Zoology Division, School of Environmental and Rural Sciences, University of New England, Armidale, New South Wales, Australia.
Department of Anthropology, University of Arkansas, Fayetteville, Arkansas, United States of America.
PLoS One. 2019 Sep 11;14(9):e0221287. doi: 10.1371/journal.pone.0221287. eCollection 2019.
The Sthenurinae were a diverse subfamily of short-faced kangaroos that arose in the Miocene and diversified during the Pliocene and Pleistocene. Many species possessed skull morphologies that were relatively structurally reinforced with bone, suggesting that they were adapted to incorporate particularly resistant foods into their diets. However, the functional roles of many unique, robust features of the sthenurine cranium are not yet clearly defined. Here, the finite element method is applied to conduct a comprehensive analysis of unilateral biting along the cheek tooth battery of a well-represented sthenurine, Simosthenurus occidentalis. The results are compared with those of an extant species considered to be of most similar ecology and cranial proportions to this species, the koala (Phascolarctos cinereus). The simulations reveal that the cranium of S. occidentalis could produce and withstand comparatively high forces during unilateral biting. Its greatly expanded zygomatic arches potentially housed enlarged zygomaticomandibularis muscles, shown here to reduce the risk of dislocation of the temporomandibular joint during biting with the rear of a broad, extensive cheek tooth row. This may also be a function of the zygomaticomandibularis in the giant panda (Ailuropoda melanoleuca), another species known to exhibit an enlarged zygomatic arch and hypertrophy of this muscle. Furthermore, the expanded frontal plates of the S. occidentalis cranium form broad arches of bone with the braincase and deepened maxillae that each extend from the anterior tooth rows to their opposing jaw joints. These arches are demonstrated here to be a key feature in resisting high torsional forces during unilateral premolar biting on large, resistant food items. This supports the notion that S. occidentalis fed thick, lignified vegetation directly to the cheek teeth in a similar manner to that described for the giant panda when crushing mature bamboo culms.
短面袋鼠亚科是一类多样化的短面袋鼠，起源于中新世，在更新世和更新世期间多样化。许多物种的头骨形态结构相对坚固，表明它们适应将特别有抵抗力的食物纳入其饮食中。然而，许多斯特努林头骨的独特、强壮特征的功能作用尚未明确界定。在这里，有限元法被应用于对一个具有代表性的斯特努林物种，即西蒙袋鼠（Simosthenurus occidentalis）的颊齿电池进行单侧咀嚼的综合分析。结果与被认为与该物种生态和颅骨比例最相似的现生物种（树袋熊，Phascolarctos cinereus）的结果进行了比较。模拟结果表明，西蒙袋鼠的头骨在单侧咀嚼时可以产生并承受相对较高的力。其大大扩展的颧骨弓可能容纳了扩大的颧骨下颌肌，这里显示出在咀嚼宽阔、广泛的颊齿列的后端时，减少颞下颌关节脱位的风险。这也可能是大熊猫（Ailuropoda melanoleuca）中颧骨下颌肌的功能，大熊猫是另一种已知具有扩大的颧骨弓和该肌肉肥大的物种。此外，西蒙袋鼠头骨的扩展额骨板与脑壳和加深的上颌骨一起形成宽阔的骨拱，从前牙列延伸到其相对的颌关节。这些拱在这里被证明是抵抗单侧前磨牙咀嚼大而有抵抗力的食物时高扭转力的关键特征。这支持了这样一种观点，即西蒙袋鼠以类似于描述大熊猫粉碎成熟竹茎时的方式，将厚的、木质化的植物直接喂给颊齿。
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