The origin of conodonts and of vertebrate mineralized skeletons
The origin of conodonts and of vertebrate mineralized skeletons
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DOI：
10.1038/nature12645
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发表时间：
2013-10-24
期刊：
影响因子：
64.8
通讯作者：
Donoghue, Philip C. J.
中科院分区：
文献类型：
--
作者：
Murdock, Duncan J. E.;Dong, Xi-Ping;Donoghue, Philip C. J.
牙形刺是一种已灭绝的无颌脊椎动物，其齿状元件是脊椎动物谱系中最早的矿化骨骼实例（1，2），激发了“由内而外”的假说，即牙齿独立于脊椎动物的真皮骨骼进化，并且在颌骨起源之前（3-6）。然而，这些主张是基于衍生真牙形石的证据。在这里，我们使用同步辐射X射线断层扫描显微镜来表征和比较形态相似的真牙形石和副牙形石元素的微观结构，以检验真牙形石（7-11）的副牙形石祖先的假设。副牙形刺表现出一系列级别的结构分化，包括真牙形刺基体常见的组织和生长模式。副牙形石的结构分化表现出不同程度的逐步收购的真牙形石字符，解决这两个群体之间的关系的争论。这意味着，真牙形石齿冠组织和脊椎动物牙釉质的假定同源性必须被拒绝，因为这些组织已经独立和收敛地进化。因此，牙形石分子和脊椎动物牙形石之间在个体发育、结构和拓扑学上的精确相似性似乎是一个显著的趋同实例。牙形刺和有颌脊椎动物的最后共同祖先可能缺乏矿化的骨骼组织。牙齿在颌骨之前进化的假设和牙齿进化的由内而外的假设必须被拒绝;牙齿似乎是在颌骨起源后不久通过牙源性能力从外部真皮向内部上皮的延伸而进化的。
Conodonts are an extinct group of jawless vertebrates whose toothlike elements are the earliest instance of a mineralized skeleton in the vertebrate lineage(1,2), inspiring the 'inside-out' hypothesis that teeth evolved independently of the vertebrate dermal skeleton and before the origin of jaws(3-6). However, these propositions have been based on evidence from derived euconodonts. Here we test hypotheses of a paraconodont ancestry of euconodonts(7-11) using synchrotron radiation X-ray tomographic microscopy to characterize and compare the microstructure of morphologically similar euconodont and paraconodont elements. Paraconodonts exhibit a range of grades of structural differentiation, including tissues and a pattern of growth common to euconodont basal bodies. The different grades of structural differentiation exhibited by paraconodonts demonstrate the stepwise acquisition of euconodont characters, resolving debate over the relationship between these two groups. By implication, the putative homology of euconodont crown tissue and vertebrate enamel must be rejected as these tissues have evolved independently and convergently. Thus, the precise ontogenetic, structural and topological similarities between conodont elements and vertebrate odontodes appear to be a remarkable instance of convergence. The last common ancestor of conodonts and jawed vertebrates probably lacked mineralized skeletal tissues. The hypothesis that teeth evolved before jaws and the inside-out hypothesis of dental evolution must be rejected; teeth seem to have evolved through the extension of odontogenic competence from the external dermis to internal epithelium soon after the origin of jaws.