Craniofacial lesions in the earliest predatory dinosaurs indicate intraspecific agonistic behaviour at the dawn of the dinosaur era.

Herrerasauridae were among the first large carnivorous dinosaurs. Although their anatomy and phylogenetic relationships have been previously studied, little is known about their paleobiology. Bone pathologies provide clues about the behaviour of ancient organisms, and this study evaluates presumed craniofacial pathologies in herrerasaurid specimens to infer their etiology and implications. Our analysis reveals that the craniofacial marks analysed are most likely pathological in nature and possibly result from intraspecific agonistic interactions, rather than post-mortem alterations. The relatively high frequency of lesions identified supports this claim. In the sample of herrerasaurids with preserved skulls analysed, nearly half presented craniofacial lesions. The bone traumas identified here are the oldest evidence of pathology in dinosaurs. Identification and analysis of pathologies in early dinosaurs can provide insights into their paleobiology and evolution of behavioural characteristics.