New evidence of the sabertooth cat Smilodon ( Carnivora : Machairodontinae ) in the late Pleistocene of southern Chilean Patagonia Nueva evidencia del gato dientes de sable Smilodon ( Carnivora : Machairodontinae ) en el Pleistoceno tardío de Patagonia meridional chilena

Southern Patagonia is rich in late Pleistocene mammals, especially herbivores such as Camelids, Equids and Xenarthrans. Carnivores, on the other hand, are not commonly found in the paleontological record. One genus, Smilodon, is of particular interest because its presence in the region has not been demonstrated. In this paper, we present new fossil dental evidence that supports the presence of Smilodon populator (Lund) in the region. This evidence corresponds to the most southern record of the genus in the world, and the final step in the colonization of South America after the Great American Biotic Interchange. An AMS radiocarbon date on teeth indicates that the remains from Southern Chilean Patagonia are the most recent record for the genus in South America.

This work discusses the presence of Smilodon, and particularly, S. populator during the late Pleistocene in the Chilean Patagonia, starting from fossils found in two well-known caves from the area, Cueva Lago Sofía 4 and Cueva del Medio.

METHODS
For the morphological analysis, the remains were compared with (1) modern dental pieces of Puma concolor (Linnaeus, 1758) stored at Centro de Estudios del Hombre Austral, Universidad de Magallanes (CEHA), Punta Arenas, Chile; (2) fossil material from Smilodon populator stored at Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Buenos Aires, Argentina (MACN) and Museo de La Plata (MLP), La Plata, Argentina; and (3) a resin replica of Smilodon fatalis from Rancho La Brea stored at CEHA.Osteological terminology from Merriam and Stock (1932) was used for the description.In order to compare the size of the Smilodon specimens from Southern Chile with those found in other parts of America, we conducted an analysis of logarithmic distances 1 , using metrical data from Merriam & Stock (1932), Berta (1985Berta ( , 1987)), Kurtén & Werdelin (1990), as well as personal data gathered at MLP and MACN, and unpublished data from F. Prevosti (personal communication, 2008) (Appendix A and B).Meausurements are in milimeters with 0.1 mm accuracy.
The specimens under study are housed at the Centro de Estudios del Hombre Austral, Universidad de Magallanes (CEHA) in Punta Arenas, Chile.

Description and comparison
The piece UMAG 86661(i-08) corresponds to a proximal portion of a large left-upper canine.According to Berta (1985Berta ( , 1987)), the upper canine from Smilodon genus has unusual growth, lateral compression, acuminate morphology, curved towards its distal end and fine serrations on the edges.The piece from Lago Sofía 4, although it was fractured, has dimensions matching Smilodon (Appendix A) with a laterally compressed cross-section and a slight curvature.The specimen is only a root, so there is no distal serration.Despite the fact that it is incomplete, it is possible to obtain the maximum mesiodistal length (L) and maximum buccolingual width (W) (Appendix A).Berta (1985) as well as Kurtén and Werdelin (1990) state that S. populator, particularly the Lujanian form is the largest species within the genus.Berta (1985Berta ( , 1987)), nevertheless, mentions that a classification based exclusively on size is not reliable because of sexual dimorphism and/or typical variations of animals with wide geographical distribution (i.e., "Bergmann's rule").Kurtén and Werdelin (1990), however, have demonstrated that although there was some degree of sexual dimorphism in Smilodon, this was less than in other widespread felids (e.g., Puma concolor).The analysis of logarithmic distances using the canine bucolingual maximum width and taking MLP-83-I-15-3 as reference (Appendix A) indicates that the CLS-4 tooth has a size compatible only with S. populator (Fig. 3A).

