New fossil primate from Chile.

Abstract

The southern parts of South America have yielded an important collection of a growing number of fossil platyrrhines, but the records so far have come exclusively from the Argentine Patagonia. No fossil primates have been found previously in southern Chile until the discovery of an isolated talus described below. This specimen was collected in February, 2000, at the locality of Alto Rio Cisnes, Aisen, Chile (Fig. 1), during a paleontological expedition of the Facultad de Ciencias Naturales, Sede Esquel (Universidad Nacional de la Patagonia “San Juan Bosco”). It is the second fossil primate ever found in Chile, after Chilecebus from the central part of the country (Flynn et al., 1995). The new talus (Fig. 2; Table 1) was collected at locality 5 of Marshall and Salinas (1990). It is approximately the size of Pithecia or slightly smaller and similar to other fossil tali found in Patagonia, such as that of cf. Dolichocebus from Gaiman (Gebo and Simons, 1987), those of cf. Soriacebus and cf. Carlocebus from Pinturas (Meldrum, 1990), and the recently described specimen from Canadon del Tordillo attributed to Proteropithecia (Kay et al., 1998). The new specimen SGO-PV 974 shows the following morphological characters. The talar head is broken dorsally, but appears oval in distal view. The talar neck is long relative to the body, forming an angle of about 45( relative to the plane of the fibular facet of the trochlea. In plantar view, the transition between the navicular facet and the anterior calcaneal facet is smooth with no ridge. The trochlea is moderately high, almost parallelsided and fairly flat, with a shallow trochlear groove. Also, the dorsal surface of the trochlea extends onto the dorsal surface of the neck, where a distinct lateral tibial stop is present. The medial tibial malleolar surface ends distally in a relatively shallow depression. The pit for the posterior talofibular ligament is deep. The lateral trochlear rim is sharp, but the distal end does not project forward, while the medial trochlear rim is lower and more rounded. The fibular trochlear facet is nearly flat, but the lateral process is broken. Both the posterior medial and lateral tubercles are eroded. The posterior calcaneal facet is long and quite broad and extends onto the posterior medial tubercle. Functionally, the characters described above indicate that the Rio Cisnes talus was from a predominantly quadrupedal and arboreal platyrrhine, with some features associated with leaping behavior (i.e., moderately high talar body with parallel-sided rims and long neck; see Gebo and Simons, 1987; Meldrum, 1990, 1993). Concerning this morphology, Meldrum (1990) has also found similarities between the tali of Carlocebus (which is the most similar to the Rio Cisnes talus—see below) and callitrichines, reflecting generalized quadrupedal adaptations, but lacking E-mail address: mtejedor@ciudad.com.ar (M.F. Tejedor). ARTICLE IN PRESS