Building a predator: macroevolutionary patterns in the skull of abelisaurid dinosaurs

Abstract

Abelisauridae is the most abundant and well-known clade of Gondwanan theropods, characterized by uniquely tall, robust and heavily ornamented skulls. Different processes have been proposed to explain the evolution of the abelisaurid skull based on anatomical and biomechanical studies, but a quantitative analysis under an explicit macroevolutionary approach is lacking. In this study, we assess patterns of modularity, integration and macroevolutionary trends of the abelisaurid skull by quantifying different cranial regions and bones using two-dimensional geometric morphometrics. Our results reveal phylogenetic modularity and evolutionary integration between the neurocranium and rostral regions. High disparity and evolutionary rates are found in the occipital region, squamosal, quadratojugal, lacrimal and postorbital. These findings suggest that the neurocranium was the main region involved in the proportional cranial height increase in Abelisauridae. The observed patterns are linked to different feeding strategies, supporting ecological specialization within this theropod lineage. We propose that ecological pressures were the main drivers of skull evolution in abelisaurids, with some features co-opted for socio-sexual display. Future research should focus on evolutionary modelling to investigate patterns of evolutionary rate selection and constraints that can explain the diversification of the skull shape of this clade during the Cretaceous.