BACKGROUND Tooth morphology within theropod dinosaurs has been extensively investigated and shows high disparity throughout the Cretaceous. Changes or diversification in feeding ecology, i.e., adoption of an herbivorous diet (e.g., granivorous), is proposed as a major driver of tooth evolution in Paraves (e.g., Microraptor, troodontids and avialans). Here, we studied the microscopic features of paravian non-avian theropod and avialan teeth using high-spatial-resolution synchrotron transmission X-ray microscopy and scanning electron microscopy. RESULTS We show that avialan teeth are characterized by the presence of simple enamel structures and a lack of porous mantle dentin between the enamel and orthodentin. Reduced internal structures of teeth took place independently in Early Cretaceous birds and a Microraptor specimen, implying that shifts in diet in avialans from that of closely related dinosaurs may correlate with a shift in feeding ecology during the transition from non-avian dinosaurs to birds. CONCLUSION Different lines of evidence all suggest a large reduction in biting force affecting the evolution of teeth in the dinosaur-bird transition. Changes in teeth microstructure and associated dietary shift may have contributed to the early evolutionary success of stemward birds in the shadow of other non-avian theropods.

中文翻译：

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牙齿的超微结构减少：从非禽类恐龙到鸟类的饮食过渡的意义。

背景技术兽脚类恐龙内的牙齿形态已被广泛研究，并在整个白垩纪显示出高度差异。饲料生态的变化或多样化，即​​采用草食（例如肉食），被认为是帕拉韦斯（例如微型猛禽，齿形齿和鸟粪）牙齿进化的主要驱动力。在这里，我们使用高空间分辨率同步加速器透射X射线显微镜和扫描电子显微镜研究了巴拉圭非禽兽脚类动物和阿凡兰齿的微观特征。结果我们显示，普通牙的特征是牙釉质结构简单，牙釉质与原牙之间缺乏多孔的牙本质牙本质。早白垩世鸟类和微型猛禽标本中牙齿内部结构的减少是独立发生的，这表明从非相关恐龙到鸟类的过渡过程中，鸟类的饮食结构从密切相关的恐龙的变化可能与喂养生态的变化有关。结论不同的证据都表明，咬合力的大幅度降低会影响恐龙-鸟类过渡时期牙齿的进化。牙齿微结构的变化和相关的饮食变化可能在其他非禽类兽脚亚目动物的阴影下，促进了成年鸟类的早期进化成功。