Early Oligocene chinchilloid caviomorphs from Puerto Rico and the initial rodent colonization of the West Indies.

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)).

New record of Neosaimiri (Cebidae, Platyrrhini) from the late Middle Miocene of Peruvian Amazonia.

The Honda Group of La Venta, Colombia, has yielded a wide array of crown platyrrhine primates, documenting the late Middle Miocene epoch (ca. 13.1-12.6 Ma, Laventan South American Land Mammal Age). Although exceptional, this record represents only a snapshot of the evolutionary history of New World monkeys because virtually none of the primate taxa recorded at La Venta had so far been found elsewhere. We describe here few dental remains of a cebine platyrrhine discovered from Laventan deposits in the San Martín Department of Peru (Peruvian Amazonia). The primate dental specimens from that new fossil-bearing locality (TAR-31) are strongly reminiscent morphologically of the teeth of Neosaimiri fieldsi from La Venta. However, given that several aspects of the dental variability from TAR-31 are unknown, we prefer to provide an assignment with open nomenclature (i.e., N. cf. fieldsi), instead of formally referring these remains to N. fieldsi, pending the discovery of additional specimens. The occurrence of Neosaimiri in Peru, in coeval deposits of La Venta, thus represents a second and southernmost record of that low-latitude genus in the Neotropics, thereby demonstrating its wide distribution along the northwestern edge of the Pebas Mega-Wetland System, in tropical western South America.

Neotropics provide insights into the emergence of New World monkeys: New dental evidence from the late Oligocene of Peruvian Amazonia.

Recent field efforts in Peruvian Amazonia (Contamana area, Loreto Department) have resulted in the discovery of a late Oligocene (ca. 26.5 Ma; Chambira Formation) fossil primate-bearing locality (CTA-61). In this paper, we analyze the primate material consisting of two isolated upper molars, the peculiar morphology of which allows us to describe a new medium-sized platyrrhine monkey: Canaanimico amazonensis gen. et sp. nov. In addition to the recent discovery of Perupithecus ucayaliensis, a primitive anthropoid taxon of African affinities from the alleged latest Eocene Santa Rosa locality (Peruvian Amazonia), the discovery of Canaanimico adds to the evidence that primates were well-established in the Amazonian Basin during the Paleogene. Our phylogenetic results based on dental evidence show that none of the early Miocene Patagonian taxa (Homunculus, Carlocebus, Soriacebus, Mazzonicebus, Dolichocebus, Tremacebus, and Chilecebus), the late Oligocene Bolivian Branisella, or the Peruvian Canaanimico, is nested within a crown platyrrhine clade. All these early taxa are closely related and considered here as stem Platyrrhini. Canaanimico is nested within the Patagonian Soriacebinae, and closely related to Soriacebus, thereby extending back the soriacebine lineage to 26.5 Ma. Given the limited dental evidence, it is difficult to assess if Canaanimico was engaged in a form of pitheciine-like seed predation as is observed in Soriacebus and Mazzonicebus, but dental microwear patterns recorded on one upper molar indicate that Canaanimico was possibly a fruit and hard-object eater. If Panamacebus, a recently discovered stem cebine from the early Miocene of Panama, indicates that the crown platyrrhine radiation was already well underway by the earliest Miocene, Canaanimico indicates in turn that the "homunculid" radiation (as a part of the stem radiation) was well underway by the late Oligocene. These new data suggest that the stem radiation likely occurred in the Neotropics during the Oligocene, and that several stem lineages independently reached Patagonia during the early Miocene. Finally, we are still faced with a "layered" pattern of platyrrhine evolution, but modified in terms of timing of cladogeneses. If the crown platyrrhine radiation occurred in the Neotropics around the Oligocene-Miocene transition (or at least during the earliest Miocene), it was apparently concomitant with the diversification of the latest stem forms in Patagonia.

Late middle Miocene caviomorph rodents from Tarapoto, Peruvian Amazonia.

Miocene deposits of South America have yielded several species-rich assemblages of caviomorph rodents. They are mostly situated at high and mid- latitudes of the continent, except for the exceptional Honda Group of La Venta, Colombia, the faunal composition of which allowed to describe the late middle Miocene Laventan South American Land Mammal Age (SALMA). In this paper, we describe a new caviomorph assemblage from TAR-31 locality, recently discovered near Tarapoto in Peruvian Amazonia (San Martín Department). Based on mammalian biostratigraphy, this single-phased locality is unambiguously considered to fall within the Laventan SALMA. TAR-31 yielded rodent species found in La Venta, such as the octodontoid Ricardomys longidens Walton, 1990 (nom. nud.), the chinchilloids Microscleromys paradoxalis Walton, 1990 (nom. nud.) and M. cribriphilus Walton, 1990 (nom. nud.), or closely-related taxa. Given these strong taxonomic affinities, we further seize the opportunity to review the rodent dental material from La Venta described in the Ph.D. volume of Walton in 1990 but referred to as nomina nuda. Here we validate the recognition of these former taxa and provide their formal description. TAR-31 documents nine distinct rodent species documenting the four extant superfamilies of Caviomorpha, including a new erethizontoid: Nuyuyomys chinqaska gen. et sp. nov. These fossils document the most diverse caviomorph fauna for the middle Miocene interval of Peruvian Amazonia to date. This rodent discovery from Peru extends the geographical ranges of Ricardomys longidens, Microscleromys paradoxalis, and M. cribriphilus, 1,100 km to the south. Only one postcranial element of rodent was unearthed in TAR-31 (astragalus). This tiny tarsal bone most likely documents one of the two species of Microscleromys and its morphology indicates terrestrial generalist adaptations for this minute chinchilloid.