Establishing a framework for archosaur cranial mechanics
Establishing a framework for archosaur cranial mechanics
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DOI：
10.1666/07006.1
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发表时间：
2008-11
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影响因子：
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通讯作者：
E. Rayfield;A. Milner
中科院分区：
文献类型：
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作者：
E. Rayfield;A. Milner
摘要 本次分析的目的是建立简单的祖龙颅骨形态的基本力学原理。我们特别评估了祖龙的两个关键创新，即副腭和眶窗，对咬合引起的负载的最佳阻力的影响。虽然这种简化的模型不能替代更复杂的颅骨几何形状，但它们可以作为一个明确的基准，可以作为未来纳入更复杂几何形状的研究的参考点。我们创建了有限元 (FE) 模型，其中包括高大的圆顶（前喙）口鼻部或宽阔、扁平（扁口）古龙口鼻部。在对牙列施加咬合载荷后，在有或没有第二腭和/或眶窗孔的模型中记录峰值冯米塞斯应力。我们检查了沿颌骨的一系列咬合位置的双边弯曲和单侧扭转诱导咬合，并对材料特性进行了敏感性分析。不同有限元形态类型之间的成对比较表明，口角模型比其对应的颈口模型更强。口吻模型在弯曲方面也比在扭转方面更强，而扁口模型同样容易受到任一载荷类型的影响。正如预期的那样，我们发现具有窗孔的模型总是具有最大的峰值应力，因此推断其“较弱”，在前口形式和前咬合扁口形式中尤其如此。令人惊讶的是，尽管添加上颚总是会降低峰值应力，但这很少会大幅降低，并且在双侧弯曲咬合中并不显着。在单侧扭转诱发咬合中，上颚更为重要。从这些简单的模型中可以得出祖龙颅骨结构的两个基本原理：（1）具有窗孔的形态在咬合方面的构造不是最理想的，（2）上颚的存在或不存在对于单侧咬合动物的颅骨完整性至关重要。将这些结果推断到古龙颅骨进化，似乎如果机械优化是颅骨形状所依据的唯一标准，那么理论上大多数古龙可以强化其颅骨以增加对咬合力的抵抗力。然而，这些强化的形态类型通常在化石记录中观察不到，因此古龙似乎受到各种非机械形态的限制。例如，肉食性兽脚亚目恐龙尽管产生较大的咬合力，但由于颅面骨化和气化之间的相互作用，可能会保留较大的次优窗孔。此外，现存的鳄鱼似乎以最有效的方式通过上颚和填充的窗孔来强化其头骨，尽管可能受到流体动力学因素的限制，使其成为较弱的扁口形态类型。未来的挑战是确定当更详细地探索复杂颅骨几何形状的生物力学时，这些简单的预测是否成立。
Abstract The aim of this analysis was to establish the basic mechanical principles of simple archosaur cranial form. In particular we estimated the influence of two key archosaur innovations, the secondary palate and the antorbital fenestra, on the optimal resistance of biting-induced loads. Although such simplified models cannot substitute for more complex cranial geometries, they can act as a clearly derived benchmark that can serve as a reference point for future studies incorporating more complex geometry. We created finite element (FE) models comprising either a tall, domed (oreinirostral) snout or a broad, flat (platyrostral) archosaur snout. Peak von Mises stress was recorded in models with and without a secondary palate and/or antorbital fenestra after the application of bite loads to the tooth row. We examined bilateral bending and unilateral torsion-inducing bites for a series of bite positions along the jaw, and conducted a sensitivity analysis of material properties. Pairwise comparison between different FE morphotypes revealed that oreinirostral models are stronger than their platyrostral counterparts. Oreinirostral models are also stronger in bending than in torsion, whereas platyrostral models are equally susceptible to either load type. As expected, we found that models with a fenestra always have greatest peak stresses and by inference are “weaker,” significantly so in oreinirostral forms and anterior biting platyrostral forms. Surprisingly, although adding a palate always lowers peak stress, this is rarely by large magnitudes and is not significant in bilateral bending bites. The palate is more important in unilateral torsion-inducing biting. Two basic principles of archosaur cranial construction can be derived from these simple models: (1) forms with a fenestra are suboptimally constructed with respect to biting, and (2) the presence or absence of a palate is significant to cranial integrity in unilaterally biting animals. Extrapolating these results to archosaur cranial evolution, it appears that if mechanical optimization were the only criterion on which skull form is based, then most archosaurs could in theory strengthen their skulls to increase resistance to biting forces. These strengthened morphotypes are generally not observed in the fossil record, however, and therefore archosaurs appear subject to various non-mechanical morphological constraints. Carnivorous theropod dinosaurs, for example, may retain large suboptimal fenestra despite generating large bite forces, owing to an interplay between craniofacial ossification and pneumatization. Furthermore, living crocodylians appear to strengthen their skull with a palate and filled fenestral opening in the most efficient way possible, despite being constrained perhaps by hydrodynamic factors to the weaker platyrostral morphotype. The future challenge is to ascertain whether these simple predictions are maintained when the biomechanics of complex cranial geometries are explored in more detail.