Mechanical significance of ammonoid septa with complex sutures
Mechanical significance of ammonoid septa with complex sutures
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具有复杂缝线的菊石隔膜的力学意义
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
G. Westermann
中科院分区：
文献类型：
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作者：
R. Hewitt;G. Westermann
前和后世纪的假设有关静水压力的缝合复杂性的机械功能进行了比较。这些旧的思想催生了19世纪的“世纪巴克兰假说”，而这又在很大程度上与“韦斯特曼模型”同义。巴克兰（1836）假设，有凹槽的隔膜支撑着膜锥壁的薄弱侧面。引入了两个新的参数来定义由横截面中相邻凸角和鞍形槽之间的距离所限定的壁侧面的圆柱段的强度之间的协变。壁强度指数（IWS）和这个反支撑角（伊萨）的乘积预测了无限长圆柱体中的屈曲压力，这意味着盘绕的鹦鹉螺比明显较弱的氧锥状菊石更容易通过其螺纹侧面内爆。广泛使用的缝合线复杂性指数（ISC）测量了边缘裂缝，边缘裂缝掩盖了这种趋势，并作为强壁和弱壁的弹性床。然而，ISC是更成比例的栖息地深度比屈曲压力时，所有其他因素都是恒定的。每个带槽隔片的中心厚度与隔片跨越的距离和在“最后隔片”位置上的静水压力成正比地增加。边缘厚度保持在一个更恒定的值，这使得缝合线越来越像一个弹簧或减震器，因为壁厚在个体发育过程中扩大。因此，两者的比例，中心和边缘厚度和密切相关的ISC之间，随着壳直径和栖息地深度增加。
Pre- and post-19th century hypotheses relating hydrostatic pressure to the mechanical function of sutural complexity are compared. The old ideas gave rise to the 19th century ‘Buckland hypothesis’, which is in turn largely synonymous with the ‘Westermann model’. Buckland (1836) postulated that fluted septa buttressed the weak flanks of the phragmocone wall. Two new parameters are introduced to define the covariation between the strength of cylindrical segments of the wall flank bounded by the distance between adjacent lobe and saddle-flutes in transverse sections. The product of the index of wall strength (IWS) and this inverse support angle (ISA) predicts the buckling pressure in a cylinder of infinite length, and it implies that coiled nautiloids were more likely to be imploded via their whorl flanks than the apparently weaker oxyconic ammonoids. The widely used index of sutural complexity (ISC) measures the marginal corrugation which obscures this trend and acts as an elastic bed for both strong and weak walls. However, the ISC is more proportional to habitat depth than the buckling pressure when all other factors are constant. The central thickness of each fluted septum was increased in direct proportion to the distance spanned by the septum and the hydrostatic pressure on it in the ‘last septum’ position. The marginal thickness was maintained at a more constant value, which permitted the suture to increasingly act like a spring or shock absorber, as the wall thickness was enlarged during ontogeny. Both the ratios, between the central and marginal thicknesses and the closely related ISC, therefore, increased with shell diameter and habitat depth.