The Origins of Platyrrhine Monkeys in South America
The origin of monkeys on the continent of South America is a matter of much current debate. Given the isolation of South America for a large time during the Tertiary Period, the question of how the monkeys reached the continent may be difficult to answer. The two most likely places of where platyrrhines originated from are North America and Africa, Antarctica being a third place would be difficult to discern because of the difficulty in finding fossils in such a harsh land.
The South American continent became separated from Africa during the Mesozoic era, so the problem is how did the primates reach the continent. The first fossil primates were found in the late Oligocene and South America was not much closer to either Africa or North America as it is today. The early thinking by scientists was that the primates rafted from North America to South America, but new evidence points to a probable African origin of platyrrhine monkeys.
There is much evidence that would show an African origin of the platyrrhine monkeys of South America. First the ocean currents of that time would have facilitated a crossing from Africa to South America and not from North America (Tarling, 1982; cited in Fleagle, 1988). During the middle Oligocene there was a large drop in sea level that may have allowed rafting to be more permissible (Fleagle, 1988). The first fossil platyrrhine, Branisella boliviana was found during the late Oligocene, so it is possible that platyrrhines first came to South America during the middle Oligocene (Fleagle, 1988). Also there is a morphological characteristic that links the platyrrhines with the Oligocene parapithecids of Africa. Both the parapithecids and extinct and extant platyrrhines show extensive postorbital closure, which is not found in primates from North America (Fleagle and Kay, 1997). The caviamorph rodents that are found in South America also did not appear until the Oligocene and have their closest relatives as the African porcupines showing that there may have been other animals rafting from Africa to South America (Hoffstetter and Lavocat, 1970; cited in Fleagle, 1988).
As for the theory that platyrrhines may have come from North America, there are no non-tarsier haplorrhines that are found in North America. If platyrrhines would have come from North America then there would have had to have been a separate strepsirrhine origin which is probably unlikely (Fleagle, 1988). Thus most of the evidence for the origin of platyrrhines points to the continent of Africa (Fleagle, 1988).
Fleagle, J.G. 1988. Primate Adaptation and Evolution. Academic Press: New York.
Fleagle, J.G. and Kay, R.F. 1997. Platyrrhines, Catarrhines, and the Fossil Record. In New World Primates: Ecology, Evolution, and Behavior. Ed. W.G. Kinzey. Aldine de Gruyter: New York.
Hoffstetter, R. and Lavocat, R. 1970. Decouverte dans le Deseadien de Bolivie de Genres Pentalophodentes Appuyant les Affinites Africaines des Rongeurs Caviomorphes. C. R. Acad. Sci. (Paris), ser D., Vol. 271, 172-175.
Tarling, D.H. 1982. Land Bridges and Plate Tectonics. In Phylogenie et Paleobiogeographie. Eds. E. Buffetaut, P. Janvier, J.C. Rage, and P. Tassy. Geobios, Mem. Spec., Vol. 6, 361-374.