Description and comparison
The piece UMAG 29/12bN408 is a large rightupper third incisor.It has a great development of the main cusp, an oval section, a slight compression in its lateral section, and is curved towards its distal end.Its medial side has a groove that runs from the tip of the crown to its base.The enamel on its lateral side is fractured.Both sides of the lingual section show two slightly flattened posterior tubercles separated by a "U" shaped notch.It is worn on its occlusal surface.The big size of this tooth (Appendix B), the presence of a prominent root and posterior tubercles are features of Smilodon (Merriam & Stock 1932).The logarithmic distances using the third incisor bucolingual maximum width (W) taking the MLP 10-2 specimen as reference (Appendix B) shows that the UMAG 29/ 12bN408 tooth has dimensions similar to the largest specimens of S. fatalis from the Rancholabrean of North America and S. populator of Lujanian of South America (Fig. 3B, Appendix B), suggesting that this tooth does not have a specific taxonomic value.However, it is assigned to Smilodon cf S. populator due to its morphological and size features, chronological contemporaneity, geographical proximity and faunal composition between CDM and CLS-4.The fact that S. fatalis and S. populator have an allopatric distribution in South America supports this assignation (Kurtén & Werdelin 1990).UMAG 86433 and UMAG 46388 correspond to left and right fourth premolar fragments, respectively.Both are fractured in a very similar way, retaining the upper portion of the crown.The specimen UMAG 86433 has an almost complete metacone with a small lingual portion of the paracone.It also has a fragment of the principal root, and shows intensive occlusal wear exposing the dentine.The specimen UMAG 46388 also retains the distal section of the crown conserving a large mesial portion of the metacone and the distal portion of the paracone.The deep depression that divides both sections is complete.It has a very advanced occlusal wear on the lingual side.The similarities in occlusal wear and general size between both premolars, suggests that they probably came from the same individual.Due to the fragmentary nature of the specimens, it is impossible to obtain reliable measurements, however, the very prominent metacone and a marked depression between the metacone and the paracone are distinctive features of the genus Smilodon (Merriam & Stock 1932).Due to extensive fragmentation, UMAG 46388 and UMAG 86433 cannot be specifically assigned, however their stratigraphic relationship with UMAG-86661(i-08) permits their inclusion with the other Simlodon cf. S. populator material.

DISCUSSION
Remains of Smilodon populator have been documented in Venezuela, Brazil, Paraguay, Uruguay, Argentina, Bolivia and Chile (Berta & Marshal 1978, Berta 1985, Kurtén & Werdelin 1990, Ubilla et al. 2004, Rincón 2006).Not counting the Patagonian findings, the southernmost record of Smilodon comes from the late-Pleistocene (Lujanian-Platean) in Central Argentina (Soibelzon & Prevosti 2007).The radiocarbon date of the Smilodon tooth from Cueva del Medio corresponds to the most recent record of this taxon in South America and the southernmost occurence.The date is slightly younger than those obtained from Cueva del Milodon (Table 1).
The paleoclimatological data of the area shows that when the now extinct megafauna was alive, the climate was very cold and the landscape vegetation was more open (Heusser 1995, Cárdenas 2006, Villa-Martínez & Moreno 2007).This agrees with the faunal assemblages identified in CLS-4 and CDM, since Smilodon populator remains were found along with remains of the common grazers of open landscapes such as Mylodon darwini, Hippidion saldiasi (Roth, 1899), Lama guanicoe (Müller, 1776) and Vicugna vicugna (Nami & Mengaz 1991, Borrero et al. 1997).During the late Pleistocene, Smilodon populator was at the top of the foodweb.Prevosti & Vizcaíno (2006) suggest that S. populator could have captured an animal of 1,871 kg.For this reason, all the Pleistocene mammals recorded in southern Patagonia were potentially prey.In this scenario, S. populator competed against other large carnivores, such as Arctotherium tarijense (Ameghino 1902) and Panthera onca mesembrina.The morphology of the limbs suggests that Smilodon was not able to run long distances and accelerate quickly, thus, its hunting strategy most likely focused on ambush instead of pursuit in relatively closed environments (Gonyea 1976, Turner & Antón 1997).Given the large areas of open landscape in southern Patagonia, S. populator may have complemented its hunting strategy by incorporating pursuit at least occasionally.The presence of this sabertooth at the very tip of South America demonstrates the high adaptability of the species.