Macroevolutionary trends in theropod dinosaur feeding mechanics

Theropod dinosaurs underwent some of the most remarkable dietary changes in vertebrate evolutionary history, shifting from ancestral carnivory(1-3) to hypercarnivory(4,5) and omnivory/herbivory,(6-9) with some taxa eventually reverting to carnivory.(10-12) The mandible is an important tool for food acquisition in vertebrates and reflects adaptations to feeding modes and diets.(13,14) The morphofunctional modifications accompanying the dietary changes in theropod dinosaurs are not well understood because most of the previous studies focused solely on the cranium and/or were phylogenetically limited in scope,(12,15-21) while studies that include multiple clades are usually based on linear measurements and/or discrete osteological characters.(8,22) Given the potential relationship between macroevolutionary change and ontogenetic pattern,(23) we explore whether functional morphological patterns observed in theropod mandibular evolution show similarities to the ontogenetic trajectory. Here, we use finite element analysis to study the mandibles of non-avialan coelurosaurian theropods and demonstrate how feeding mechanics vary between dietary groups and major clades. We reveal an overall reduction in feeding-induced stresses along all theropod lineages through time. This is facilitated by a post-dentary expansion and the development of a downturned dentary in herbivores and an upturned dentary in carnivores likely via the curved bone effect.We also observed the same reduction in feeding-induced stress in an ontogenetic series of jaws of the tyrannosaurids Tarbosaurus and Tyrannosaurus , which is best attributed to bone functional adaptation. This suggests that this common tendency for structural strengthening of the theropod mandible through time, irrespective of diet, is linked to functional peramorphosisof bone functional adaptations acquired during ontogeny.

Automated summary

Theropod dinosaurs underwent significant changes in their mandibular evolution and morphological adaptations, which reflected their dietary shifts. Using finite element analysis, we found variations in feeding mechanics among different dietary groups and major clades of non-avialan coelurosaurian theropods. Overall, there was a reduction in feeding-induced stresses along all theropod lineages through time. This reduction was associated with the expansion and development of the mandible in herbivores and carnivores, likely through the curved bone effect. Observing the same reduction in an ontogenetic series of jaws in tyrannosaurids, we suggest that this structural strengthening of the theropod mandible over time, regardless of diet, is linked to functional adaptations acquired during ontogeny.