FUNCTIONAL-ANATOMY OF HANDS OF FUR SEALS AND SEA LIONS

Dissections and manipulations of the hands of 14 specimens of fur seals and sea lions [Bassariscus astutus, Zalophus californianus , Callorhinus ursinus, Eumetopias jubata] and of generalized fissiped carnivores [Martes americana] were used to identify the structural modifications involved in formation of the expanded forelimb paddles characteristic of these pinnipeds. These morphological peculiarities were correlated with differences in locomotor function, both on land and in water, on the basis of previously published data, to identify modifications of structure and function which have adaptive value. Structural differences found in the manus of fur seals and sea lions include: reduction in size of the ulnar side of the carpus and a radial shift in the length-order of the digits, development of musculature in the antebrachial fascia which attaches to the caudal margin of the flipper, orientation of the radial side of the manus dorsal and radial to the rest of the hand, increased range of possible midcarpal movement and in deviational mobility at the 1st and 5th digits, attachment of forearm musculature onto radial digits and well-developed hypothenar muscles and absence of thenar muscles. Modifications in hand structure are reviewed as providing a morphological basis for employment of the hand to advantage during aquatic locomotion while maintaining thrust-producing and potentially energy-conserving capacities during movement on land. As such these differences in structure and function are viewed as adaptations to locomotion in the water and on land which are extensions of locomotor adaptations attributed to modifications of forelimb structure and function associated with the generation of massive aquatic locomotor thrust. The adaptive value of such modifications is interpreted as allowing fur seals and sea lions to swim with speed and thereby capture elusive fast-swimming prey while maintaining a level of terrestrial locomotor ability compatible with their amphibious mode of life.