Lagomorph cranial biomechanics and the functional significance of the unique fenestrated rostrum of leporids

Abstract

The crania of leporid lagomorphs are uniquely fenestrated, including the posterior cranial bones and the lateral portion of the maxilla. The functional significance of the highly fenestrated rostrum has received considerably little attention, despite being absent in other mammalian herbivores with a long rostrum. This unique feature is of particular interest when considering functional relationships between the loading regime and cranial structure. Two primary hypotheses have been suggested: maxillary fenestrations may be associated with the transmission and redirection of incisal occlusal forces, or fenestrations may reduce skull weight to assist with manoeuvrability and increase running speed. Here we apply a comparative approach using finite element analysis to determine how the overall stress and strain environment is affected by the presence or absence of maxillary fenestrations. We compare three lagomorph species with various degrees of latticing in the fenestrated rostrum, with two macropods that do not have fenestrations. We then produce theoretical models of the three lagomorphs by filling in the fenestrated region. Our results show that the presence of fenestrations makes little difference to the overall stress experienced through the cranium and does not impact the efficiency of incisor biting. This adds to the increasing evidence that features of lagomorph cranial morphology correlate with locomotor demands, adapting to loads other than mastication. Modulating cranial mass with fenestrations may provide benefits of a lighter skull, while still providing enough surface area for muscle attachments.