91.4 Saturday, Jan. 7 Kinematics of terrestrial locomotion in phocid seals: Importance of spinal flexion by an amphibious mammal GARRETT, J.N.*; FISH, F.E.; West Chester Univ., Pennsylvania; West Chester Univ., Pennsylvania firstname.lastname@example.org
Pinnipeds are amphibious mammals that retain limbs to function on land and in water. The evolution of the limbs as flippers has placed constraints on the terrestrial locomotion of pinnipeds. Phocid seals cannot draw their hindlimbs under the body and must move over land by undulatory movements of the body in concert with the forelimbs. Previous examinations of terrestrial locomotion were limited to gross descriptions without consideration of terrain as an influence on performance. The purpose of this study was to detail the kinematics of terrestrial locomotion of phocid seals. For video analysis, grey seals (Halichoerus grypus) and harbor seals (Phoca vitulina) were recorded in captivity on level ground and in the wild on rocky beaches. Grey and harbor seals exhibited dorsoventral undulations with the sternum and pubis serving as the main weight bearing points. Forward movement was accomplished in an inchworm manner by a combination of spinal flexion and foreflipper protraction. An anteriorly directed wave of flexion by the spine positioned the foreflippers, which served as a pivot and aided in lifting the sternum off the ground. The foreflippers were retracted to pull the body forward. In some cases, the foreflippers were not used and forward progression was accomplished solely by spinal flexion. The seals traveled across a level platform with and without the use of the foreflippers. The seals could move on land at about 0.4 m/s. The amplitude of the spine decreased with increasing speed while the frequency of the undulatory wave in the body increased. This reliance on spinal flexion with reduced participation of the limbs incurs reduced performance for movement on land as aquatic locomotion is enhanced in phocids.