MECHANICS AND EVOLUTION OF SYNAPSID JAW
MECHANICS AND EVOLUTION OF SYNAPSID JAW
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DOI：
10.1111/j.1558-5646.1972.tb01969.x
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发表时间：
1972-01-01
期刊：
影响因子：
3.3
通讯作者：
BARGHUSEN, HR
中科院分区：
文献类型：
--
作者：
DEMAR, R;BARGHUSEN, HR
下颌和外收肌的机械安排的数学模型的构建表明，这是不太可能的，冠状突最初开发的选择，为一个更高的力臂。我们认为，相反，选择一个向后定向线的肌肉行动是最初的发展，这一进程的主要原因，这种选择与高级楔齿类的捕食习性有关。在蝶齿类中，冠状突的高度超过了一个阈值，最终允许通过进一步上升的过程来选择更高的力臂。犬齿演化的特徴是冠状突的广泛发展，然后向后迁移。该模型表明，这些都是可以理解的事件。犬齿动物的其他事件包括咬肌的发育，最初是作为外收肌的延伸，后来又增加了一个作用于前背的浅表成分。在高级犬齿兽中，咬肌发育和下颌关节上升的选择可能涉及在初级咀嚼中使用颊齿。通过使用数学模型来探索可能的进化途径来解决功能和进化问题的技术以前已经用于螺旋壳，牙齿替换和其他一些情况。这项技术有望在未来更经常地使用。
A mathematical model of the mechanical arrangement of the lower jaw and the external adductor muscle is constructed which shows that it is unlikely that a coronoid process was initially developed by selection for a higher moment arm. We believe instead that selection for a posteriorly directed line of muscle action was the primary cause for the initial development of this process, and that such selection occurred in conjunction with the predatory habits of the advanced sphenacodontids. In sphenacodontids, the height of the coronoid process was raised past a threshold and eventually allowed selection for a higher moment arm by further rise in the process to become effective. Cynodont evolution is characterized by extensive development of the coronoid process which then migrated posteriorly. The model shows that these are understandable events. Other events in cynodonts include the development of the masseter muscle, first as an extension of the external adductor, and later with an added superficial component acting anterodorsally. Selection for the development of the masseter muscle and for the rise of jaw articulation in advanced cynodonts may have involved the use of the cheek teeth in rudimentary chewing. The technique of solving functional and evolutionary problems by using mathematical models to explore possible evolutionary pathways has been used previously in coiled shells, in tooth replacement, and in a few other situations. This technique promises to be used more often in the future.