Cranial anatomy of Acynodon adriaticus and extreme durophagous adaptations in Eusuchia (Reptilia: Crocodylomorpha).

Acynodon adriaticus, a small eusuchian from the Late Cretaceous of Italy, is known for its well-preserved cranial and postcranial material. Despite its excellent preservation, many details remain hidden due to the physical overlap between the elements and matrix obliteration. We used Micro-CT scans to reveal previously overlooked anatomical features and describe in detail the cranial and dental anatomy of this taxon, shedding new light on its palaeoecology. The holotypic specimen, SC 57248, represents a mature individual exhibiting signs of hyperossification, developed ornamentation, and various pathologies, including jaw arthritis and a possible dental anomaly. Acynodon adriaticus exhibits significant durophagous adaptations, including a robust, brevirostrine skull optimized for powerful biting and stress-load capacity. Its specialized dentition, lacking caniniform teeth, features anterior chisel-like teeth and hypertrophic posterior molariforms with thick enamel, indicative of a diet specializing in hard-shelled prey. The dentition pattern, accelerated molariform replacement rate, and reduced orbit size suggest adaptations for durophagous foraging in turbid, densely vegetated aquatic environments. The paleoecological context during the Late Cretaceous, characterized by increased freshwater habitats and high invertebrate diversity, likely facilitated the evolution of such specialized traits in A. adriaticus. This small crocodylomorph likely foraged slowly in shallow, benthic environments, using its powerful bite to process mollusks and large arthropods. The study of A. adriaticus, along with comparisons with other crocodylomorphs and ecomorphologically similar taxa like Iharkutosuchus makadii and Gnatusuchus pebasensis, provides a valuable morphofunctional model for understanding the evolutionary pathways of extinct crocodylians to durophagy.