 Complete the following phrase:  It is likely that Macrauchenia evolved from earlier litopterns Theosodon 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 Meridungulates. 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 