A primitive placoderm sheds light on the origin of the jawed vertebrate face
A primitive placoderm sheds light on the origin of the jawed vertebrate face
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DOI：
10.1038/nature12980
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发表时间：
2014-03-27
期刊：
影响因子：
64.8
通讯作者：
Ahlberg, Per E.
中科院分区：
文献类型：
--
作者：
Dupret, Vincent;Sanchez, Sophie;Ahlberg, Per E.
现存的脊椎动物形成两个分支，无颚的圆口动物（七鳃鳗和盲鳗）和有颚的颚口动物（所有其他脊椎动物），具有对比鲜明的面部结构（1，2）。这些在发育过程中出现，只是因为颅原基生长模式的几个关键差异：值得注意的是，鼻囊和垂体起源于圆口动物的单个基板，但在有颌动物中起源于单独的基板，并且在圆口动物中，视下外生间充质向前迁移到单个基板的两侧，但在有颌动物中，则迁移到基板之间（3-8）。化石茎有颌动物保存了丰富的颅骨解剖结构，这些解剖结构为发育过程提供了替代物，并允许从无颌脊椎动物到有颌脊椎动物的过渡被分解为进化步骤（7，9 -12）。在这里，我们使用传播相位对比同步辐射显微断层扫描成像的原始盾皮动物（有颚茎颚）Romundina（13）的颅骨解剖结构，并表明它结合了有颚脊椎动物的结构与颅骨和大脑的比例类似的圆口动物和盔形动物（无颚茎颚颚）Shuyu（11）。这种组合似乎是原始的有颌脊椎动物，并建议之间的解耦外胚间充质生长轨迹，外胚间充质增殖，和大脑的形状变化的起源颚口。
Extant vertebrates form two clades, the jawless Cyclostomata (lampreys and hagfishes) and the jawed Gnathostomata (all other vertebrates), with contrasting facial architectures(1,2). These arise during development from just a few key differences in the growth patterns of the cranial primordia: notably, the nasal sacs and hypophysis originate from a single placode in cyclostomes but from separate placodes in gnathostomes, and infraoptic ectomesenchyme migrates forward either side of the single placode in cyclostomes but between the placodes in gnathostomes(3-8). Fossil stem gnathostomes preserve cranial anatomies rich in landmarks that provide proxies for developmental processes and allow the transition from jawless to jawed vertebrates to be broken down into evolutionary steps(7,9-12). Here we use propagation phase contrast synchrotron microtomography to image the cranial anatomy of the primitive placoderm (jawed stem gnathostome) Romundina(13), and show that itcombines jawed vertebrate architecture with cranial and cerebral proportions resembling those of cyclostomes and the galeaspid (jawless stem gnathostome) Shuyu(11). This combination seems to be primitive for jawed vertebrates, and suggests a decoupling between ectomesenchymal growth trajectory, ectomesenchymal proliferation, and cerebral shape change during the origin of gnathostomes.