The origin and evolution of the vertebrate skull have been topics of intense study for more than two centuries. Whereas early theories of skull origin, such as the influential vertebral theory, have been largely refuted with respect to the anterior (pre‐otic) region of the skull, the posterior (post‐otic) region is known to be derived from the anteriormost paraxial segments, i.e. the somites. Here we review the morphology and development of the occiput in both living and extinct tetrapods, taking into account revised knowledge of skull development by augmenting historical accounts with recent data. When occipital composition is evaluated relative to its position along the neural axis, and specifically to the hypoglossal nerve complex, much of the apparent interspecific variation in the location of the skull–neck boundary stabilizes in a phylogenetically informative way. Based on this criterion, three distinct conditions are identified in (i) frogs, (ii) salamanders and caecilians, and (iii) amniotes. The position of the posteriormost occipital segment relative to the hypoglossal nerve is key to understanding the evolution of the posterior limit of the skull. By using cranial foramina as osteological proxies of the hypoglossal nerve, a survey of fossil taxa reveals the amniote condition to be present at the base of Tetrapoda. This result challenges traditional theories of cranial evolution, which posit translocation of the occiput to a more posterior location in amniotes relative to lissamphibians (frogs, salamanders, caecilians), and instead supports the largely overlooked hypothesis that the reduced occiput in lissamphibians is secondarily derived. Recent advances in our understanding of the genetic basis of axial patterning and its regulation in amniotes support the hypothesis that the lissamphibian occipital form may have arisen as the product of a homeotic shift in segment fate from an amniote‐like condition.

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四足动物颅颈边界的发育与演化

两个多世纪以来，脊椎动物头骨的起源和进化一直是深入研究的主题。早期的颅骨起源理论，例如有影响力的椎体理论，已经在很大程度上驳斥了颅骨前（耳前）区域，而后（耳后）区域则是从最前的近轴区域衍生而来的。节段，即体节。在这里，我们回顾了现存和已灭绝四足动物的枕骨的形态和发育，通过用最近的数据增加历史记录，考虑到对头骨发育的修订知识。当相对于其沿神经轴的位置，特别是舌下神经复合体评估枕骨成分时，颅颈边界位置的许多明显种间变异以系统发育信息的方式稳定下来。根据这个标准，在 (i) 青蛙、(ii) 蝾螈和 caecilians 和 (iii) 羊膜动物中确定了三种不同的条件。最后枕骨段相对于舌下神经的位置是了解颅骨后缘演变的关键。通过使用颅孔作为舌下神经的骨学代理，对化石分类群的调查揭示了四足动物底部存在的羊膜状况。这一结果挑战了传统的颅骨进化理论，该理论认为羊膜动物的枕骨相对于轻生动物（青蛙，蝾螈，caecilians）更靠后，相反，它支持了一个在很大程度上被忽视的假设，即 lissamphibians 中减少的枕骨是次要的。我们对轴向模式的遗传基础及其在羊膜中的调节的理解的最新进展支持这样的假设，即 lissamphibian 枕骨形式可能是作为羊膜样条件的节段命运的同源转变的产物而出现的。