Enamel microstructure of 34 species in eight odontocete families is described and categorized according to structural complexity (from no or prismless enamel to highly arranged enamel in decussating layers), then correlated with parameters of ecology, life history, and occlusal function. Overall, more complex dental structure in extant and extinct cetaceans is associated with smaller, more numerous teeth in taxa that bite or grasp smaller, harder prey with longer, narrower jaws and have more oral processing. Enamel complexity loosely correlates with mechanical properties, but measurement of compressive strength is complicated by the presence of cementum overlying or in place of crown enamel. Given the presence of Hunter-Schreger bands and other indices of high microstructural complexity in archaic cetaceans (with presumed plesiomorphic characters), the absence of complex enamel, as well as more generally of gross dental form, signals a loss of complexity in various cetacean lineages. Nonetheless, it is difficult to draw robust or reliable inferences regarding either cetacean phylogeny or dental function given the pattern of presumed loss of tooth complexity, and the confounding presence of numerous exceptions (taxa with complex teeth despite limited use, or with thin, weakly developed enamel and soft, simple teeth despite high occlusal function). Although retention of a complex feature implies its continued adaptive value, and thus selection for the underlying genetic and developmental bases for that complexity, loss of complexity can simply follow absence of function. Loss of complex traits presumably relates to accumulated mutations and economic efficiency, but unfolds with no distinct pattern of distribution.

中文翻译：

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鲸目动物釉质微结构：复杂性进化丧失的案例研究

根据结构复杂程度（从无牙釉质或无棱形牙釉质到交错层高度排列的牙釉质）描述和分类 8 个齿科动物 34 种物种的牙釉质微观结构，然后与生态、生活史和咬合功能参数相关联。总体而言，现存和灭绝的鲸类动物更复杂的牙齿结构与分类群中更小、更多的牙齿有关，这些牙齿咬或抓住更小、更硬的猎物，具有更长、更窄的下颚，并且具有更多的口腔处理能力。牙釉质的复杂性与机械性能松散相关，但由于牙骨质覆盖或代替牙冠牙釉质，抗压强度的测量变得复杂。鉴于在古代鲸类动物中存在 Hunter-Schreger 带和其他具有高显微结构复杂性的指数（具有假定的拟形特征），没有复杂的牙釉质，以及更普遍的牙齿形态，表明各种鲸类动物谱系的复杂性丧失。尽管如此，鉴于假定牙齿复杂性丧失的模式，以及众多异常（尽管使用有限但具有复杂牙齿的分类群，或薄而发育不全的分类群），很难对鲸类系统发育或牙齿功能做出强有力的或可靠的推论。牙釉质和柔软、简单的牙齿，尽管具有很高的咬合功能）。尽管保留复杂特征意味着其持续的适应性价值，从而为该复杂性选择潜在的遗传和发育基础，但复杂性的丧失可能只是在功能缺失之后。复杂性状的丧失可能与累积的突变和经济效率有关，