Fig. 3.

Romer's interpretation of amniote primary girdle evolution. Building on the work of Williston (1911, 1925), Romer hypothesized that the primitive coracoid of non-amniote tetrapods such as †Seymouria, the procoracoid, was retained as the coracoid of modern reptiles. Among synapsids a second element evolved, the metacoracoid. Whereas synapsids eventually lost the primitive reptilian procoracoid, the newly evolved metacoracoid was retained by therians as the coracoid process. Although this hypothesis has long been accepted, it is not supported by the data presented herein. Abbreviations: cart (epicoracoidal and suprascapula cartilages), cpr (coracoid process), met (metacoracoid), pro (procoracoid), scp (scapula). Glenoid shaded. Source for image: modified from The comparison of mammalian and reptilian coracoids, A. S. Romer (1922), ©Journal of Morphology); reprinted with permission of Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc. Not to scale.