Fractal Dimension and Suture Complexity During Postnatal Ontogeny in Neotropical Deer in Relation to Sexual Dimorphism and Other Biological Features

In mammals, the increase in cranial suture complexity throughout postnatal ontogeny has been linked to mechanical forces that load on the skull, including compression forces from mastication and the presence and use of cranial appendages in ungulates. Suture complexity, or interdigitation, provides a large absorptive capacity for mechanical stress. Deer are unique among ungulates by the presence of antlers only in males. In particular, Neotropical species exhibit a great diversity in terms of morphology, weight, sexual size dimorphism (absence or presence), and ecology. To evaluate the relationship of suture interdigitation with the mechanical stress produced by antlers, we quantified the complexity of the interfrontal and coronal sutures using fractal dimension (D) in six Neotropical deer species. Utilizing the occlusal tooth area (OTA) of the first upper molar as a proxy of age, we analyze changes of D throughout postnatal ontogeny and test for sexual dimorphism. In all species, ontogenetic series indicate an increase of complexity of both sutures with OTA. Overall, the species with a significant sexual dimorphism in body size and antlers with more than one tine show the more complex sutures, with the presence of greater interdigitation in adult males than in females, regardless of the existence of intraspecific fights during the rut. This is the first study where sexual dimorphism in cranial suture complexity in relation to the presence of antlers in deer is reported, suggesting the role of the interfrontal and coronal sutures on the dissipation of mechanical stress forces produced by the presence of antlers.