Meeting Abstract

89.1  Sunday, Jan. 6  Unique movements of Ursidae: kinematics of the forelimb in walking grizzly bears. SHINE, C*; MCGOWAN, C; ROBBINS, C; NELSON, L; University of Idaho, Moscow; University of Idaho, Moscow; Washington State University, Pullman; Washington State University, Pullman shin0453@vandals.uidaho.edu

Bears (family Ursidae) are large, quadrupedal, plantigrade animals and represent an unusual evolutionary branch; few animals are plantigrade and none that are the size of bears. Also unique to this group is an unusual rotation of the wrist and position of the elbow during locomotion. The cause and/or effect of this movement are as yet unknown; however, preliminary data from skeletons suggests that the wrist movement may be due to a more ancestral elbow joint structure. Specifically, the articulation surface of the olecranon is extended and curved to form an S-shape, which likely causes rotation with respect to the humerus during flexion and extension. In this study, we aimed to quantify the movement of the joints via high speed video. We recorded two adult female grizzly bears (Ursus arctos horribilis) at slow to moderate walking speeds with three high speed cameras. The videos were digitised and used to generate 3-D coordinates for points on the shoulder, elbow and foot of the left forelimb. Preliminary results show that at ground contact the lateral edge of the foot contacts first at an angle of 34.3+/-1.7 degrees, relative to the ground. The elbow is unusually adducted during stance, with a frontal plane angle of 20.1+/-5.3 relative to vertical, and the forefeet have a substantial medial deviation (67.6+/-3.7 degrees, relative to the direction of travel). Future research will include more detailed kinematics during both swing and stance coupled with ground reaction force data to establish a comprehensive understanding of the relationship between the novel elbow joint morphology and the resulting walking mechanics of bears.