Teeth outside the mouth? Evolution and development of the sawfish and sawshark rostral dentitions (Elasmobranchii; Chondrichthyes)
Teeth outside the mouth? Evolution and development of the sawfish and sawshark rostral dentitions (Elasmobranchii; Chondrichthyes)
复制标题
牙齿在嘴外面？
DOI：
--
复制
发表时间：
2015
期刊：
影响因子：
--
通讯作者：
Z. Johanson
中科院分区：
文献类型：
--
作者：
M. Welton;Moya M. Smith;C. Underwood;Z. Johanson
脊椎动物齿系的起源，作为一个模式，功能单位与颌骨，仍然存在争议。假设表明齿系从外部盾鳞进化而来，或者从口咽腔内的齿冠进化而来，没有来自外部真皮结构的输入。后一种假说认为，口腔齿系和鳞片来自不同的发展系统，而前者认为他们有一个共同的发展系统。后一种假说意味着口腔齿系局限于口腔内，而前一种假说意味着皮肤结构异位迁移到口腔内。为了验证这些假设，我们研究了细长的喙（“锯”）和相关的口腔齿系在三个chondrichthyan组：Pristiophoridae（Selachii），Pristidae（Batoidea）和化石Sclerorhynchoidea（Batoidea）。成人和胚胎个体的喙锯进行了研究，通过3D渲染，体积密度模型，从X射线计算机断层扫描，揭示数据的地形位置，系列大小差异，生长阶段，逐步矿化，时间和模式的牙齿样结构的替代，所有共同定位与矿化海湾的棱柱喙软骨。我们认为，这些结构缺乏口腔齿系的图案和更换特性，而是代表真皮衍生的neomorphic结构上的喙修改从板状鳞片，独立的口腔牙齿。
Origins of the vertebrate dentition, as a patterned, functional unit associated with the jaws, remain contentious. Hypotheses suggest dentitions evolved from external placoid scales, or alternatively, from denticles within the oropharyngeal cavity, with no input from external dermal structures. The latter hypothesis suggests that oral dentitions and scales derive from separate developmental systems, while the former suggests they share a common developmental system. The latter hypothesis implies that oral dentitions are restricted to the oropharygeal cavity, while the former implies heterotopic migration of dermal structures into the mouth. To test these hypotheses, we examined the elongate rostrum (‘saw’) and associated oral dentitions in three chondrichthyan groups: Pristiophoridae (Selachii), Pristidae (Batoidea) and the fossil Sclerorhynchoidea (Batoidea). The rostrum saw of adult and embryonic individuals was investigated via 3D-rendered, volume density models from x-ray computed tomography, revealing data on topographic position, series size differences, growth stages, progressive mineralization, timing and mode of replacement of the tooth-like structures, all co-located with mineralized embayments of prismatic rostral cartilage. We suggest these structures lack the patterning and replacement characteristic of oral dentitions and instead represent dermally-derived neomorphic structures on the rostrum modified from placoid scales, independent of oral teeth.