Sharp Alana C, Rich Thomas H
School of Science and Technology, University of New England, Armidale, New South Wales, Australia.
School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria, Australia.
J Anat. 2016 Jun;228(6):984-95. doi: 10.1111/joa.12456. Epub 2016 Mar 3.
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.
巨型已灭绝有袋动物双门齿兽（Diprotodon optatum）的头骨形态与其体型并不匹配，其头骨由非常薄的骨骼和占据大部分颅腔内部空间的大颅窦组成。由于没有现存的有袋动物类似物，这些窦的功能尚不清楚。采用有限元方法来识别高应力和低应力区域，并估计双门齿兽的咬合力，以检验关于广泛颅窦功能的假设。制作了详细的颅骨、下颌骨和咬肌三维模型。此外，对双门齿兽颅骨模型进行了操作，以研究头骨和窦结构的变化，包括一个没有窦的模型（窦被骨“填充”）和一个有矢状嵴的模型。结果表明，双门齿兽的颅窦显著减轻了头骨重量，同时仍提供结构支撑、高咬合力和低应力，这表明颅骨可能能够承受比进食时产生的负荷更高的负荷。本研究的数据支持这样的假设，即气化是由生物力学负荷驱动的，并且发生在低应力区域。窦的存在可能是由于包括大脑和大型咬肌（尤其是颞肌）在内的软组织需求，导致头骨外表面与脑壳分离的副产品。在像双门齿兽这样的非常大的物种中，这种分离更为明显，由于与头骨大小相比相对较小的大脑，导致广泛的颅窦。
