DISPERSAL AND EVOLUTION OF THE CUBAN CROCODILE (CROCODYLIDAE: CROCODYLIFORMES) IN THE CIRCUM-CARIBBEAN USING BIOGEOGRAPHY AND BONE COLLAGEN STABLE ISOTOPES

The Cuban crocodile (Crocodylus rhombifer) was once widespread throughout the circum-Caribbean with fossil localities in The Bahamas, Cuba, and Grand Cayman. Today the species is considered critically endangered by the International Union for Conservation of Nature and Natural Resources and wild populations only exist in two localities in Cuba. The combined population of the species is estimated at around 4,000 individuals. A previous study of bone collagen from Quaternary fossils from a bluehole in The Bahamas tested for terrestriality in C. rhombifer from specimens that dated to before human occupation. The study found strong similarity between the δ¹⁵N and δ¹³C of Bahamian C. rhombifer and terrestrial carnivores, whereas marine carnivores consistently had values much more concentrated. This suggested that C. rhombifer was a terrestrial predator and less adapted to marine life. Given the terrestrial preference of C. rhombifer, this provides new insight into its timing and dispersal of this endangered species. Following molecular studies, C. rhombifer likely shares a closer relationship with the less marine-adapted Crocodylus moreletii of the Yucatan than the more marine-adapted and widely dispersed Crocodylus acutus. Occurrences of most terrestrial vertebrates of the Caribbean have been accounted for by following a much more eastern land/island-based dispersal route from eastern South America, summarized as the GAARlandia hypothesis (GAAR refers to the Greater Antilles and Aves Ridge). Given the complete lack of fossil evidence from northern South America of C. rhombifer and C. moreletti, this dispersal hypothesis seems unlikely to account for C. rhombifer in the circum-Caribbean. Although not conflicting with this hypothesis, bathymetry and timing of fossil occurrences are more consistent with dispersal from the Yucatan Peninsula. This dispersal would have brought the ancestor of C. rhombifer through Cuba, and radiated out toward The Bahamas to the north, and likely along a natural ridge extending west from southern Cuba toward Grand Cayman. We suggest possible shortened and shallower passageways prior to the earliest fossil occurrences of Crocodylus in the Caribbean as an alternative route for Crocodylus to that of the South American starting point of the GAARlandia hypothesis.