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首页> 外文期刊>PLoS One >Enamel Ultrastructure in Fossil Cetaceans (Cetacea: Archaeoceti and Odontoceti)
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Enamel Ultrastructure in Fossil Cetaceans (Cetacea: Archaeoceti and Odontoceti)

机译：化石鲸类中的牙釉质超微结构（鲸类：古生动物和齿形动物）

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The transition from terrestrial ancestry to a fully pelagic life profoundly altered the body systems of cetaceans, with extreme morphological changes in the skull and feeding apparatus. The Oligocene Epoch was a crucial time in the evolution of cetaceans when the ancestors of modern whales and dolphins (Neoceti) underwent major diversification, but details of dental structure and evolution are poorly known for the archaeocete-neocete transition. We report the morphology of teeth and ultrastructure of enamel in archaeocetes, and fossil platanistoids and delphinoids, ranging from late Oligocene (Waitaki Valley, New Zealand) to Pliocene (Caldera, Chile). Teeth were embedded in epoxy resin, sectioned in cross and longitudinal planes, polished, etched, and coated with gold palladium for scanning electron microscopy (SEM) observation. SEM images showed that in archaeocetes, squalodontids and Prosqualodon (taxa with heterodont and nonpolydont/limited polydont teeth), the inner enamel was organized in Hunter-Schreger bands (HSB) with an outer layer of radial enamel. This is a common pattern in most large-bodied mammals and it is regarded as a biomechanical adaptation related to food processing and crack resistance. Fossil Otekaikea sp. and delphinoids, which were polydont and homodont, showed a simpler structure, with inner radial and outer prismless enamel. Radial enamel is regarded as more wear-resistant and has been retained in several mammalian taxa in which opposing tooth surfaces slide over each other. These observations suggest that the transition from a heterodont and nonpolydont/limited polydont dentition in archaeocetes and early odontocetes, to homodont and polydont teeth in crownward odontocetes, was also linked to a marked simplification in the enamel Schmelzmuster. These patterns probably reflect functional shifts in food processing from shear-and-mastication in archaeocetes and early odontocetes, to pierce-and-grasp occlusion in crownward odontocetes, with the implication of less demanding feeding biomechanics as seen in most extant odontocetes.
机译：从陆地祖先到完全上层鱼类的过渡极大地改变了鲸类动物的身体系统，头骨和饲喂装置的形态发生了极大的变化。渐新世时期是鲸类动物进化的关键时期，现代鲸鱼和海豚的祖先（新鲸）经历了主要的多样化，但是对于牙齿的结构和演化的细节却鲜为人知。我们报道了从始新世（新西兰怀塔基谷地）到上新世（上新世）（智利卡尔德拉），古生代足齿，化石类扁桃体和飞蝶类中牙齿的形态和釉质的超微结构。将牙齿包埋在环氧树脂中，在横截面和纵向平面中进行切片，抛光，蚀刻并涂上金钯，以进行扫描电子显微镜（SEM）观察。 SEM图像显示，在古猿，角鲨齿和Prosqualodon（异种齿和非多齿/有限多齿齿类群）中，内釉质组织为Hunter-Schreger带（HSB），外层为放射状釉质。这是大多数大型哺乳动物的常见模式，被认为是与食品加工和抗裂性有关的生物力学适应。化石Otekaikea sp。蝶形和多齿类分别是多齿和均齿，结构更简单，内部有径向和外部无棱釉质。径向珐琅被认为具有更高的耐磨性，并保留在几个哺乳动物的类群中，在这些类群中，相对的牙齿表面彼此滑动。这些观察结果表明，从古细菌和早期齿形目中的异齿齿和非齿形/有限齿形齿状过渡到冠状齿形齿中的齿齿和齿形齿的过渡，也与釉质Schmelzmuster的显着简化有关。这些模式可能反映了食品加工过程中的功能转变，从古细菌和早期的齿形目动物的剪切和咀嚼转变为冠状齿形动物的刺穿和咬合，这意味着大多数现存的齿形动物对饲料生物力学的要求降低。

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