Coelacanths illuminate deep-time evolution of cranial musculature in jawed vertebrates

Coelacanths are rare fishes that occupy a key evolutionary position in the vertebrate tree of life. Despite being exhaustively studied, we found that a substantial part of the knowledge on their cranial musculature was mistaken. Eleven previously reported coelacanth "muscles" are nonexistent, while three previously unknown muscle subdivisions and connections are found. These findings markedly affect our understanding of the deep-time cranial evolution of jawed vertebrates (gnathostomes). Only 13% of the previously identified myological evolutionary novelties for the major gnathostome lineages proved to be accurate, but several new ones are proposed. We show that low, moderate, and high levels of cranial muscle innovation characterized the emergence of lobe-finned (sarcopterygian), cartilaginous (chondrichthyan), and ray-finned (actinopterygian) fishes, respectively. The novelties in the latter group resulted in the evolution of a second active mechanism for the expansion of the oropharyngeal cavity, which was probably crucial for the predominance of suction feeding versus bite feeding in extant actinopterygians.