E. Díaz-Martínez e I. Rábano (Eds.), 4th European Meeting on the Palaeontology and Stratigraphy of Latin America Cuadernos del Museo Geominero, nº 8. Instituto Geológico y Minero de España, Madrid, 2007. ISBN 978-84-7840-707-1 © Instituto Geológico y Minero de España THE TECTONIC SETTING OF THE CARIBBEAN REGION: KEY IN THE RADICAL LATE CRETACEOUS-EARLY PALEOCENE SOUTH AMERICAN LAND-MAMMAL TURNOVER E. Ortiz-Jaureguizar and R. Pascual Facultad de Ciencias Naturales y Museo, Paseo del Bosque s/n, B1900FWA La Plata, Argentina. [email protected], [email protected] Keywords: Mesozoic, Cenozoic, paleogeography, mammal turnover, immigration, extinction. INTRODUCTION Earlier the Caribbean Region, and later Central America, has played a crucial role in the mutual bio- geography and evolution of the North and South American faunas. Emplacement of the Panamanian isth- mian bridge some 3 Ma ago was the essential geological event that triggered the so called Great American Biotic Interchange (GABI; see Stehli and Webb, 1985). Today we know that with the exception of the caviomorph rodents and platyrrhine primates (arrived from Africa during Late Eocene-Early Oligocene) the mammals recorded in South America before the GABI (i.e., marsupials, xenarthrans, and “ungulates”) were endemic from South America but descendant of North American immigrants. They arrived from the Late Cretaceous on, during the successive stages of the Caribbean and Central American differentiation (see Pascual and Ortiz-Jaureguizar, in press, and references therein). The historical knowledge of those sup- posed oldest (Paleogene and partially Neogene) South American mammals was first reviewed by Simpson (1940, 1950, 1980 and references therein). But neither Simpson nor contemporary authors noticed that those supposedly oldest South American mammals were representing just the last third of the South American mammal history. But in 1982, Bonaparte and colleagues discovered in Patagonia the first unquestionable Late Cretaceous mammals, together with hadrosaurs dinosaurian remains, which permit- ted to have the first approximated idea of the compositional status of a South American Cretaceous land- mammal.community (see Bonaparte, 1996 and references therein). Furthermore, these discoveries (as well as other discoveries in Patagonian Early Paleocene land-mammal bearing beds (see Pascual and Ortiz- Jaureguizar, in press and references therein) led Pascual (see 2006 and references therein) to recognized that the whole history of South American mammals can be divided into two quite distinct and unrelated episodes: The Gondwanan Episode (?Late Triassic-Late Cretaceous) and The South American Episode (Early Paleocene-Recent), represented by phylogenetically unrelated actors, that respectively dwelt in likewise dis- tinct sceneries. Those mammals of the Gondwanan Episode were almost exclusively Gondwanan non- and pre-tribosphenics mammals, while those characterizing the South American Episode were just Theria, most- ly immigrants from North America with a Laurasian history. Both Episodes were separated by a critical lat- est Cretaceous-earliest Paleocene hiatus, during which South American land-mammals communities expe- 301 E. Ortiz-Jaureguizar and R. Pascual rienced a notably evolutionary change: the almost complete extinction of the Gondwanan mammals, and the arrival and radiation of the North American marsupials and placentals (see Pascual, 2006; Pascual and Ortiz-Jaureguizar, in press, and references therein). On the basis of the last paleontological and geological evidence, in this communication we analyse the compositional changes recorded in the Late Cretaceous-Paleocene South American land-mammal faunas in the context of the tectonic setting of the Caribbean Region, as one very important contributing cause of latest Cretaceous-Early Paleocene total extinction of the South American Gondwanan land-mammals. THE SOUTH AMERICAN LAND-MAMMAL FAUNAS DURING THE LATE CRETACEOS-PALEOCENE SPAN The very first steps of the history of South American mammals took origin ca.130 Ma, when the South American plate, still connected to the Antarctic Peninsula, began to drift away from the African-Indian plate. Most of the Mesozoic history of the South American mammals is still unknown, and we only have a very few and enigmatic taxa (i.e., a Jurassic Australosphenida and an Early Cretaceous Prototribosphenida) that pose more evolutionary and biogeographic questions that answers (Pascual and Ortiz-Jaureguizar, in press). The best known South American Mesozoic land-mammals were found in Late Cretaceous (Campanian-Maastrichtian) Patagonian beds. They are represented by several non- and pre-tribosphenic endemic genera (one “plagiaulacidan” multituberculate, two gondwanatherians, one