Dental microwear in Triassic amniotes: implications for paleoecology and masticatory mechanics

Abstract

ABSTRACT Features of dental microwear have been used to infer diet in fossil mammals based on comparisons with analogues or modern representatives, because material properties of the food and jaw mechanics can be inferred from microwear attributes that are easily compared across diverse groups. However, only rarely has dental microwear analysis been applied to more ancient non-mammalian taxa without modern relatives. We examine patterns of dental microwear in two distantly related groups-traversodontid cynodonts (at least two distinct taxa) and a possible ‘prosauropod’ dinosaur, both from the mid-late Triassic of Madagascar. Pitting was absent in most specimens examined. Scratch length and orientation heterogeneity, factors that have been suggested to reflect the hardness of the diet, differ significantly between the traversodontids and the ‘prosauropod’ analyzed, and may suggest some degree of resource partitioning between these two types of coexisting herbivores. The ‘prosauropod’ appears to have fed on softer plant material than the traversodontids did, whereas shorter scratch lengths and lower orientation consistency suggest that the traversodontids fed on more resistant vegetation. Rose diagrams of orientations of microwear features exhibit a clear bimodality of jaw motion in the traversodontid cynodonts, with a dominant postero-dorsal power stroke and significant horizontal motion in the antero-posterior direction. In contrast, the ‘prosauropod’ jaw motion was simple and orthal.