The fish-to-tetrapod transition is one of the most iconic events in vertebrate evolution, yet fundamental questions regarding the dynamics of this transition remain unresolved. Here, we use advances in Bayesian morphological clock modelling to reveal the evolutionary dynamics of early tetrapodomorphs (tetrapods and their closest fish relatives). We show that combining osteological and ichnological calibration data results in major shifts on the time of origin of all major groups of tetrapodomorphs (up to 25 million years) and that low rates of net diversification, not fossilization, explain long ghost lineages in the early tetrapodomorph fossil record. Further, our findings reveal extremely low rates of morphological change for most early tetrapodomorphs, indicating widespread stabilizing selection upon their ‘fish’ morphotype. This pattern was broken only by elpistostegalians (including early tetrapods), which underwent sustained high rates of morphological evolution for ~30 Myr during the deployment of the tetrapod body plan.

鱼到四足动物的转变是脊椎动物进化中最具标志性的事件之一，但有关这种转变动力学的基本问题仍未解决。在这里，我们利用贝叶斯形态时钟建模的进步来揭示早期四足动物（四足动物及其最近的鱼类亲属）的进化动态。我们表明，结合骨学和 ichnological 校准数据导致所有主要四足类动物群（长达 2500 万年）的起源时间发生重大变化，并且净多样化率低，而不是石化，解释了早期四足类动物的长鬼谱系化石记录。此外，我们的研究结果揭示了大多数早期四足动物的形态变化率极低，表明对其“鱼”形态类型的广泛稳定选择。