New insights on the Kibenikhoria and Ernestokokenia faunas and the implications for the early Eocene of Patagonia, Argentina

Abstract

The Kibenikhoria and Ernestokokenia local faunas were described in the 1930s by George G. Simpson, who defined them as two chronologically consecutive faunas based on a comparison with the Casamayoran South American Land Mammal Age (SALMA). Later, in the 1980s, the two faunas were respectively the basis of the Itaboraian and Riochican SALMAs, a scheme broadly accepted for more than eight decades. However, a systematic revision of their native ungulates is still lacking. In this contribution, we studied several collections performed in the classical localities of Cañadón Hondo and Bajo Palangana (southeastern South America) and discuss the systematic status of the mammals listed in their faunas. Our results allow us to (1) assert that the beds containing the mammal associations in Cañadón Hondo and Bajo Palangana are located in the upper Las Flores Formation and are essentially contemporaneous; (2) improve the knowledge for Kibenikhoria get and Henricosbornia lophodonta; (3) propose H. waitehor and ?Peripantostylops orehor to be synonymous with H. lophodonta; and (4) recognize Shecenia ctirneru, Seudenius cteronc, and ?Postpithecus as Trigonostylopidae aff. Trigonostylops. The Kibenikhoria and Ernestokokenia faunas have six genera in common; five of them are shared with the lower levels of the Sarmiento Formation. Kibenikhoria get, Isotemnus ctalego, Pliodolops winecage, and Gasternia ctalehor are exclusive taxa of the Kibenikhoria fauna. Here, the Riochican sensu stricto from Marshall is used to include both local faunas, which represents a distinct and more derived fauna than that from theItaboraí Formation, but with a less advanced evolutionary stage than the lower Sarmiento Formation.