3D Models

The evolution of feeding performance traits is often thought to reflect adaptation to environmental pressures, but the role of constraint and trade-offs with other traits is more rarely explored. Here, we focus on feeding performance in pachycephalosaurs, a group of Late Cretaceous dinosaurs known for their cranial dome. The latter trait is thought to be a sociosexual display structure, but we hypothesize that its presence constrained the available space for jaw adductor musculature and reduced the angle of these muscles, thereby reducing feeding performance. We test this hypothesis by reconstructing the cranial musculature of five phylogenetically and temporally diverse dinosaurs: two basal ornithischians (Heterodontosaurus tucki, Lesothosaurus diagnosticus), one basal ornithopod (Hypsilophodon foxii), one basal ceratopsian (Psittacosaurus lujiatunensis), and a pachycephalosaur (Stegoceras validum). Our model of <i>Stegoceras validum</i> – the first for any pachycephalosaur – suggests that its feeding performance was much closer to that of basal ornithischians and ornithopods than expected for a derived Late Creataceous taxon, and contrary to the derived feeding performance of <i>Psittacosaurus lujiatunensis</i>, another marginocephalian. We hypothesize that sociosexual display structures in pachycephalosaurs constrained them to a more plesiomorphic low-fibre herbivore niche. This may thus constitute one of the first examples of sociosexual signalling constraining the evolution of feeding traits.