Enamel dentition microstructure of Mariliasuchus amarali (Crocodyliformes, Notosuchia), from the Upper Cretaceous (Turonian–Santonian) of the Bauru Basin, Brazil

Abstract

Advanced notosuchians represent a diverse clade of highly heterodont crocodyliforms that were endemic to the South American landmass during the Cretaceous. Mariliasuchus amarali is an advanced notosuchian from the Upper Cretaceous (Turonian–Santonian) of the Bauru Basin, south-central Brazil, and it is known from several well-preserved specimens in distinct ontogenetic stages. Previous functional analyses of the dentition of M. amarali suggested generalist feeding habits. However, microscopic patterns of the enamel, such as crystallite micromorphology and microwear variation along the dental series, have not been investigated in detail so far. Our results evidence that M. amarali enamel is unique among crocodyliforms, and that heterodonty in this species is even more complex than previously thought. External crown morphology, macrowear position, microwear orientation, and enamel crystallite micromorphology support the recognition of four tooth morphotypes, each of these presenting a combination of features never seen before. M. amarali is the first described reptile bearing both true and false denticles in the same tooth, a condition up to now autapomorphic for the taxon that supports its classification into a distinct dental category (ziphomorph). Ontogenetic trends of dentition reveal that heterodonty was kept through the entire life of M. amarali, and that adults and juveniles occupied very similar ecological niches. Hypothesis of M. amarali presenting omnivorous feeding habits, with the inclusion of hard items in its diet, is supported here. The unique combination of dental features in the taxon could have provided an important adaptive advantage in a low resource environment, as it has been postulated for the Bauru Basin.