Ontogenetic changes in the cranial biomechanics of a crested hadrosaurid dinosaur

Mesozoic ecosystems differed from the present in the abundance of large-bodied herbivores that grew through several feeding envelopes, raising the question as to whether large-bodied adults were specialized for different resources than juveniles. Most investigations for ontogenetic resource partitioning in hadrosaurids show an ontogenetic trend towards tough plant material, but have been limited to 2D analyses of cranial shape, tooth wear, and occlusal shape. Here, we use 3D biomechanical modeling of an ontogenetic series of the hadrosaurid Corythosaurus casuarius to evaluate adaptations for resource partitioning. Results demonstrate adults had higher bite forces than juveniles and could process a wider range of materials, but jaw muscle size was negatively allometric, an uncommon trend that increased juvenile bite force and diet breadth relative to expectations for their size. Average stress and strain do not change ontogenetically, but there are changes in stress distribution. Crestless juvenile individuals exhibit a plesiomorphic stress distribution, whereas mature crested individuals experience low stress in the snout and higher stress in the braincase. This ontogenetic transition coincides with the expansion of the premaxillae and nasals to form the supracranial crest and is likely an evolutionary consequence of changes in cranial shape directing pressure away from this delicate structure.