Comparative Anatomy of Pectoral Girdle and Pectoral Fin in Russian Sturgeon and American Paddlefish

Acipenseriformes occupy an important place in the evolutionary history. Skeleton of their pectoral fins has elements related to teleosts, but also to tetrapods. This article summarises and compares anatomical structure of the pectoral girdle and pectoral fin of Russian sturgeon (Acipenser gueldenstaedtii) and American paddlefish (Polyodon spathula). These species possess pectoral fins with some distinctive features in their structure. The pectoral girdles are composed of both cartilaginous and ossified elements. Unlike sturgeons, American paddlefish does not have an interclavicle and suprascapular cartilage. Moreover, its cleithrum doesn't form medially directed lamina. The quantity of the proximal radials in the investigated fish species are not the same. The dorsal and ventral muscles, which act on the pectoral fin of Russian sturgeon and American paddlefish, are not equally developed. In our opinion, this is caused by the differences in the mode of life, motility of fins, as well as by stabilisation of body during swimming.