THE GENESIS OF CENTRAL-AMERICA - BIOLOGY VERSUS GEOPHYSICS

The predominant geophysical theory for the origin of Central America proposes that, in the Cretaceous-Paleocene, the Caribbean Plate migrated from the Eastern Pacific to the Western Atlantic. As it did so, it supposedly pushed the original Central American archipelago eastward to form the Antillean chain. This would have left an oceanic gap between the Americas that lasted some 60 million years. Palaeontological and neontological research now indicate that a variety of terrestrial and freshwater animals must have been able to disperse between North and South America during the time of the oceanic gap. The disharmonic composition and apparent later origin of the antillean faunas suggest that the Greater Antilles-Aves Ridge was not available as a dispersal corridor in the Cretaceous-Paleocene. Work on the Cretaceous marine bivalve fauna indicated the gradual development of a terrestrial Central American barrier during that Period. By the latest Cretaceous, the faunas of the eastern and western sides appear to have become well separated. This suggests an in situ formation of Central America, probably as the result of interaction between the Caribbean, Cocos, and Nazca plates. This theory is consistent with the evidence of terrestrial dispersals, marine bivalve separation, and the relatively old age of the Central American biota.