Chewing function and jaw articulation in fossil and extant shrews

牙齿是重建已灭绝哺乳动物饮食适应性的最重要信息来源。新生代哺乳动物的多样化伴随着牙齿形态的多样化适应。牙齿形态发育的一个关键选择因素是所摄入食物的物理性质，其范围可以从柔软和延展性到坚硬和脆性。这些都反映在牙齿的形态和磨损面在牙表面引起的咀嚼作用。除了磨牙形态外，咀嚼还受下颌关节和下颌骨运动的影响。磨牙形态（摩擦磨牙）的日益复杂伴随着下颌骨的变化，因此这两种成分的确切相互作用对于有效粉碎食物是必不可少的。下颌的运动可以从颊齿的磨损面中推断出来。有效的咀嚼食物是由牙齿形态、下颌骨的形状和颌关节以及咀嚼肌肉组织的相互作用而实现的。在拟议的项目中，这种相互作用将在化石和现存的鼩鼱中进行研究。鼩鼱有一个独特的，高度复杂的下颌关节，有一个双头关节过程，由背侧和腹侧组成，在鳞片上有单独的关节面。假设双头关节突允许更多分化和更复杂的下颌运动。关节突在颅骨处的垂直排列使得下颌骨有明显的前后运动。闭合时观察到的下颌向外倾斜可能增加了磨牙的磨磨或剪切作用。在该项目中，咀嚼周期将通过微计算机断层扫描生成的高分辨率虚拟3D表面模型进行模拟。虚拟模拟将使用咬合指纹分析仪（OFA）软件进行，该软件是由德国研究部门开发的，自那时以来一直非常成功地应用于功能分析。利用OFA可以重建咀嚼循环的路径，并可以通过测量牙齿的接触面积来量化咀嚼循环的效率。该项目的目标是更深入地了解鼩鼱独特的颚关节和咀嚼运动之间的相互作用。我们假设具有明显分离的关节头的鼩鼱的下颌骨比具有不太明显区分的关节头的鼩鼱的下颌骨表现出更多的分化和复杂的运动。由于鼩鼱的臼齿形态大体相似，因此关节的形状和由此产生的下颌运动应该可以从磨损面和条纹中推断出来。

Teeth are the most important source of information for reconstructing the dietary adaptations of extinct mammals. The diversification of mammals during the Cenozoic was accompanied by diverse adaptations of tooth morphologies. A crucial selection-factor for the development of the tooth morphology are the physical properties of the ingested food which can range from soft and ductile to hard and brittle. These are reflected in tooth morphology and the wear facets on the dental surface caused by the chewing action. Besides molar morphology, chewing is influenced by the jaw articulation and motion of the mandible. The increasing complexity of molar morphology (tribosphenic molar) is accompagnied by modifications of the mandible, whereby the exact interplay of both components is essential for an efficient comminution of the food. Mandibular movements can be deducted from wear facets on the cheek teeth. An efficient mastication of food is enabled by the interplay of tooth morphology, shape of the mandible and jaw articulation, and the chewing musculature. In the proposed project this interaction shall be studied in fossil and extant shrews. Shrews have a unique, highly complex mandibular articulation, with a double-headed articular process that consists of a dorsal and a ventral part that articulate with separate articulation facets at the sqamosal. It is assumed that the double-headed articular process allows for more differentiated and more complex mandibular movements. The vertical arrangement of the glenoid facet at the skull allows for a distinct anterior- posterior movement of the mandible. The observed outward tilt of the lower jaw during closure might have increased the grinding or shearing action of the molars. In the project the masticatory cycle will be simulated with high-resolution virtual 3D surface models generated by micro computed tomography. The virtual simulation will be performed with the Occlusal Fingerprint Analyzer (OFA) software that has been developed in the Deutsche Forschungsgemeinschaft´s research unit and which has been very successfully applied for functional analyses since then. With the OFA the path of the masticatory cycle can be reconsructed and its efficiency can be quantified by measurement of the contact areas of the teeth. Goal of the project is a deeper understanding of the interplay between the unique jaw articulation and chewing movements in shrews. We hypothesize that the mandibles of soricine shrews that have clearly separated articular heads perform more differentiated and complex movements that the crocidurine shrews with less clearly differentiated articular heads. Since the molar morphology is generally similar in shrews, the shape of the articulation and the resulting jaw movements should be deductable from the wear facets and striations.