KINEMATIC ANALYSIS OF THE LOCOMOTION OF THE POLAR BEAR (URSUS-MARITIMUS, PHIPPS, 1774) IN NATURAL AND EXPERIMENTAL CONDITIONS

The striking ability of the polar bear to travel on ice or frozen snow is tentatively related to different structural features involved in t he locomotor behaviour of the animal. A comparison with the brown bear shows the specific features, in gaits, leg movement and in ground con tact structures. It is suggested that these specific features constitu te a functional complex adapted to locomotion in polar environment. Du ring slow gaits, polar bear hind limbs are maximally extended. The leg s are able to resist the transfer of mass during the contralateral lim b swing phase. This results in a walk with swaying hips. The polar bea r uses transverse gallop to improve stability, whereas the brown bear uses rotary gallop. The polar bear is comfortable on slippery wet subs trate, while the brown bear is reluctant to move on it. Proximodistal alternation of pads and large zones with hair constitute the main char acteristics of the plantar and palmar soles of the polar bear. ?These features may constitute a functional specialization for the drainage o f water from the feet, the reinforcing of adhesion and an increase in the area of contact (snowshoe). The drainage is produced by two kinds of structures: the superficial network of the epidermis of the pads an d the hair between the pads. These hirsute zones absorb the liquid whi ch is drained off the pads by the animal's weight during the stance ph ase. The hairs are also present in the regions of the soles where thru sts are transmitted to the ground.