By their past and present diversity, rodents are among the richest components of Caribbean land mammals. Many of these became extinct recently. Causes of their extirpation, their phylogenetic affinities, the timing of their arrival in the West Indies and their biogeographic history are all ongoing debated issues. Here, we report the discovery of dental remains from Lower Oligocene deposits ( ca 29.5 Ma) of Puerto Rico. Their morphology attests to the presence of two distinct species of chinchilloid caviomorphs, closely related to dinomyids in a phylogenetic analysis, and thus of undisputable South American origin. These fossils represent the earliest Caribbean rodents known thus far. They could extend back to 30 Ma the lineages of some recently extinct Caribbean giant rodents ( Elasmodontomys and Amblyrhiza ), which are also retrieved here as chinchilloids. This new find has substantial biogeographic implications because it demonstrates an early dispersal of land mammals from South America to the West Indies, perhaps via the emergence of the Aves Ridge that occurred ca 35–33 Ma (GAARlandia hypothesis). Considering both this new palaeontological evidence and recent molecular divergence estimates, the natural colonization of the West Indies by rodents probably occurred through multiple and time-staggered dispersal events (chinchilloids, then echimyid octodontoids (spiny rats/hutias), caviids and lastly oryzomyin muroids (rice rats)).

This contribution provides the raw files for the µCT-scan data and renderings of the three-dimensional digital models of two fossil teeth of a geomyin geomorph rodent (Caribeomys merzeraudi), discovered from lower Oligocene deposits of Puerto Rico, San Sebastian Formation (locality LACM Loc. 8060). These fossils were described, figured and discussed in the following publication: Marivaux et al. ( 2021), An unpredicted ancient colonization of the West Indies by North American rodents: dental evidence of a geomorph from the early Oligocene of Puerto Rico. Papers in Palaeontology.

El depósito paleontológico Las Llanadas es un manantial con sedimento rico en materia orgánica. Estudios del sitio a principios del siglo XX, dieron a conocer materiales fósiles de perezosos, cocodrilos, tortugas terrestres, y jutías. Dos especies de perezosos, Acratocnus antillensis y Neocnus gliriformis, fueron nuevas para la ciencia. En el presente trabajo se dan a conocer nuevos registros fósiles de anuros, un reptil y aves para el depósito: Peltophryne empusus, Osteopilus septentrionalis, Cyclura nubila, Tyto alba, Buteogallus borrasi y Boromys ofella. Huesos recientes de Lithobates catesbeianus y Capromys pilorides se encontraron entre los materiales, lo que indica que el depósito se mantiene activo en la recepción de especímenes. De un total de 2030 piezas solo 3% pudo ser identificado taxonómicamente, debido al alto nivel de fragmentación.