Urumaco and Venezuelan Paleontology: The Fossil Record of the Northern Neotropics

13 The South American Native Ungulates of the Urumaco Formation

256 The South American Native Ungulates of the Urumaco Formation Mariano Bond and Javier N. Gelfo The mammalian fauna of Cenozoic South America is known from the scientific literature to be mainly composed of a series of different aggregate waves of migrants, which originally were recognized and characterized by Simpson (1950) as the first to the third “strata.” The living mammal fauna of South America still retains members of the three “strata,” but during the Cenozoic the orders of endemic ungulates pertaining to the first stratum became extinct. The living South American ungulates are all northern immigrants from the third stratum. The zenith of the South American endemic or native ungulates can be traced back to the Paleogene. In the Casamayoran South American Land Mammal Age (SALMA) (Eocene) they are represented, conservatively, by five “orders” and more than forty genera. During later times in the Cenozoic there was a significant diminution in the taxonomic diversity, though a reduction in abundance of specimens has not been observed. This was a consequence of worldwide environmental changes that affected the biota during the Eocene and Oligocene transitions. During these transitions the decrease of worldwide temperature (Zachos et al. 2001, 2003) led to the modern “Icehouse-World.” As a consequence mammalian communities underwent several changes in their lineages. This global climatic change led to several faunal changes, such as the “Grande Coupure” in Europe. In South America the end of the Eocene was associated with several geological events. Among them, sea-level fluctuation and the rise of the Andes mountain range accentuated climatic changes in South America. So during the Early Neogene (fig. 13.1), for example in the Santacruzian SALMA (Early Miocene), endemic ungulates were reduced from five to three orders (Astrapotheria, Litopterna, and Notoungulata) and nearly 50% of the genera, and holdover lineages became specialized and distinctive , almost “stereotyped” within each group. The evolutionary history of the native ungulates, as well as that of many other South American mammals, is based mainly on the Cenozoic fossil record from Argentina, with a considerable latitudinal range of fossiliferous sites. Hence this history is biased, when we consider all of South America, especially due to the scattered and sometimes scarce fossil record of the more tropical areas. In these outcrops scientific research has been not so extensive as it has been in Argentina, in part due to dif13 The South American Native Ungulates of the Urumaco Formation 257 Fig. 13.1. Standard chronostratigraphy and SALMAs for the Neogene. Modified from TSCreator PRO (Version 1.3; 2008) James Ogg (database coordinator ) and Adam Lugowski (software developer), www. tscreator.com. Bond and Gelfo 258 ficulties in the field (rare preservation and limited access to outcrops; e.g., large fluvial basins subjected to extensive inundation). Considering the Venezuelan fossil record, the oldest mammal is supposed to come from Eocene rocks of Trujillo state. It was described by Patterson (1977) as Proticia venezuelensis and interpreted as a representative of the Pyrotheria, a bilophodont order of South American native ungulates. But its stratigraphic provenance and phylogenetic affinities were questioned by Sánchez-Villagra et al. (2000). Proticia venezuelensis is represented by a jaw fragment with p3-m1. The fossil was collected in 1964 by a second person, several years before Patterson visited the supposed locality in 1970. As related by Patterson (1977), the fossil was reported to be found in a spot along the Quebrada de Agua Viva, which is located about 13 km west of the Cerro La Cruz locality. As described by Sánchez-Villagra et al. (2000), in 1995 Rich Kay, Roberto Lozsan, Rick Madden, and Marcelo R. Sánchez-Villagra visited the purported collection spot of Proticia venezuelensis (Patterson 1977), with the help of Don Guillermo, a local resident who accompanied Patterson in 1970 to the locality. They found no traces of any vertebrate fossil in the area and, based on this observation (also experienced by Patterson 1977, 400), suggested that the provenance of P. venezuelensis should be put into question . P. venezuelensis is more likely to have come from the rocks of the Castillo Formation. Its dental anatomy places the phylogenetic position of this taxon in question. A cuspate tooth form (lack of bilophodonty) and the presence of thick enamel make the possibility of sirenian affinities worth testing (Sánchez-Villagra et al. 2000). This would correspond well with the kind of environment in which Sánchez-Villagra et al. (2000) suggested this...