earlier litopterns Theosodon, Cramauchenia or Promacrauchenia, or a similar species. Litopterna was one of the five (four in some classifications) ancient orders of endemic South American mammals collectively called meridiungulates. Their relationships with other mammal groups outside South America have been poorly understood, as their early evolutionary history would have been in Western Gondwana, and outside of South America this area is now Antarctica. When South America separated from Antarctica in the Eocene, meridungulate orders survived in South America in isolation. Most flourished in the Paleogene and then diminished. Formerly, North American paleontologists considered them inferior to Northern Hemisphere taxa and to have been outcompeted to extinction in the Great American Biotic Interchange after the establishment of the Central American land bridge. However, more recent evidence shows that three of the meridungulate orders declined long before, just as happened to early mammal groups elsewhere. Litopterns and notoungulates continued, evolving into a variety of more derived forms. While toxodontid notoungulates expanded into North America during the GABI, litopterns remained confined to South America. Macrauchenia was among the last surviving meridungulates, along with litopterns such as Macraucheniopsis, Neolicaphrium, and Xenorhinotherium and the large notoungulates Piauhytherium, Trigodonops, Toxodon, and Mixotoxodon. These last endemic South American hoofed animals died out at the end of the Lujanian (10,000-20,000 years ago). Sequencing of mitochondrial DNA extracted from an M. 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 sixty-six million years ago. Analysis of collagen sequences obtained from Macrauchenia and Toxodon reached a similar conclusion and extended membership in the sister group clade to notoungulates. Description Macrauchenia had a somewhat camel-like body, with sturdy legs, a long neck and a relatively small head. Its feet, however, more closely resembled those of a modern rhinoceros, with one central toe and two side toes on each foot. It was a large animal, with a body length of around and a weight up to , about the size of a black rhinoceros. One striking characteristic of Macrauchenia is the openings for the nostrils on top of the head, above and between the eyes. Increasingly retracted nostrils are an evolutionary trend in later litopterns. Because mammals with trunks show the nostrils in a similar position, a popular hypothesis is that Macrauchenia had a trunk similar to a tapir or an inflated snout