Résumé
The fossil record can provide direct evidence for how modern and past terrestrial biodiversity originated and accumulated over time and space. This is of particular interest in regions with high species richness and endemism threatened by extinction today, as these vulnerable ecosystems are often considered the result of evolutionary processes operating over long-time scales. Oceanic islands provide unique insight to tempo and mode of evolution in relatively closed ecosystems with low immigration rates and high in situ species origination. Classic studies on extant vertebrates in the Caribbean region suggested that the islands have not only acted as museums that retain representatives of ancient lineages, but also were centers of large endemic radiations. While the late Quaternary terrestrial fossil record of the archipelago is well known and documents significant extinctions and extirpations associated with the arrival of humans in the region, the pre-Quaternary record is relatively limited. Even with this limited record, it is clear that a significant portion of extant and recently extinct Caribbean taxa (e.g., lizards in the genera Anolis and Sphaerodactylus, frogs of the genus Eleutherodactylus, sloths, primates, and caviomorph rodents) were already in the Caribbean by the early Miocene, while a few other clades colonized the islands and became extinct before the Quaternary. Recent fieldwork in two Late Miocene-Early Pliocene (7.14–4.57 mya) fossil rich localities in northeast Hispaniola has revealed the presence of a unique and distinct terrestrial faunal assemblage. At least 14 vertebrate taxa were collected including a sloth, two rodents, a sirenian, a pelomedusoide turtle, a gharial, several indeterminate teleosts, four elasmobranchs as well as the first confirmed records of a caiman, sebecosuchian, and siluriform in the Caribbean islands. Fossil invertebrates including terrestrial and brackish water mollusks were also recovered in the stratigraphy, suggesting that the vertebrate bonebed was deposited in a salty marsh paleoenvironment which developed with varying degrees of open sea influence. While a previous study on sloth fossils from these localities suggested affinities to taxa from Cuba, at least six other vertebrate taxa correspond to groups that have no recent fossil record and are no longer present in the region today. The disappearance of these groups, particularly the predator guild between the Late Pliocene and Pleistocene not only suggests substantial changes to terrestrial ecosystems in Hispaniola, but that assembly of modern biodiversity was in part likely the result of post Pliocene radiations and colonization.