New Notoungulates (Notostylopidae and Basal Toxodontians) from the Early Oligocene Tinguiririca Fauna of the Andean Main Range, Central Chile

Here we describe two new notoungulate taxa from early Oligocene deposits of the Abanico Formation in the eastern Tinguiririca valley of the Andes of central Chile, including a notostylopid (gen. et sp. nov.) and three basal toxodontians, cf. Homalodotheriidae, one of which is formally named a new species. The valley's eponymous fossil mammal fauna became the basis for recognizing a new South American Land Mammal "Age" intervening between the Mustersan and Deseadan of the classical SALMA sequence, the Tinguirirican. As a temporal intermediate between the bracketing SALMAs (Deseadan and Mustersan), the Tinguirirican is characterized by a unique cooccurrence of taxa otherwise known either from demonstrably younger or more ancient deposits, as well as some taxa with temporal ranges restricted to this SALMA. In this regard, two of the notoungulates described here make their last known stratigraphic appearances in the Tinguiririca Fauna, Chilestylops davidsoni (gen. et sp. nov.), the youngest notostylopid known, and Periphragnis vicentei (sp. nov.), an early diverging toxodontian, the youngest representative of the genus. A second species of Periphragnis from the Tinguiririca valley is provisionally described as Periphragnis, sp. nov., but is not formally named due to its currently poor representation. A specimen referred to Trigonolophodon sp. cf. T. elegans also is described. This taxon is noteworthy for also being reported from Santiago Roth's long perplexing fauna from Canadon Blanco, now considered Tinguirirican in age. A phylogenetic analysis of notostylopids identifies Chilestylops as closely related to Boreastylops lumbrerensis from northern Argentina.