Does the muscular anatomy of the pelvic fin of the extant coelacanth Latimeria chalumnae (Actinistia: Latimeriidae) provide information on its mobility and role during locomotion?
Résumé
Cœlacanths are sarcopterygian fishes that were originally known only from their fossil record and assumed extinct since the Upper Cretaceous (70My ago). The discovery of a living coelacanth, Latimeria chalumnae, offshore South Africa in 1938, was a surprise for the scientific community, and provide a unique opportunity to study the anatomy of this close relative to tetrapods. Its paired fins are of special interest because of their mono-basal articulation and their proximal endoskeleton, homologous to that of tetrapods. A recent study on the functional anatomy of the musculature of the pectoral fin showed that it is more complex than previously thought. Here, we focus on the pelvic fin and hypothesize that the muscles are equally complex and allow complex movements of the fins. A detailed dissection and anatomical description of the pelvic fins was undertaken on an adult specimen of L. chalumnae preserved in the MNHN collections, Paris. According to previous descriptions, the pelvic fin musculature presents a three-layered organization: the adductor and abductor muscles form the superficial and middle layers, whereas the pronator and supinator form the deep layer. Amongst others, our preliminary results show that the muscle bundles of the superficial and middle layers lead to adduction or abduction movements, but also to the protraction or retraction of the fin. Moreover, whereas previous studies documented about twenty muscles, we observed and described more than 70 clearly individualized muscle bundles. This complex organization of the muscle bundles is congruent with a high mobility of the pelvic fin as quantified based on in-vivo video recording.