Dental histology of Guarinisuchus munizi (Crocodylomorpha, Dyrosauridae)

Guarinisuchus munizi, a Paleocene dyrosaurid crocodyliform from the Maria Farinha Formation (Paraíba Basin, Brazil), survived the Cretaceous–Palaeogene mass extinction. While macromorphology suggests piscivory, its dietary flexibility remains unclear. This study presents the first histological analysis of G. munizi dentition, examining 11 teeth from multiple available specimens (10 isolated, one from jaw fragment) using standard thin-section techniques. Enamel thickness ranges from 0.05–0.13 mm, with thinner enamel (~0.05 mm) indicating soft-tissue piercing and thicker enamel (~0.13 mm) suggesting dietary versatility including hard-shelled prey. Hunter-Schreger bands (HSB) in enamel enhance fracture resistance under polarised light. Dentine deposition rates (von Ebner Incremental Width, VEIW: 3–42 µm) show high variability, exceeding uniformity in most crocodyliforms and likely reflecting environmental sensitivity to seasonal water temperature and resource fluctuations in the Paraíba Basin. This metabolic flexibility underscores Dyrosauridae’s post-K-Pg adaptive capacity. Combined enamel microstructure and growth-line variation suggest functional differentiation and individual diversity. Our findings demonstrate dental histology’s value for reconstructing extinct crocodyliform palaeoecology, establishing a foundation for dyrosaurid research.