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 the locomotor behaviour of the animal. A comparison with the brown bear shows the specific features, in gaits, leg movement and in ground contact structures. It is suggested that these specific features constitute a functional complex adapted to locomotion in polar environment. During slow gaits, polar bear hind limbs are maximally extended. The legs are able to resist the transfer of mass during the contralateral limb swing phase. This results in a walk with swaying hips. The polar bear uses transverse gallop to improve stability, whereas the brown bear uses rotary gallop. The polar bear is comfortable on slippery wet substrate, while the brown bear is reluctant to move on it. Proximodistal alternation of pads and large zones with hair constitute the main characteristics of the plantar and palmar soles of the polar bear. ?These features may constitute a functional specialization for the drainage of 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 and the hair between the pads. These hirsute zones absorb the liquid which is drained off the pads by the animal's weight during the stance phase. The hairs are also present in the regions of the soles where thrusts are transmitted to the ground.