The mammalian neck adopts a variety of postures during daily life and generates numerous head trajectories. Despite its functional diversity, the neck is constrained to seven cervical vertebrae in (almost) all mammals. Given this low number, an unexpectedly high degree of modularity of the mammalian neck has more recently been uncovered. This work aims to review neck modularity in mammals from a developmental, morpho-functional, and paleontological perspective and how high functional diversity evolved in the mammalian neck after the occurrence of meristic limitations. The fixed number of cervical vertebrae and the developmental modularity of the mammalian neck are closely linked to anterior Hox genes expression and strong developmental integration between the neck and other body regions. In addition, basic neck biomechanics promote morpho-functional modularity due to preferred motion axes in the cranio-cervical and cervico-thoracic junction. These developmental and biomechanical determinants result in the characteristic and highly conserved shape variation among the vertebrae that delimits morphological modules. The step-wise acquisition of these unique cervical traits can be traced in the fossil record. The increasing functional specialization of neck modules, however, did not evolve all at once but started much earlier in the upper than in the lower neck. Overall, the strongly conserved modularity in the mammalian neck represents an evolutionary trade-off between the meristic constraints and functional diversity. Although a morpho-functional partition of the neck is common among amniotes, the degree of modularity and the way neck disparity is realized is unique in mammals.

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从发育、形态功能和古生物学角度看哺乳动物颈部的进化

哺乳动物的颈部在日常生活中采用多种姿势并产生许多头部轨迹。尽管其功能多样，但（几乎）所有哺乳动物的颈部都被限制在七块颈椎骨上。鉴于这个低数量，最近发现了哺乳动物颈部出乎意料的高度模块化。这项工作旨在从发育、形态功能和古生物学的角度回顾哺乳动物的颈部模块化，以及在发生分生限制后哺乳动物颈部的高度功能多样性是如何进化的。颈椎的固定数量和哺乳动物颈部的发育模块与前部 Hox 基因表达以及颈部与其他身体区域之间的强烈发育整合密切相关。此外，由于颅颈和颈胸交界处的首选运动轴，基本的颈部生物力学促进了形态功能模块化。这些发育和生物力学决定因素导致限定形态模块的椎骨之间的特征性和高度保守的形状变异。这些独特的宫颈特征的逐步获得可以在化石记录中进行追踪。然而，颈部模块功能的日益专业化并不是一下子发展起来的，而是在上颈部比下颈部更早开始。总的来说，哺乳动物颈部高度保守的模块性代表了分生限制和功能多样性之间的进化权衡。虽然颈部的形态功能分区在羊膜动物中很常见，