Two new notoungulates (Family Notohippidae) from the Salla Beds of Bolivia (Deseadan: late Oligocene): systematics and functional morphology

Three notohippids from the Salla Beds of Bolivia (Deseadan, late Oligocene) are described: Pascualihippus boliviensis, gen. et sp. nov., Eurygenium pacegnum, sp. nov., and Rhynchippus sp., cf. R. brasiliensis. P. boliviensis has a transverse premaxillary dental arcade similar to that of toxodontids, suggesting a close relationship to the origins of Toxodontidae. E. pacegnum is represented by a virtually complete articulated skeleton, having a tetradactyl manus and proximal third trochanter, whereas Rhynchippus equinus and early toxodontids share the derived conditions of tridactyl manus and more distally placed third trochanter. Phylogenetic analysis suggests that toxodontids are nested within the paraphyletic Notohippidae. A recent, more inclusive concept of notohippids may also include Leontiniidae. The relative height of tooth crowns and relative width of muzzles were used to infer the feeding ecologies of Salla notohippids. Based on its broad muzzle, Pascualihippus is hypothesized as being principally a grazer, whereas the narrow muzzle of E. pacegnum and R. sp., cf. R. brasiliensis could have enabled them to select specific nutrient-rich food items, such as budding leaves. These latter two species are inferred to have been mixed feeders because their hypsodont dentition would have also permitted them to tolerate abrasives in food items, such as grasses.