Data from: Evolution of jaw disparity in fishes

The morphology of the vertebrate lower jaw has been used to infer feeding ecology.; transformations in mandibular shape and structure likely to have facilitated the emergence of different feeding behaviours in vertebrate evolution. Here we present elliptical Fourier shape and principal component analyses, characterizing and comparing the disparity of jaw shape in early gnathostomes and their modern primitively aquatic counterparts. 83% of shape variation is summarized on the first three principal component axes and all component clades of early gnathostomes exhibit overlapping morphological variation. Non-tetrapodomorph Palaeozoic sarcopterygians are more disparate than their extant counterparts whereas extant chondrichthyans are more disparate than their Palaeozoic counterparts. More generally, extant jawed fishes are more disparate than their Palaeozoic relatives largely because of the extensive shape variation exhibited by mandibles of extant actinopterygians. Only some areas of shape space vacated by Palaeozoic gnathostomes have been convergently refilled by living taxa. Characterization of theoretical jaw morphologies demonstrates that less than half of all possible shapes are realised by the jawed fishes that comprise our empirical dataset; many of these morphologies are realised by unrepresented terrestrial tetrapods, implying environmental constraint. Our results are incompatible with the early burst model of clade evolution and contradict the hypothesis that maximum disparity is reached early in the evolutionary history of jawed fishes.

脊椎动物下颌的形态特征长期被用于推断其摄食生态。下颌形态与结构的演化改变，大概率推动了脊椎动物演化历程中各类摄食行为的出现。本研究采用椭圆傅里叶形态分析（Elliptical Fourier Shape Analysis）与主成分分析（Principal Component Analysis），对早期有颌类（gnathostomes）及其现生原始水生类群的下颌形态差异度进行表征与比较。前三个主成分轴即可涵盖83%的形态变异，且早期有颌类的所有支系类群均表现出重叠的形态变异区间。非四足形类的古生代肉鳍鱼类（sarcopterygians）的形态差异度高于其现生类群，而现生软骨鱼类（chondrichthyans）的形态差异度则高于其古生代类群。总体而言，现生有颌鱼类的形态差异度高于其古生代近亲，这主要归因于现生辐鳍鱼类（actinopterygians）下颌所展现出的广泛形态变异。古生代有颌类所空出的形态空间区域，仅有一部分被现生类群通过趋同演化重新占据。对理论下颌形态的表征分析显示，构成本研究实证数据集的有颌鱼类仅实现了不到一半的潜在形态；而诸多未被本研究涵盖的陆生四足类则占据了其余部分形态，这暗示了环境约束的作用。本研究结果与支系演化的‘早期爆发’模型相悖，同时也驳斥了‘有颌鱼类的形态差异度峰值出现在演化早期’这一假说。