docodont, one “tri- conodont”, one “symmetrodont” and ten dryolestoids), that are relict of pangeic lineages, which were extinct in coeval beds of Laurasia (see Kielan-Jaworowska et al., 2004; Pascual and Ortiz Jaureguizar, in press). The total absence of tribosphenic mammals in Patagonian Late Cretaceous beds (well diversified in coeval Laurasian beds), and the advanced morphology and endemism of non-tribosphenic and pre-tri- bosphenic ones was interpreted as an evidence of the long isolation of South America from the North American continent (see Bonaparte, 1996; Kielan-Jaworowska et al., 2004; Pascual, 2006; Pascual and Ortiz-Jaureguizar, in press). But the so recently finding of a new genus and species of a ?cimolodontan multituberculate, the first found in those Late Cretaceous Patagonian beds (Kielan-Jaworowska et al., 2007) could change, at least in part, the classic scenario of a completely isolated South American land- mammal fauna. According to Kielan-Jaworowska et al. (2007), the new multituberculate is a North American immi- grant that could be arrived to South America during Early Cretaceous or Late Cretaceous. The hypothesis of an Early Cretaceous arrival is supported by the presence of some morphological features that are shared with “Plagiaulacida”, a multituberculate suborder which did not cross the Early-Cretaceous-Late Cretaceous boundary. But there is not fossil evidence among the South American vertebrates of an arrival of North American immigrants during Early Cretaceous. Additionally, to us this is not the only cimolodon- tan multituberculate that shows a mosaic of plagiaulacidan (plesiomorphic) and cimolodontan (apomor- phic) characters. The “Paracimexomys group” (i.e., the most plesiomorphic, informal group of Cimolodonta) share some molar features with some “Plagiulacida” (i.e., Plagiaulacidae and Eobaataridae). They were recorded in Early Cretaceous (Aptian/Albian) to Late Cretaceous (Maastrichtian) beds of North America, as well as in Late Cretaceous (?Maastrichtian) ones of Europe. (Kielan-Jaworowska et al., 2004). Consequently, we can also suppose that the new Patagonian taxon was a South American representative of a clade of basal cimolodontans (not yet recorded in the “classical” Late Cretaceous North American 302 THE TECTONIC SETTING OF THE CARIBBEAN REGION: KEY IN THE RADICAL LATE CRETACEOUS-EARLY PALEOCENE SOUTH AMERICAN LAND-MAMMAL TURNOVER Figure 1. Cretaceous paleogeographic reconstruction of Caribbean region, mdified from Iturralde-Vinent (2004) and Iturralde- Vinent and McPhee (2004). A, Early Cretaceous (125-120 Ma); B, Late Cretaceous (ca. 70 Ma). References: Black areas: emerged lands; Grey areas: shallow sea; White areas: deep sea; White squares: volcanoes. mammal-bearing beds) that arrived to South America during Late Cretaceous. Additionally, all the paleo- geographic reconstructions of the Caribbean-“Central America” area (Fig. 1 and see below) favor a Late Cretaceous inter-American vetebrate exchange. The Late Cretaceous migratory events suggest that there was some kind of inter-American dry land connection by the end of the Cretaceous, which for sure was transitory (geologically speaking) and throughout the incipient Caribbean Sea. THE GEOLOGIC AND TECTONIC SETTING OF THE CARIBBEAN REGION The creation of the Caribbean Plate was probably the most important aspect of a timing sequence for a link between the North and South America land masses (Smith, 1985). The general geologic and tectonic setting of the Caribbean region is crucial to evaluating the very first recorded interchange of land verte- brates between North and South America during the Late Cretaceous. As Case et al. (2004) stated regard- ing the marsupials, and the contribution to an appraisal of mammalian dispersal of other groups of land vertebrates (e.g., the dispersal history of hadrosaurine dinosaurs and booid snakes; see Estes and Báez, 1985; Gayet et al., 1992), the window of dispersal seems to begin in the Campanian, to be most likely in the Maastrichtian, and to wane in the Paleocene. These authors, essentially based on the fossil evidence afforded by fossil marsupials, concluded that “…the dispersal probability is best proposed as having been a sweepstakes to a relatively strong filter”, as Simpson (1953) proposed. To them, the Aves Ridge could have provided the dried dispersal route for land vertebrates between North and South America during the Campanian-Maastrichtian span. On the contrary, Iturralde-Vinent and Mac Phee (1999, 2004) concluded that no permanent landmasses were present in the Caribbean prior to the middle Eocene. However, to these authors the NW margin of the Caribbean Plate was the area where emerged volcanic islands were aligned between North and South America