch. It was one of the few litopterns to survive the ecological pressures of the Great American Interchange between North and South America, which took place after the Isthmus of Panama rose above sea level some 3 million years ago. It may instead have died out in the aftermath of the invasion of the Americas by human hunters. When Macrauchenia died out, so too did Macraucheniidae and the entire litoptern order.
Sequencing of mitochondrial DNA extracted from a Macrauchenia patachonica fossil from a cave in southern Chile indicates that Macrauchenia (and by inference, Litopterna) is the sister group to Perissodactyla, with an estimated divergence date of 66 million years ago.[6] Analysis of collagen sequences obtained from Macrauchenia and Toxodon gave the same conclusion, adding notoungulates to the sister group clade.[7][8]