Environmental and ecological context for hypsodonty in the early Oligocene Tinguiririca Fauna, central Chile

Abstract The early Oligocene Tinguiririca Fauna from the Abanico Formation, central Chile, is the earliest mammal fauna dominated by high-crowned (hypsodont) herbivores known globally. The drivers of early hypsodonty in South America are thus of considerable interest. We reconstruct the palaeoenvironment for Tinguiririca based on: (1) generalised linear latent variable models (GLLVMs), which compare body mass distributions of Tinguirirican and modern South American herbivores; and (2) reconstructed diets of Tinguiririca fauna notoungulates inferred from dental mesowear. Based on GLLVMs, the Tinguiririca Fauna’s palaeoenvironment is interpreted as relatively warm (22˚C mean annual temperature), dry (1200 mm yr -1 mean annual precipitation) and open (23% tree cover). The Brazilian Caatinga is the closest modern South American analogue to the dry, low-vegetation-density palaeoenvironment inferred for Tinguiririca. We interpret the fauna’s notoungulates as browsers, based on their sharp ectoloph wear facets. To test this interpretation, we also analysed the mesowear angles and relative crown heights of a broad array of leontiniid and homalodotheriid notoungulates, two clades specialised for high browsing that never attained the levels of hypsodonty seen in other notoungulates. Both have sharp mesowear and greater relative crown heights than modern high browsers. Our data suggest that neither gradual habitat change nor increased levels of volcaniclastic sedimentation alone caused the early attainment of hypsodonty in notoungulates. Alternative explanations, such as one or more rapid pulses of environmental change driving the increase in hypsodonty or the unique taxonomic composition of South American faunas, must be invoked to explain the marked increase in crown height from preceding time periods into the Tinguirirican South American Land Mammal Age.