The Eocene SANUs from the Chubut River Valley (Cerro Pan de Azúcar and Bryn Gwyn, Chubut, Argentina)

Abstract

As result of the expedition during 1897 in the Valle Inferior del Río Chubut, near Gaiman city (Chubut Province, Argentina), the Swiss naturalist Santiago Roth collected a small but interesting assemblage of South American native ungulates from the Paleogene fossiliferous levels of the Cerro Pan de Azúcar fossil locality. Here, after more than one hundred years after, most of them are first figured and described. We propose a different taxonomic interpretation for Monolophodon minutus and Lelfunia haugi, the two ungulate species endemic for this locality. We also describe the specimens of other historical collections from both Cerro Pan de Azúcar and Bryn Gwyn fossil sites gathered by several expeditions throughout the 20th century. We recognize two clearly distinguished assemblages of South American Native Ungulates. The presence of Henricosbornia lophodonta, Kibenikhoria sp., Isotemnus sp., Notoungulata indet., and Peripantostylops sp. in the upper Las Flores Formation at Cerro Pan de Azúcar establishes affinities with other faunas from the same unit (Cañadón Hondo and Bajo Palangana, Chubut Province) and suggests a slightly older age than the Vacan fauna. On the other hand, the presence of Oldfieldthomasia sp., Henricosbornia lophodonta, Notostylops sp., and Trigonostylops sp. in the Pan de Azúcar Member (lower Sarmiento Formation) at Pan de Azúcar fossil site and Thomashuxleya sp. in Bryn Gwyn fossil site establishes affinities with the Barrancan faunas of the Sarmiento Formation, suggesting a Bartonian age for these levels.