Interfrontal Suture Interdigitation Throughout Postnatal Ontogeny in Marsh Deer in Relation to the Presence, Localization, and Size of Antlers

ABSTRACT

Marsh deer Blastocerus dichotomus is a Neotropical cervid characterized by sexual dimorphism in body size and the presence of heavy and massive antlers in males, with a dichotomous branching pattern. Antlers are placed on the frontal bones close to the coronal suture in the calvaria, generating mechanical stress. In mammals, cranial sutures develop interdigitation during postnatal ontogeny, which allows the absorption and distribution of the mechanical forces generated along the skull. As the interfrontal suture occupies the rostral and calvaria regions, we characterized its interdigitation in order to relate it with the presence and position of antlers as a source of mechanical stress exclusive to males. We partitioned this suture into six sections of equal length and distinct proximity to the antlers and quantified their interdigitation using the fractal dimension (FD). We evaluated differences in interdigitation among sections with a linear mixed effects model and the interdigitation of each one throughout ontogeny, utilizing the occlusal surface area of upper M1 as a proxy of age. Additionally, we examined the morphology of each section by sex, comparing adults only. Rostral sections maintain a straight morphology during ontogeny, whereas from the second third of the suture pathway, they differ in their interdigitation. Higher FD values are obtained with increasing proximity to antlers, accompanied by the development of sexual dimorphism with greater interdigitation in males. These results support the hypothesis of a relationship between the interdigitation of the interfrontal suture and the mechanical loads caused by antlers on the skull of B. dichotomus .