Chewing function and jaw articulation in fossil and extant shrews

牙齿是重建灭绝哺乳动物饮食适应的最重要信息来源。新生代哺乳动物的多样化伴随着牙齿形态的不同适应。牙齿形态发育的一个关键选择因素是摄取的食物的物理性质，这些性质可以是软的和延展性的，也可以是硬的和脆的。这些都反映在牙齿形态和咀嚼作用引起的牙齿表面的磨损面上。除了磨牙形态外，咀嚼还受到下颌关节和下颌运动的影响。磨牙形态的日益复杂(摩擦磷磨牙)伴随着下颌骨的改变，因此两种成分的准确相互作用对于食物的有效粉碎是必不可少的。下颌运动可以从面颊牙齿的磨损小平面中推断出来。牙齿形态、下颌和下颌关节的形状以及咀嚼肌肉的相互作用使有效的咀嚼食物成为可能。在拟议的项目中，这种相互作用将在化石和现存的地鼠身上进行研究。地鼠具有独特的、高度复杂的下颌关节，具有双头关节突起，由背侧和腹侧部分组成，腹侧部分在舌骨与单独的关节小面相连。假设双头关节突允许更多的分化和更复杂的下颌运动。关节突面在颅骨上的垂直排列使下颌骨有明显的前后移动。在闭合过程中观察到的下颌向外倾斜可能增加了磨牙的磨削或剪切作用。在该项目中，将使用由微型计算机断层扫描生成的高分辨率虚拟3D表面模型来模拟咀嚼周期。虚拟模拟将使用咬合指纹分析仪(OFA)软件进行，该软件已在德国福克斯公司的S研究部门开发，自那以来一直非常成功地应用于功能分析。使用OFA可以重建咀嚼周期的路径，并可以通过测量牙齿的接触面积来量化其效率。该项目的目标是更深入地了解地鼠独特的下巴发音和咀嚼运动之间的相互作用。我们假设，与关节头部分化较少的松鼠相比，关节头部明显分开的山梨树的下颌骨表现出更多的分化和复杂的运动。由于鼹鼠的磨牙形态通常是相似的，关节的形状和由此产生的颌骨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.