The Litopterns probably became stranded in South America after it broke away from the rest of the world during the end of the Eocene, 35 MYA. The Litopterns survived there in isolation for most of the Cenozoic, but when during the Pliocene South America connected with North America, starting the Great Faunal Interchange, the Litopterns began to decline, and by 20 000 years ago, during the Pleistocene, they all died out.