Early terrestrial vertebrates (amniotes) provide a classic example of diversification following adaptive zone invasion. The initial terrestrialization of vertebrates was closely followed by dietary diversification, as evidenced by a proliferation of craniomandibular and dental adaptations. However, morphological evolution of early amniotes has received limited study, in analyses with restricted taxonomic scope, leaving substantial questions about the dynamics of this important terrestrial radiation. We use novel analyses of discrete characters to quantify variation in evolutionary rates and constraints during diversification of the amniote feeding apparatus. We find evidence for an early burst, comprising high rates of anatomical change that decelerated through time, giving way to a background of saturated morphological evolution. Subsequent expansions of phenotypic diversity were not associated with increased evolutionary rates. Instead, variation in the mode of evolution became important, with groups representing independent origins of herbivory evolving distinctive, group-specific morphologies and thereby exploring novel character-state spaces. Our findings indicate the importance of plant–animal interactions in structuring the earliest radiation of amniotes and demonstrate the importance of variation in modes of phenotypic divergence during a major evolutionary radiation.

早期陆生脊椎动物（羊膜动物）提供了适应区入侵后多样化的典型例子。脊椎动物最初的陆生化紧随其后的是饮食多样化，颅颌骨和牙齿适应性的增殖就证明了这一点。然而，早期羊膜动物的形态进化在有限的分类学范围内得到了有限的研究，对这种重要的陆地辐射的动力学留下了实质性的疑问。我们使用对离散特征的新颖分析来量化羊膜动物喂养装置多样化过程中进化率和约束的变化。我们找到了早期爆发的证据，包括随着时间的推移减速的高速率解剖变化，让位于饱和形态进化的背景。随后表型多样性的扩展与进化率的增加无关。相反，进化模式的变化变得很重要，代表食草动物独立起源的群体进化出独特的、特定于群体的形态，从而探索新的特征-状态空间。我们的研究结果表明植物-动物相互作用在构建最早的羊膜动物辐射中的重要性，并证明了在主要进化辐射期间表型分化模式变异的重要性。组特定的形态，从而探索新的字符状态空间。我们的研究结果表明植物-动物相互作用在构建最早的羊膜动物辐射中的重要性，并证明了在主要进化辐射期间表型分化模式变异的重要性。组特定的形态，从而探索新的字符状态空间。我们的研究结果表明植物-动物相互作用在构建最早的羊膜动物辐射中的重要性，并证明了在主要进化辐射期间表型分化模式变异的重要性。