Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes
Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes
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DOI：
10.1038/nature11080
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发表时间：
2012-06-14
期刊：
影响因子：
64.8
通讯作者：
Coates, Michael I.
中科院分区：
文献类型：
--
作者：
Davis, Samuel P.;Finarelli, John A.;Coates, Michael I.
南极鱼是一种独特的古生代鱼类，是现代颚口动物起源的新辩论的核心：有颌脊椎动物包括软骨鱼类（鲨鱼，鳐和鼠鱼）和硬骨鱼类（硬骨鱼和四足动物）（1-6）。从布龙氏真鳕（2，7 -10）中我们可以初步了解到布龙氏真鳕的内部解剖结构，因为它仍然是唯一一个保存有大量细节的例子，其中心是一个表面上的硬骨鱼类头盖骨（1，2，7）。因此，在早期有颚类动物的发育过程中，真蜱已成为不可或缺的组成部分（1，11 -17）。在这里，我们提出了一个新的描述，产生新的外部和内部形态的细节，特别是周围和耳囊和神经颅顶内的区域。这些数据有助于一个新的重建，出乎意料地，类似于早期软骨鱼类头骨。主坐标分析的字符分类群矩阵，包括这些新的数据证实了这一印象：Chronododes是量化更接近软骨比硬骨鱼。然而，系统发育分析的地方的硬骨鱼干，作为一个很好的解决树，也恢复棘类作为干软骨和干nathostomes的一部分。因此，认为软骨特征的的头状骨代表共同的原始条件冠组gnathostomes。此外，这张越来越详细的早期有颚动物进化的照片突出了在颌骨起源之后但在生活分支分化之前脊椎动物颅骨的持续和深刻的解剖重组。
Acanthodians, an exclusively Palaeozoic group of fish, are central to a renewed debate on the origin of modern gnathostomes: jawed vertebrates comprising Chondrichthyes (sharks, rays and ratfish) and Osteichthyes (bony fishes and tetrapods)(1-6). Acanthodian internal anatomy is primarily understood from Acanthodes bronni(2,7-10) because it remains the only example preserved in substantial detail, central to which is an ostensibly osteichthyan braincase(1,2,7). For this reason, Acanthodes has become an indispensible component in early gnathostome phylogenies(1,11-17). Here we present a new description of the Acanthodes braincase, yielding new details of external and internal morphology, notably the regions surrounding and within the ear capsule and neurocranial roof. These data contribute to a new reconstruction that, unexpectedly, resembles early chondrichthyan crania. Principal coordinates analysis of a character-taxon matrix including these new data confirms this impression: Acanthodes is quantifiably closer to chondrichthyans than to osteichthyans. However, phylogenetic analysis places Acanthodes on the osteichthyan stem, as part of a well-resolved tree that also recovers acanthodians as stem chondrichthyans and stem gnathostomes. As such, perceived chondrichthyan features of the Acanthodes cranium represent shared primitive conditions for crown group gnathostomes. Moreover, this increasingly detailed picture of early gnathostome evolution highlights ongoing and profound anatomical reorganization of vertebrate crania after the origin of jaws but before the divergence of living clades.