Abstract
The Dinosaur Park Formation (DPF) of western Canada is well known for its diverse fossil assemblage, preserving over a dozen species of large-bodied herbivorous dinosaurs. The high density of large herbivores has raised questions of how these animals were able to coexist and limit competition, leading to several studies investigating the potential for resource partitioning. In the DPF, hadrosaurids are of particular ecological significance because of their abundance, diversity and complex feeding system. Here, we used 3D muscle reconstructions and finite-element analysis to evaluate the mechanical performance of the cranium and lower jaws of the lambeosaurine Corythosaurus casuarius and the contemporaneous hadrosaurine Gryposaurus notabilis to test for the potential of resource partitioning. We found G. notabilis had larger adductor muscles than similarly sized C. casuarius, but the latter had greater mechanical efficiency, resulting in similar bite forces for similarly sized animals. The cranium of C. casuarius is more resistant to bending than G. notabilis and exhibits a derived stress distribution that is probably associated with the supracranial crest. Resource partitioning between these taxa would have been primarily size-mediated, where larger G. notabilis would have been able to process tougher plant material than smaller C. casuarius at equivalent ontogenetic stages.