Cranial biomechanics, bite force and function of the endocranial sinuses in Diprotodon optatum, the largest known marsupial

Abstract

The giant extinct marsupial Diprotodon optatum has unusual skull morphology for an animal of its size, consisting of very thin bone and large cranial sinuses that occupy most of the internal cranial space. The function of these sinuses is unknown as there are no living marsupial analogues. The finite element method was applied to identify areas of high and low stress, and estimate the bite force of Diprotodon to test hypotheses on the function of the extensive cranial sinuses. Detailed three-dimensional models of the cranium, mandible and jaw adductor muscles were produced. In addition, manipulations to the Diprotodon cranial model were performed to investigate changes in skull and sinus structure, including a model with no sinuses (sinuses 'filled' with bone) and a model with a midsagittal crest. Results indicate that the cranial sinuses in Diprotodon significantly lighten the skull while still providing structural support, a high bite force and low stress, indicating the cranium may have been able to withstand higher loads than those generated during feeding. Data from this study support the hypothesis that pneumatisation is driven by biomechanical loads and occurs in areas of low stress. The presence of sinuses is likely to be a byproduct of the separation of the outer surface of the skull from the braincase due to the demands of soft tissue including the brain and the large jaw adductor musculature, especially the temporalis. In very large species, such as Diprotodon, this separation is more pronounced, resulting in extensive cranial sinuses due to a relatively small brain compared with the size of the skull.

Biomechanical simulations reveal a trade-off between adaptation to glacial climate and dietary niche versatility in European cave bears

“…This is also the case in T. ornatus, but its values of im∆SEa are only slightly higher than one. This is notable because the main function of the sinuses is thought to be involved in stress dissipation during feeding and to provide skull structural stability (20)(21)(22). However, the analyses of von Mises stress in M. ursinus and U. americanus reveal higher stresses in models with sinuses than in models without sinuses (Figs.…”

“…To test whether the extremely developed sinuses in the cave bear influence its biomechanical performance for feeding behavior, we eliminated virtually the paranasal sinuses by filling the cavities with artificial bone material using Geomagic (21,22). The sinuses have a potential dual effect on feeding biomechanics (i) for having large empty spaces in the paranasal cavities and (ii) for the appearance of a dome as a consequence of sinus inflation on the frontal area.…”

Material properties of the skull layers of the primate parietal bone: A single-subject study

“…Thus, special attention is needed when trying to predict the biomechanical response of the craniofacial skeleton of extinct species [12]. The individual mechanical properties of the calvarial three-layered system are relevant to understand not only the functional response of the skull, but also its biomechanics, so clinical, functional, and anthropological models of the skull may be evaluated properly [31][32][33]. Additionally, understanding of the mechanical properties of the components of the cranial vault would make possible the development of better synthetic bone substitutes for the cranium [34].…”

“…On the other hand, several finite element models (FEM) of the skull have been built using the information available for the engineering sandwich structure and the available mechanical properties. Consequently, most of the FEM of the skull can be grouped into one of four categories: (1) FEM of the skull built using a single isotropic material for an averaged layer in the entire calvarial structure [32]. (2) FEM of the skull including an anisotropic condition of the material for a single layered structure [37].…”

Peer Review #1 of "Probabilistic biomechanical finite element simulations: whole-model classical hypothesis testing based on upcrossing geometry (v0.1)"

“…Yet, typically stress and strain values are only reported and analysed from just a few elements (Porro et al, 2013;Fitton et al, 2012a). Alternatively average or peak stress or strain values can be computed for whole models (Dumont et al, 2011;Cox et al, 2012;Parr et al, 2013;Sharp and Rich, 2016) or selected regions (Wroe et al, 2007a,b;Nakashige et al, 2011).…”