[2] Around the middle of the Cenozoic, approximately 34 million years ago,[3] two types of mammals appeared for the first time in South America: rodents and primates.
Both of these groups had already been inhabiting other continents for millions of years and they simply arrived in South America rather than originated there.
Therefore, the most likely explanation is that they somehow crossed the Atlantic Ocean, which was less wide than today, landed in South America, and founded new populations of rodents and primates.
[4] The first South American primates gave rise to an impressive evolutionary radiation: more than 120 species in five families.
[7] Note: some authors, among others Fossilworks, consider Killikaike synonymous with Homunculus and Szalatavus with Branisella, while other researchers consider the genera as different.The Panamanian and Caribbean fossil primates have been included for completeness.