Mammal size shows that there was likely no archipelago in southern Central America during the Miocene.

The formation of the Isthmus of Panama during the latest Cenzoic was important event because it facilitated the mixing of terrestrial faunas between North and South America. Not since the late Cretaceous were terrestrial animals able to walk from North America to South America or vise versa. During the middle Cenozoic little is known of the paleogeography of southern Central America. For example did North America extend southward as an island arc system or as a peninsula. To investigate this question Michael Xavier Kirby from the Smithsonian Tropical Research Institute in Panama, and Bruce MacFadden from the University of Florida, measured specimens of mammals from the Gaillard Cut Local Fauna of the Cucaracha Formation in Panama and compared them with specimens of the same species from northern latitudes. They discovered no significant differences and concluded that in fact the Panama Canal Basin, was part of a peninsula rather than a series of islands.


Kirby, Michael Xavier and MacFadden, Bruce (2005) Was southern Central America an archipelago or a peninsula in the middle Miocene? A test using land-mammal body size, Palaeogeography, Palaeoclimatology, Palaeoecology, In Press, Corrected Proof, Available online 6 July 2005.