UC Santa Barbara

Two new Oligocene “notohippids” from the Abanico Formation, a geographically widespread volcanic and volcaniclastic lithostratigraphic unit in the Andean Main Range of central Chile, are described and subjected to phylogenetic analysis. “Notohippidae” is a paraphyletic assemblage of medium-sized South American native ungulates from the Casamayoran (middle Eocene) to Santacrucian (early Miocene) SALMAs (South American Land Mammal Age). This group belongs to Notoungulata, the most diverse clade of native South American ungulates.

The two new taxa are represented by SGOPV 3750, consisting of a cranium and partial upper dentition recovered near Upeo, Chile (~200 km south of Santiago), which represents a new genus, and SGOPV 3221, a nearly complete upper dentition collected from the Las Leñas drainage basin (100 km SSE of Santiago), representing a new species of Rhynchippus. Specimens from the Salla Beds, Bolivia, originally assigned to Rhynchippus brasiliensis are here referred to the same new species of Rhynchippus as proposed for SGOPV 3221. A phylogenetic analysis resolves a sister group relationship between Eurygenium and Argyrohippus for the first time, but “Notohippidae” remains paraphyletic. The taxa described here nest within a polytomy including the pairing of Eurygenium and Argyrohippus, Rhynchippus equinus, R. pumilus, and a clade comprising Pascualihippus boliviensis plus Toxodontidae.