Inter- and intraspecific variation in theropod dinosaur dental microwear and its palaeoecological implications

Differences in skull and tooth morphology, stomach contents, and estimated bite force between medium-to-large sized (≥100 kg) predatory theropod dinosaurs have long been suspected to correlate with differences in their diets and dietary guilds (e.g., hypercarnivory, piscivory). However, excluding exceptionally rare specimens with associated stomach contents or coprolites, the diets and dietary guilds of these taxa can be difficult to infer in detail. To enable comparisons across a wider array of taxa, especially those lacking stomach contents, an accurate, reliable proxy for diet needs to be employed. Dental microwear texture analysis (DMTA) has been used to investigate the diets of extant and extinct diapsids through examination of micron-scale surface textures. Here, we present a pilot study to determine the utility of DMTA for assessing diet in theropod dinosaurs and whether single teeth can act as a proxy for microwear across the entire dentition. To accomplish this, we examined texture variation along the tooth row in four medium-to-large-bodied theropods: Allosaurus, Ceratosaurus, Irritator, and Tyrannosaurus. Our results suggest that tooth position does affect DMTA and therefore DMT samples should be constrained using the following three guidelines: teeth should be sampled from within a single cranial element (premaxilla, maxilla or dentary); if comparing across elements, samples should be constrained to a single side of the teeth (labial or lingual); and comparisons across the labial surfaces of the dentary and maxillary teeth should be avoided. Our findings imply that taxonomically distinct isolated theropod teeth can be used to infer the dietary ecology of theropod faunal assemblages if constrained sampling occurs.