Comparative anatomy of the fin muscles of non-sarcopterygian fishes, with notes on homology and evolution.

Limited gross anatomical information about the muscles of fins, in particular those of the median fins, creates substantial gaps in the comparative anatomy, homologies, and evolution of these muscles across fishes. The scarcity of data also makes it difficult to interpret results obtained in developmental studies done in model organisms, such as zebrafish. To overcome these gaps, we provide descriptions of the configuration of all appendicular muscles of Amia, median fins of Polypterus, and the dorsal and anal fins of Lepisosteus and Chondrostei. The musculature of other species, including sharks and sturgeons, is also revised. We describe muscles that were previously overlooked, report sexual dimorphism in the muscles of the anal fin of Polypterus, and reveal muscle variations within Polypterus males. Species dissected for the present study thus represent all major non-sarcopterygian extant clades of gnathostomes, i.e. Chondrichthyes, Polypteriformes, Chondrostei, Lepisosteiformes, Amiiformes and Teleostei. Moreover, we compare our observations with the relatively few works that have provided information about muscles of at least some fins of these taxa in order to provide a broad discussion on - and detailed schemes showing - the major evolutionary patterns within the appendicular musculature of these fishes. Such discussion provides an opportunity for a more comprehensive understanding of appendicular evolution and fish evolution in particular and of gnathostome and morphological evolution in general.