The fauna of Puerto Rico is similar to other island archipelago faunas, with high endemism, and low, skewed taxonomic diversity. Bats are the only extant native terrestrial mammals in Puerto Rico. All other terrestrial mammals in the area were introduced by humans, and include species such as cats, goats, sheep, the small Indian mongoose, and escaped monkeys. Marine mammals include dolphins, manatees, and whales. Of the 349 bird species, about 120 breed in the archipelago, and 47.5% are accidental or rare.
The most recognizable and famous animal of Puerto Rico is probably the common coquí, a small endemic frog, and one of the 86 species that constitute Puerto Rico's herpetofauna. Some native freshwater fish inhabit Puerto Rico, but some species, introduced by humans, have established populations in reservoirs and rivers. The low richness-high diversity pattern is also apparent among invertebrates, which constitutes most of the archipelago's fauna.
The arrival of the first people about 4,000 years ago and of Europeans more than 500 years ago, had a significant effect on Puerto Rico's fauna. Hunting, habitat destruction, and the introduction of non-native species to Puerto Rico led to extinctions and extirpations (local extinctions). Conservation efforts, the most notable being for the Puerto Rican parrot, began in the second half of the 20th century. According to IUCN, as of 2002, there were 21 threatened species in Puerto Rico: two mammals, eight breeding birds, eight reptiles, and three amphibians.
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.
