Fin

A fin is a projecting locomotor or stabilizing structure in an aquatic vertebrate. Median fins lie near the midline, while paired fins occur laterally. Shape, position and internal support affect thrust, steering and stability, so not every fin has the same mechanical role.

An unpaired fin on the dorsal or ventral midline, including dorsal, anal and Caudal appendages.

A member of a bilateral appendage pair. Pectoral and pelvic fins have distinct positions and need not have originated simultaneously.

The proposal that developmental mechanisms first operating in median fins were redeployed in paired appendages. Shared mechanisms do not by themselves specify the anatomical precursor or migration route.

The proposal that discrete paired fins evolved through differentiation and regional restriction of an earlier continuous ventrolateral appendage field.

The proposal that paired appendages evolved through modification of branchial structures. Evidence for a pharyngeal contribution to the shoulder is distinguishable from evidence that the whole fin arose by conversion of a gill arch.

A paired more posterior fin associated with the pelvic girdle.

A paired anterior fin associated with the pectoral girdle.

A fin ray is a supporting element within a fin. Its structure differs among lineages; bony rays and cartilaginous or other supporting materials should not be assumed identical. Flexible arrangement of rays permits control of fin shape during movement.