MECHANICS AND THE EVOLUTION OF THE SYNAPSID JAW
MECHANICS AND THE EVOLUTION OF THE SYNAPSID JAW
复制标题
联孔类下颌的力学和进化
DOI：
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发表时间：
1972
期刊：
影响因子：
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通讯作者：
Herbert R. Barghusen
中科院分区：
文献类型：
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作者：
R. Demar;Herbert R. Barghusen
在过去的十年或更长的时间里，已经重建了许多化石脊椎动物分类群的下颌内收肌组织。从这些重建，颌骨力学的启发性研究已经发展起来，包括对完全灭绝的群体的解释。在许多这样的研究中，根据其特殊的力学特性，已经提出了下颌内收肌组织的特定排列可能的适应性作用。然而，很少有人注意到机械转变的细节在不断发展的颚系统。本文讨论了从原始爬行动物到早期哺乳动物颌部机械操作的变化。外内收肌的变化主导着下颌突触肌的进化。为了建立这些变化的数学模型，我们主要基于Barghusen（1966,1972）在一系列突触形态阶段的重建和结论，对肌肉的作用线、肌肉附着面积和颌骨系统的一般操作进行了假设。Olson （1961, p. 209）将早期四足动物颚部力学分为两个基本系统：(1)运动惯性系统，(2)静压系统。基于这一分析，他定义了不同化石类型之间摄食行为的差异。也就是说，那些具有运动惯性系统的动物依靠大张着的下颚所受的巨大肌肉力。一旦运动是由这些力发起的，下巴的速度和质量是有效的喂食。根据奥尔森的说法，当下颌关闭或接近关闭时，很少有肌肉力量被传递给下颌。相比之下，静压系统依赖于肌肉力施加于颌骨时，它是在咬合或近咬合的位置。由于本文讨论的突触类爬行动物似乎有大量的下颌内收肌组织，因此当颌闭合时，牙齿排的闭合力最大，因此我们所关注的类群属于奥尔森静压系统。然而，在这里所考虑的组中，内收肌组织排列的功能和适应性意义可能不仅仅是颌闭合时力的最大化。Ostrom（1964）得出结论，冠突的发展（和/或下颌关节的凹陷）导致下颌外肌肉组织力臂长度的增加。因此，当施加在冠突上的力有一个后鼻线并以小于90度的角度作用于下颌时，内收力（扭矩）就会增加。冠突的进化起源和进一步发展在突触谱系中外收肌的进化及其机械能力中起着主导作用。因此，我们感兴趣的是，确定可能的选择压力负责突触体冠状过程的发展和进化。
Over the past decade or more, adductor jaw musculature has been reconstructed for a number of fossil vertebrate taxa. From these reconstructions, enlightening studies of jaw mechanics have been developed, including interpretations in totally extinct groups. In many such studies, the possible adaptive role of specific arrangements of adductor jaw musculature has been proposed based on their special mechanical properties. However, little attention has been given to the details of the mechanical transformations within evolving jaw systems. This paper concerns alterations in the mechanical operation of the jaw from primitive reptiles to early mammals. Changes in the external adductor musculature dominate the evolution of synapsid jaw musculature. In order to construct a mathematical model of these changes, we have made assumptions concerning the line of muscle action, area of muscle attachment, and general operation of the jaw system based mainly on the reconstructions and conclusions of Barghusen (1968, 1972) in a series of synapsid morphological stages. Olson (1961, p. 209) has divided early tetrapod jaw mechanics into two basic systems: (1) the kinetic inertial system, and (2) the static pressure system. Based on this analysis, he defined differences in feeding behavior among fossil types. That is, those animals possessing the kinetic inertial system depend upon large muscular forces imparted to the lower jaw when it is widely open. Once motion is initiated by these forces, the velocity and mass of the jaw is effective in feeding. Little muscular force, according to Olson, is imparted to the lower jaw when it is closed or nearly closed. In contrast, the static pressure system depends upon muscular forces applied to the jaw when it is in occlusal or near-occlusal position. Since the synapsid reptiles discussed in this paper appear to have a significant amount of their adductor jaw musculature arranged so that the closing force at the tooth row is maximized when the jaws are closed, the groups we are concerned with fall into Olson's static pressure system. However, it is probable that the functional and adaptive significance of the arrangement of adductor musculature in the groups considered here involves more than maximization of forces when the jaw is closed. Ostrom (1964) concluded that the development of a coronoid process (and/or depression of the jaw articulation) results in an increase in the length of the moment arm of the external jaw musculature. Thus, an increase in adductive force (torque) is achieved when the force applied to the coronoid process has a posterodorsal line of action and acts on the lower jaw at some angle less than 90 degrees. The evolutionary origin and further development of a coronoid process plays a dominant role in the evolution of the external adductor jaw musculature and its mechanical capabilities in the synapsid lineages examined here. We are interested, therefore, in defining the possible selection pressures responsible for the development and evolution of the synapsid coronoid process.