Abstract
Mollusks fossil communities found is southerm Central America developed in accordance to tectonic, and hence favorable enviromental conditions of the Isthmus evolution. The initial stage of the island arc, during the Late Cretaceous, determined the apperance of rudistic bioherms on the shallow platforms surrounding the islands. Later, during the Early Tertiary the predominance of deeper sedimentary environments and the intensive volcanic activity restricted the mollusks populations to rather small groups.
During the Oligocene to Miocene, the island are evolved to a number of island of greater area separated by narrow channels. This provided an apropiate environment for the development of homogeneous malacological faunistic communities with hihg diversity of species. The final uplift of the Central America isthmus during the Pliocene stopped the faunistic intercahnge between Pacif and Caribeean communities which decrease diversification of species at the Caribeean side.