Historical biogeography of West Indian vertebrates

The vertebrate fauna of the West Indies (1262 species) exhibits high levels of endemism and has a taxonomic composition characteristic of more isolated oceanic islands. Many groups that are widespread on the mainland are absent in the islands, and some of those present are characterized by large adaptive radiations. The growing fossil record of West Indian vertebrates, including mid-Tertiary amber fossils (considered here to be 20-30 million years old), indicates that this pattern of reduced higher-taxon diversity has persisted for a long period of time. Phylogenetic relationships of nonvolant groups display a strong South American influence, whereas volant groups (birds and bats) and freshwater fish show closer ties with Central and North America. Molecular estimates of divergence times between island taxa and their mainland counterparts indicate a Cenozoic origin (within the last 65 million years) for nearly all groups examined. Together, data from different sources point to an origin by overwater dispersal for a large majority of the vertebrate fauna. The prevailing current direction, from southeast to northwest, and the wide scattering of estimated times of origin suggest that much of the nonvolant fauna arrived by flotsam carried from the mouths of major rivers in northeastern South America. Spatial relationships, especially considering low sea levels during the Pleistocene, appear to better explain the routes of colonization taken by the volant fauna and freshwater fish. Caribbean geologic history does not preclude an origin by late Mesozoic vicariance for several possibly ancient groups, although an early Cenozoic arrival by dispersal also cannot be discounted. An integrative approach to historical biogeography is shown to be more insightful than the current trend in the field, cladistic biogeography, which places prime emphasis only on phylogenetic relationships.