A hundred million years in a narrow tube: The role of stabilizing selection and ecological divergence in a clade of carnivorous dinosaurs.

The vertebrate skull has undergone extensive morphological diversification and ecological specialization throughout its evolutionary history. However, the evolutionary processes shaping skull morphology in deeply-diverging lineages of non-avian theropods remain poorly understood. Here, we investigate Abelisauridae, one of the most abundant and diverse Gondwanan theropod clades that thrived for approximately 100 million years in the Mesozoic Era. Using two-dimensional geometric morphometrics and phylogenetic comparative methods, we aimed to address whether: (1) abelisaurids exhibit divergent morphologies, convergence, or phylogenetic constraints; (2) the relative influence of phylogeny, allometry, and ecology on cranial shape variation; (3) the evolutionary origins of feeding specialization within the clade; and (4) whether the observed macroevolutionary patterns are best explained by constraint, directional selection, or facilitation. Our analyses reveal that the abelisaurid skull was shaped by a complex interplay of ecological pressures, developmental constraints, and phylogenetic history. Cranial regions evolved under relatively rapid evolutionary rates with low morphological disparity, a pattern consistent with stabilizing selection. This suggests that abelisaurid skull shape evolved through directional changes constrained by developmental integration and biomechanical demands in deep time. Overall, abelisaurid cranial evolution reflects a Late Cretaceous phase of ecological specialization following a broad cranial diversification during the Jurassic.