Juan D. Carrillo

Neotropical mammal diversity and the Great American Biotic Interchange: spatial and temporal variation in South America's fossil record.

The vast mammal diversity of the Neotropics is the result of a long evolutionary history. During most of the Cenozoic, South America was an island continent with an endemic mammalian fauna. This isolation ceased during the late Neogene after the formation of the Isthmus of Panama, resulting in an event known as the Great American Biotic Interchange (GABI). In this study, we investigate biogeographic patterns in South America, just before or when the first immigrants are recorded and we review the temporal and geographical distribution of fossil mammals during the GABI. We performed a dissimilarity analysis which grouped the faunal assemblages according to their age and their geographic distribution. Our data support the differentiation between tropical and temperate assemblages in South America during the middle and late Miocene. The GABI begins during the late Miocene (~10–7 Ma) and the putative oldest migrations are recorded in the temperate region, where the number of GABI participants rapidly increases after ~5 Ma and this trend continues during the Pleistocene. A sampling bias toward higher latitudes and younger records challenges the study of the temporal and geographic patterns of the GABI.

Giant rodents from the Neotropics: diversity and dental variation of late Miocene neoepiblemid remains from Urumaco, Venezuela

Caviomorphs constitute a large evolutionary radiation of South America rodents, exhibiting a wide range of body size and ecomorphological disparity. The geological history of caviomorphs has been recorded mainly from high latitudes, besides isolated discoveries from the Neotropics. The late Miocene fauna from Urumaco, Venezuela, is noteworthy for its location and for preserving the giant rodent Phoberomys pattersoni. Previous studies of isolated postcranial remains suggested that the rodent diversity from Urumaco was higher than is currently recognized. Based on new remains we document dental variation that indicates the presence of at least two giant rodent taxa in Urumaco, including Neoepiblema. Quantitative analysis of dentition of the different neoepiblemid species supports the differentiation between Neoepiblema and Phoberomys and suggests that several recognized species of Phoberomys could represent different ontogenetic stages of one or few taxa within the genus.KurzfassungDie Caviomorpha stellen eine grosse evolutionäre Radiation südamerikanischer Nagetiere dar. Die geologische Geschichte der Caviomorpha ist, neben isolierten Entdeckungen in der Neotropis, hauptsächlich von den hohen Breiten überliefert. Die spätmiozäne Fauna von Urumaco, Venezuela, ist bemerkenswert für ihre Lage und für die Erhaltung von Phoberomys pattersoni. Vorhergehende Studien isolierter postcranialer Überreste deuteten darauf hin, dass die Diversität der Riesennager von Urumaco gröβer war als gegenwärtig angenommen. Basierend auf neuen Überresten dokumentieren wir dentale Variation, die auf die Anwesenheit von mindestens zwei verschiedenen Riesennager-Taxa in Urumaco, einschliesslich Neoepiblema, hinweist. Eine quantitative Analyse des Gebisses der verschiedenen neoepiblemiden Arten unterstützt die Unterscheidung zwischen Neoepiblema und Phoberomys, und deutet darauf hin, daβ verschiedene anerkannte Arten von Phoberomys unterschiedliche ontogenetische Stadien eines oder mehrerer Taxa innerhalb einer Gattung repräsentieren könnten.

A New Pliocene Capybara (Rodentia, Caviidae) from Northern South America (Guajira, Colombia), and its Implications for the Great American Biotic Interchange

One of the most striking components of the modern assemblage of South American mammals is the semiaquatic capybara (Caviidae, Hydrochoerinae), the biggest rodent in the world. The large hydrochoerines are recorded from the middle Miocene to the present, mainly in high latitudes of South America. Although less known, they are also recorded in low latitudes of South America, and in Central and North America. We report the first record of capybaras from the late Pliocene of Colombia, found in deposits of the Ware Formation, Guajira Peninsula in northeastern Colombia. We analyze the phylogenetic position within Caviidae, the possible environmental changes in the Guajira Peninsula, and the implications of this finding for the understanding of the Great American Biotic Interchange. The morphological and phylogenetic analyses indicate that the hydrochoerine of the Guajira Peninsula is a new species, ?Hydrochoeropsis wayuu, and this genus is most closely related to Phugatherium. According to the latest phylogenetic results, this clade is the sister group of the lineage of the recent capybaras (Neochoerus and Hydrochoerus). ?Hydrochoeropsis wayuu is the northernmost South American Pliocene hydrochoerine record and the nearest to the Panamanian bridge. The presence of this hydrochoerine, together with the fluvio-deltaic environment of the Ware Formation, suggests that during the late Pliocene, the environment that dominated the Guajira Peninsula was more humid and with permanent water bodies, in contrast with its modern desert habitats.