Two main theories have been used to explain the origin of pectoral and pelvic appendages. The “fin‐fold theory” proposes that they evolved from a trunk bilateral fin fold, while Gegenbaur's theory assumes they derived from the head branchial arches. However, none of these theories has been fully supported. The “fin‐fold” theory is mainly often accepted due to some existing developmental data, but recent developmental studies have revived Gegenbaur's theory by revealing common mechanisms underlying the patterning of branchial arches and paired appendages. Here I review developmental data and many others lines of evidence, which lead to a crucial question: might the apparent contradictions between the two theories be explained by a dual origin of the pectoral appendage, that is, the pectoral girdle and fin/limb being mainly related to the head and trunk, respectively? If this is so then (a) the pectoral and pelvic girdles would not be serial homologues; (b) the term “developmental serial homologues” could only potentially be applied to the pectoral and pelvic fins/limbs. Fascinatingly, in a way this would be similar to what Owen had already suggested, more than 170 years ago: that the pectoral and pelvic girdles are mainly related to the head and trunk, respectively.

中文翻译：

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Cranial or postcranial-脊椎动物胸附件的双重起源结合鳍褶和鳃弓理论？

两种主要的理论已被用来解释胸骨和骨盆附属物的起源。“鳍褶理论”认为它们是从躯干双侧鳍褶演化而来，而 Gegenbaur 的理论则假设它们源自头部鳃弓。然而，这些理论都没有得到完全支持。“鳍褶”理论主要由于一些现有的发育数据而被普遍接受，但最近的发育研究通过揭示鳃弓和成对附属物形成模式的共同机制，复兴了 Gegenbaur 的理论。在这里，我回顾了发育数据和许多其他证据，它们引出了一个关键问题：两种理论之间明显的矛盾是否可以用胸附件的双重起源来解释，即，胸带和鳍/四肢分别与头部和躯干有关吗？如果是这样，那么 (a) 胸带和骨盆带将不是系列同源物；(b) 术语“发育系列同源物”可能仅适用于胸鳍和骨盆鳍/四肢。令人着迷的是，这在某种程度上类似于欧文在 170 多年前已经提出的建议：胸带和骨盆带主要分别与头部和躯干有关。