THE NEOTROPICAL FOSSIL RECORD AND THE GREAT AMERICAN BIOTIC INTERCHANGE

In order to get a full understanding of the evolutionary role of the Great American Biotic Interchange (GABI - land mammal exchange between North and South America following the closure of the Central American Seaway), we need to characterize the Neotropical community composition throughout GABI’s migrational intervals (i.e., pre-migration, migration, and post-migration). Unfortunately, given the scarce of knowledge from Neotropical fossil sites, current hypotheses about diversity dynamics during this migration event have been based on the paleobiological study of temperate (distal) sites. Here, we present a preliminary taxonomical report of several faunistic assemblages recently found in the Guajira Peninsula, northeastern Colombia). These faunas are of early-middle Miocene (17-15 Ma) and Latest Pliocene to early Pleistocene (~3-1.5 Ma) age. The combined mammal assemblage includes five orders (i.e., Xenarthra, Litopterna, Notoungulata, Astrapotheria and Rodentia) and ten families (i.e., Megatheridae, Nothrotheridae, Glyptodontidae, Pampatheriidae, Hydrochoeridae, Neoepiblemidae, Echymidae, Protherotheridae, Toxodontidae and Astrapotheridae), all with South American affinities. Additional fieldwork, with an increase in sampling effort will likely augment the taxonomical diversity of these sites. Due to its age and geographical location, the Guajira Peninsula is a critical window for characterizing the Neotropical mammal community through GABI’s migrational intervals. We complement field data through analyzing the composition of late Neogene mammal communities in the Americas by computing the percentage of both native and migrational faunas across a latitudinal gradient, using the Paleobiology Database (www.paleodb.org). Our preliminary results suggest that migrations started in the late Miocene (10 Ma), but most exchange occurred after the early Pliocene (~5 Ma). In tropical South America migrants are recorded only after the middle Pleistocene. Although tropical data is scarce and have to be taken carefully, a similar pattern is observed in temperate South America. While there are some records of North American migrants in this region during the Miocene and Pliocene, it is not until the Pleistocene when migrants became common, representing 75% or more of the mammal fauna.