Teeth and jaws The first vertebrates were jawless, much like a modern hagfish. There has been a lot of interest in how these forms transitioned to having jaws like most of their descendants, including humans. Much of our understanding of this process has focused on how the teeth are replaced relative to the jaw. Previous theories suggested that tooth growth that occurred lingually—or from inside out as in modern fishes—was a derived condition. Vaškaninová et al. vertebrates, suggesting that it may have been ancestral. Science, this issue p. 211 Lingual tooth replacement and dermal jaw bones may be ancestral for jawed vertebrates. The dentitions of extant fishes and land vertebrates vary in both pattern and type of tooth replacement. It has been argued that the common ancestral condition likely resembles the nonmarginal, radially arranged tooth files of arthrodires, an early group of armoured fishes. We used synchrotron microtomography to describe the fossil dentitions of so-called acanthothoracids, the most phylogenetically basal jawed vertebrates with teeth, belonging to the genera Radotina, Kosoraspis, and Tlamaspis (from the Early Devonian of the Czech Republic). Their dentitions differ fundamentally from those of arthrodires; they are marginal, carried by a cheekbone or a series of short dermal bones along the jaw edges, and teeth are added lingually as is the case in many chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods). We propose these characteristics as ancestral for all jawed vertebrates.

中文翻译：

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边缘牙列和多个真皮颌骨作为有颌脊椎动物的祖先条件

牙齿和颌骨 最早的脊椎动物没有颌骨，很像现代盲鳗。人们对这些形式如何转变为像它们的大多数后代（包括人类）一样拥有下巴引起了很多兴趣。我们对这个过程的大部分理解都集中在牙齿相对于颌骨的替换方式上。以前的理论表明，牙齿生长发生在舌侧——或者像现代鱼类那样由内而外——是一种衍生疾病。瓦什卡尼诺娃等人。脊椎动物，表明它可能是祖先。科学，这个问题 p。211 舌牙置换和真皮颌骨可能是有颌脊椎动物的祖先。现存鱼类和陆生脊椎动物的牙列在牙齿更换的模式和类型上各不相同。有人认为，共同祖先的状况可能类似于非边缘的，节肢动物的放射状排列的齿锉，早期的装甲鱼群。我们使用同步加速器显微断层扫描术来描述所谓的棘突酸的化石牙列，这是系统发育最基础的带牙齿的下颌脊椎动物，属于 Radotina、Kosoraspis 和 Tlamaspis（来自捷克共和国的早泥盆世）属。它们的牙列与节肢动物的牙列有着根本的不同。它们是边缘的，由颧骨或一系列沿着下颌边缘的短真皮骨支撑，牙齿在舌侧增加，就像许多软骨鱼类（软骨鱼类）和骨鱼类（硬骨鱼和四足动物）一样。我们建议将这些特征作为所有有颌脊椎动物的祖先。我们使用同步加速器显微断层扫描术来描述所谓的棘突酸的化石牙列，这是系统发育最基础的带牙齿的下颌脊椎动物，属于 Radotina、Kosoraspis 和 Tlamaspis（来自捷克共和国的早泥盆世）属。它们的牙列与节肢动物的牙列有着根本的不同。它们是边缘的，由颧骨或一系列沿着下颌边缘的短真皮骨支撑，牙齿在舌侧增加，就像许多软骨鱼类（软骨鱼类）和骨鱼类（硬骨鱼和四足动物）一样。我们建议将这些特征作为所有有颌脊椎动物的祖先。我们使用同步加速器显微断层扫描术来描述所谓的棘突酸的化石牙列，这是系统发育最基础的带牙齿的下颌脊椎动物，属于 Radotina、Kosoraspis 和 Tlamaspis（来自捷克共和国的早泥盆世）属。它们的牙列与节肢动物的牙列有着根本的不同。它们是边缘的，由颧骨或一系列沿着下颌边缘的短真皮骨支撑，牙齿在舌侧增加，就像许多软骨鱼类（软骨鱼类）和骨鱼类（硬骨鱼和四足动物）一样。我们建议将这些特征作为所有有颌脊椎动物的祖先。它们的牙列与节肢动物的牙列有着根本的不同。它们是边缘的，由颧骨或一系列沿着下颌边缘的短真皮骨支撑，牙齿在舌侧增加，就像许多软骨鱼类（软骨鱼类）和骨鱼类（硬骨鱼和四足动物）一样。我们建议将这些特征作为所有有颌脊椎动物的祖先。它们的牙列与节肢动物的牙列有着根本的不同。它们是边缘的，由颧骨或一系列沿着下颌边缘的短真皮骨支撑，牙齿在舌侧增加，就像许多软骨鱼类（软骨鱼类）和骨鱼类（硬骨鱼和四足动物）一样。我们建议将这些特征作为所有有颌脊椎动物的祖先。