Three-toed browsing horseAnchitherium(Equidae) from the Miocene of Panama

Abstract

During the Cenozoic, the New World tropics supported a rich biodiversity of mammals. However, because of the dense vegetative ground cover, today relatively little is known about extinct mammals from this region (MacFadden, 2006a). in an exception to this generalization, fossil vertebrates have been collected since the second half of the twentieth century from Neogene exposures along the Panama Canal. Whitmore and Stewart (1965) briefly reported on the extinct land mammals collected from the Miocene Cucaracha Formation that crops out in the Gaillard Cut along the southern reaches of the Canal. MacFadden (2006b) formally described this assemblage, referred to as the Gaillard Cut Local Fauna (L.F., e.g., Tedford et al., 2004), which consists of at least 10 species of carnivores, artiodactyls (also see recent addition of peccary in Kirby et al., 2008), perissodactyls, and as described by Slaughter (1981), rodents. Prior to the current report, the horses (Family Equidae) from the Gaillard Cut L.F. consisted of only four fragmentary specimens including: two isolated teeth, i.e., one each ofArchaeohippussp. Gidley, 1906 andAnchitherium clarenceiSimpson, 1932; a heavily worn partial dentition with p2-p4 ofA. clarenci; and a partial calcaneum ofArchaeohippus.Although meager, these fossils appear to represent two distinct taxa of three-toed horses otherwise know from the middle Miocene of North America, i.e., the dwarf-horseArchaeohippussp. and the largerAnchitherium clarencei.