New fossil mammals from the northern neotropics (Urumaco, Venezuela; Castilletes, Colombia) and their significance for the latitudinal gradient in diversity and the Great American Biotic Interchange.

SÁNCHEZ-VILLAGRA M.; CARRILLO, J.; CARLINI A.A.; JARAMILLO, C.

Berlin

Congreso; 74th Meeting Berlin, SVP, Society of Vertebrate Paleontology; 2014

SVP

The Great American Biotic Interchange (GABI) refers to the faunal exchangebetween North and South America around the time of closure of the Central AmericanSeaway, an event that modified the mammal fauna of both continents. Current hypothesesabout diversity dynamics during this event have been mostly based on data fromtemperate sites. We present new data from the Urumaco sequence in Venezuela and fromnew sites at the Guajira Peninsula, northeastern Colombia, which together comprise aseries of faunas from the early Miocene to the early Pliocene. Due to their age andgeographical location, they serve to characterize the Neotropical mammal communitybefore and after GABI′s migrational intervals. Studies of taxonomic groups involve teamsof researchers. In Urumaco the greatest diversity of mammals is in the xenarthrans, withat least 20 species of Mylodontids, Megalonychids, Megatherines, Glyptodontids,Pampatherids, and Dasypodids. Some species provide insights into the re-ingression fromNorth America, taxonomic affinities with megalonychids otherwise present in theCaribbean islands, and the record in these northern latitudes of ?basal? forms recorded inearlier deposits of higher latitudes. Among rodents, the revision of both new dental andpostcranial remains and their variation revealed that several species must have existed,including Phoberomys pattersoni, Eumegamys sp., and Neoepiblema sp. Among the″meridiungulata″, cranial remains of toxodonts suggest the presence of forms withplesiomorphic features unexpected for animals at this geological age. Astrapotheresinclude cranial remains from Castilletes representing the oldest record ofUruguaytheriinae in the tropics, whereas materials from the Urumaco sequence arepostcranials which provide insights into locomotory style. The oldest procyonidcarnivores from the northern neotropics are recorded based on dental remains, fromCastilletes and Urumaco (San Gregorio Fm.). We complement field data by compilingand analyzing the composition of late Neogene mammal assemblages in the Americas bycomputing the percentage of both native and migrational faunas across a latitudinalgradient. Migrations started in the late Miocene (~10 Ma), but most exchange occurredafter the early Pliocene (~5 Ma). In tropical South America migrants are first recorded inthe Pliocene. In temperate South America, there are records of North American migrantsduring the late Miocene and Pliocene, but it is not until the Pleistocene when migrantsbecame common