The fauna of the West Indies includes more than 1300 native terrestrial vertebrate species and is characterized by high levels of endemism. Several theories have been proposed to explain how these animals arrived to the islands, including dispersal, vicariance, and land bridges. The dispersal theory proposes that most of the West Indian terrestrial biota arrived by flying or by flotsam. The vicariance theory suggests that there was a proto-Antillean land mass, or masses, connecting North and South America in the late Cretaceous that traveled eastward as the Caribbean geologic plate developed and carried an ancient biota with it. One widely discussed land bridge theory proposes that much of the Antillean biota originated by dispersal over an unbroken dry land connection, the Aves Ridge, between South America and the Greater Antilles 35–33 Ma. Geologic evidence cannot unambiguously support or refute any of these models, despite claims to the contrary. Other evidence bearing on these three theories, or mechanisms, comes from the taxonomic composition of the fauna, their phylogenetic relationships, fossil record, paleogeography, ecology, climate, water currents, and divergence time estimates from molecular clocks. This evidence supports an origin by overwater dispersal for most or all of the West Indian terrestrial vertebrate fauna. The strongest support comes from a reduced higher-level taxonomic composition of the fauna (now and in the past), the presence of unusually large adaptive radiations, and the finding of divergence time estimates between island and mainland groups that are not clustered around a particular time. In addition, the majority of terrestrial (non-flying) groups have closest relatives in South America, which is consistent with the direction of water currents and most hurricane tracks. Some of the same evidence in support of dispersal argues against a mid-Cenozoic land bridge from South America. Several ancient, relictual groups (e.g., xantusiid lizards and solenodontoid shrews) may have arisen through proto-Antillean vicariance, and molecular clock analyses—here revisited—provide support for this, but an origin by dispersal can also be argued. No model can be completely discounted. Although the general pattern (dispersal) has emerged, many details remain to be determined concerning the origin of the fauna.
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