FOSSIL TURTLES FROM THE TROPICS

Since their first appearance in the late Triassic turtles have been one of the most successful groups of reptiles, surviving mass extinction events, showing high diversity, high morphological variation in their shell and skull, and remarkable adaptability to terrestrial as well as freshwater and marine environments from the tropics to high latitudes on all continents. Early in their history, turtles split into two major groups known as Cryptodires, or hidden-necked turtles, and Pleurodires, or side-necked turtles, with additionally differences in their skulls and shells (Gaffney, et al., 2006). Pleurodires are restricted today to freshwater environments of South America, Africa, Madagascar, and Australia. Cryptodires live on land, and in freshwater and marine environments on almost all continents (Boni et al., 2006).

The fossil record particularly of pleurodires illustrates that they were a highly diverse and widespread group especially during the late Cretaceous and Paleogene, inhabiting brackish and near coastal environments (Gaffney et al., 2006). Despite many recent discoveries of fossil pleurodires (Lapparent de Broin, 2000; Gaffney et al., 2001a, 2001b; Gaffney and Wood 2002; Gaffney et al., 2002; Carvalho et al., 2002; de la Fuente, 2003; Gaffney et al; 2003; Gaffney and Tong, 2003; Gaffney and Foster, 2003; Cadena and Gaffney, 2005; França and Langer, 2005, 2006; Boquectin and Melo, 2006; Sanchez-Villagra and Winkler, 2006; Gaffney et al., 2006; Romano and Azevedo, 2006; Gaffney et al., 2007; Lapparent de Broin et al., 2007; Joyce, 2007; Sterli, 2008) a huge gap in their fossil record particularly for the tropical part of South America still exists between the Valanginian and the Miocene. Thus, there are many outstanding questions surrounding when and in what paleoenvironmental, paleobiogeographic, paleoclimatic and paleoecologic context the modern South American pleurodires originated. These questions can only be addressed with further discovery and description of turtle fossils from tropical South America.

Recently, a team composed of members from the Florida Museum of Natural History, Smithsonian Institution, Smithsonian Tropical Research Institute and some Colombian institutions discovered three new fossiliferous localities of Paleocene and Eocene age in the Northwestern part of South America, in the Eastern Cordillera (Nemocon and Mochuelo creek localities) and Guajira Peninsula (Cerrejón Coal Mine) of Colombia. The Cerrejon and Nemocon localities are middle to late Paleocene in age, base on palynological zonation (Jaramillo et al, 2007) and have shown be highly productive for fossil plants,reptiles and fishes (Herrera et al. 2005; Bloch et al., 2005; Jaramillo and Cadena, 2006; Jaramillo et al. 2007). A third locality is called Mochuelo Creek locality, recently dated as early Eocene in age, using Ar/Ar (Jaramillo 2008 pers com), this locality is recognized by fossil mammals, reptiles and fishes. Most of the fossils collected in these three localities are being prepared and studied by staff and graduated students at the Florida Museum of Natural History-University of Florida. Following complete study, the collections will be returned to local museums and natural science institutions in Colombia. Complete cast collections will also be housed at the Florida Museum of Natural History.

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