Research Department of Cell and Developmental Biology, UCL, University College London, London, UK.
Anat Rec (Hoboken). 2012 Jul;295(7):1075-91. doi: 10.1002/ar.22487. Epub 2012 May 30.
The New Zealand tuatara, Sphenodon, has a specialized feeding system in which the teeth of the lower jaw close between two upper tooth rows before sliding forward to slice food apart like a draw cut saw. This shearing action is unique amongst living amniotes but has been compared with the chewing power stroke of mammals. We investigated details of the jaw movement using multibody dynamics analysis of an anatomically accurate three-dimensional computer model constructed from computed tomography scans. The model predicts that a flexible symphysis is necessary for changes in the intermandibular angle that permits prooral movement. Models with the greatest symphysial flexibility allow the articulation surface of the articular to follow the quadrate cotyle with the least restriction, and suggest that shearing is accompanied by a long axis rotation of the lower jaws. This promotes precise point loading between the cutting edges of particular teeth, enhancing the effectiveness of the shearing action. Given that Sphenodon is a relatively inactive reptile, we suggest that the link between oral food processing and endothermy has been overstated. Food processing improves feeding efficiency, a consideration of particular importance when food availability is unpredictable. Although this feeding mechanism is today limited to Sphenodon, a survey of fossil rhynchocephalians suggests that it was once more widespread.
新西兰大蜥蜴，楔齿蜥，有一个特殊的进食系统，其下颚的牙齿在向前滑动切开食物之前，会在下颌的两排上牙之间闭合，就像拉锯一样。这种剪切动作在现存的羊膜动物中是独一无二的，但与哺乳动物的咀嚼力冲程相比较。我们使用从计算机断层扫描构建的解剖精确的三维计算机模型的多体动力学分析来研究下颚运动的细节。该模型预测，为了允许口前运动而改变颌间角度，必须有一个灵活的联合。具有最大联合柔韧性的模型允许关节表面的关节跟随方骨髁以最小的限制，并且表明剪切伴随着下颚的长轴旋转。这促进了特定牙齿的切削刃之间的精确点加载，提高了剪切动作的效果。鉴于楔齿蜥是一种相对不活跃的爬行动物，我们认为口腔食物处理与温血之间的联系被夸大了。食物处理提高了进食效率，在食物供应不可预测时，这一点尤其重要。尽管这种进食机制今天仅限于楔齿蜥，但对化石喙头目动物的调查表明，它曾经更为广泛。
