ABSTRACT
Most studies on the origin of limbs focus on fossil skeletal structures, mainly because fossils usually do not preserve soft tissues, and because it is difficult to compare fish fins and tetrapod limbs as they are morphologically very different. This chapter proposes that the fish abductor superficialis gave rise to and is homologous with all of the developmentally ventral superficial muscles. It also proposes that the second most superficial ventral muscle of the pectoral fin is homologous with the second most superficial ventral pectoral muscle of salamanders, developmentally. The chapter provides a detailed list of topological correspondences between all pectoral vs. pelvic appendicular muscles, including girdle/stylopodial muscles, based on the same empirical comparative, evolutionary, and developmental data used for the homology hypotheses. Accordingly, extant phylogenetic bracketing, one of the most powerful tools for soft tissue reconstruction, has never been used to study the fin–limb transition, despite the fact that the relationships of extant sarcopterygians have long been well established.
