Origin of Puerto Rican Fauna
The Caribbean Plate, an oceanic tectonic plate on which Puerto Rico and the Antilles (with the exception of Cuba) lie, was formed in the late Mesozoic. According to Rosen, when South America separated from Africa, a volcanic archipelago known as "Proto-Antilles" was formed. It later divided into the present-day Greater and Lesser Antilles because of a new fault line in the "Proto-Antilles". Geologically, the archipelago of Puerto Rico is young, having formed about 135 Ma (million years) ago. The prevailing hypothesis, proposed by Howard Meyerhoff, posits that the Puerto Rican Bank, consisting of Puerto Rico, its outlying islands, and the Virgin Islands with the exception of St. Croix, was formed from volcanism in the Cretaceous Period. Rock samples from Sierra Bermeja in southwestern Puerto Rico, dated to the late Jurassic/early Cretaceous period, confirm this theory.
There is ongoing debate over when and how the ancestors of vertebrate fauna colonized the Antilles—particularly whether the Proto-Antilles were oceanic islands or whether they once formed a land connection between South and North America. The first, and prevailing, model favors overwater dispersal from continental, primarily South American, fauna; the other suggests the vicarization of proto-Antillean fauna. Hedges et al. conclude that dispersal was "the primary mechanism for the origin of West Indian biota". Vertebrate terrestrial genera such as Eleutherodactylus dispersed in a "filter" effect among the islands before any vicarization event occurred. However, other fauna such as the endemic Antillean insectivores (Nesophontes sp., Solenodon marcanoi and others) and freshwater fish appear to have colonized the West Indies earlier through other means. Woods provides evidence to support this hypothesis by analyzing the arrival of ancestors of the Antillean capromyids and echimyids, concluding that an ancient echimyid must have arrived on the Greater Antilles from South America either by island-hopping through the Lesser Antilles or by rafting either to Puerto Rico or Hispaniola.
MacPhee and Iturralde provide an alternate hypothesis that the initiators of land mammal clades arrived on the Proto-Antilles by the mid-Tertiary period, approximately at the Eocene–Oligocene boundary. A short-lived (~1 Ma) landmass named "GAARlandia" (Greater Antilles + Aves Ridge land) connected northwestern South America with three of the Greater Antilles (Cuba, Hispaniola and Puerto Rico) during this period. Afterwards, during the fragmentation of the Proto-Antilles, divergence of vacariated lines would have begun.
The last major changes in Puerto Rican fauna occurred about 10,000 years ago as a result of the post-Ice Age rise in sea level and associated environmental changes. Puerto Rico's transformation from a dry savanna environment to its present moist, forested state led to mass extinctions, especially of the vertebrate fauna. Around this time, the Puerto Rican Bank—a single landmass comprising the archipelago of Puerto Rico (except for Mona, Monito and Desecheo) and the Virgin Islands (except for St. Croix)—became separated. The Puerto Rican Bank has never been connected to its closest eastern bank, St. Maarten.
Read more about this topic: Fauna Of Puerto Rico
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