Mammals and reptiles have evolved divergent adaptations for processing abrasive foods. Mammals have occluding, diphyodont dentitions with taller teeth (hypsodonty), more complex occlusal surfaces, continuous tooth eruption, and forms of prismatic enamel that prolong the functional life of each tooth [1, 2]. The evolution of prismatic enamel in particular was a key innovation that made individual teeth more resilient to abrasion in early mammals [2-4]. In contrast, reptiles typically have thin, non-prismatic enamel, and shearing, polyphyodont dentitions with multi-cusped or serrated tooth crowns, multiple tooth rows, rapid tooth replacement rates, or batteries made of hundreds of teeth [5-9]. However, there are rare cases where reptiles have evolved alternative solutions to cope with abrasive diets. Here, we show that the combined effects of herbivory and an ancestral loss of tooth replacement in a lineage of extinct herbivorous sphenodontians, distant relatives of the modern tuatara (Sphenodon punctatus) [10], are associated with the evolution of wear-resistant and highly complex teeth. Priosphenodon avelasi, an extinct sphenodontian from the Cretaceous of Argentina, possesses a unique cone-in-cone dentition with overlapping generations of teeth forming a densely packed tooth file. Each tooth is anchored to its predecessor via a rearrangement of dental tissues that results in a novel enamel-to-bone tooth attachment. Furthermore, the compound occlusal surfaces, thickened enamel, and the first report of prismatic enamel in a sphenodontian are convergent strategies with those in some mammals, challenging the perceived simplicity of acrodont dentitions [11-15] and showcasing the reptilian capacity to produce complex and unusual dentitions.

中文翻译：

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阿根廷晚白垩世 Sphenodontians 独特的牙齿形态和棱形釉质。

哺乳动物和爬行动物已经进化出不同的适应性来处理磨蚀性食物。哺乳动物具有咬合的双牙列牙列，具有较高的牙齿 (hypsodonty)、更复杂的咬合面、连续的牙齿萌出以及延长每颗牙齿功能寿命的棱柱形牙釉质 [1, 2]。特别是棱柱形牙釉质的进化是一项关键创新，它使早期哺乳动物的单个牙齿更能抵抗磨损[2-4]。相比之下，爬行动物通常具有薄的非棱柱形牙釉质和剪切多齿牙列，具有多尖牙或锯齿状牙冠、多排牙、快速的牙齿更换率或由数百颗牙齿组成的电池 [5-9]。然而，在极少数情况下，爬行动物已经进化出替代解决方案来应对磨蚀性饮食。这里，我们表明，在已灭绝的草食性蝶齿类动物（现代大蜥蜴（Sphenodon punctatus）的远亲）[10] 的谱系中，食草性和祖先牙齿更换的综合影响与耐磨和高度复杂的牙齿的进化有关. Priosphenodon avelasi 是一种来自阿根廷白垩纪的已灭绝的蝶齿类动物，拥有独特的锥形牙列，具有重叠的几代牙齿，形成密集的牙锉。每颗牙齿都通过牙齿组织的重新排列固定在其前身上，从而形成一种新型的牙釉质与骨骼的牙齿附着物。此外，复合咬合面、增厚的牙釉质和首次报道的楔形牙釉质是与某些哺乳动物的趋同策略，