Meeting Abstract

P3.59  Saturday, Jan. 5  Hind foot reversal in arboreal squirrels QUILTER, L.A.S.; LYONS, R.; ETNIER, S.A.*; Indiana University School of Medicine; Butler University; Butler University setnier@butler.edu

Hind foot reversal has been associated with arboreality in a broad range of organisms. Reversal is due to supination of the extended hind limb so the sole of the foot can be applied to a vertical substrate with the digits pointing upwards with respect to gravity during head first descent. This position allows the muscles and claws to resist the downward pull of gravity. Sciurids inhabit a wide variety of terrestrial and arboreal environments, although arboreality is considered the primitive trait in the family Sciuridae. In contrast, the joint movement allowing hind foot reversal is thought to be a derived trait in tree squirrels. Terrestrial sciurids may not exhibit hind foot reversal as the increased flexibility may compromise locomotor efficiency on the ground. In this study, we test the hypothesis that arboreal sciurids have increased hind foot mobility relative to terrestrial sciurids. We measured supination, pronation, dorsiflexion, and plantarflexion on salvaged specimens of Sciurus carolinensis (Gray squirrel), Sciurus niger (Fox squirrel), and Tamias striatus (Eastern chipmunk). These species range from the highly arboreal gray squirrel to the more terrestrial chipmunk. We found no significant differences in dorsiflexion and supination between any of the species, while plantarflexion differed significantly between gray and fox squirrels. Chipmunks exhibited significantly higher pronation than the other species. Our results do not support our hypothesis, as the arboreal tree squirrels and terrestrial chipmunks had similar hind foot mobility. We suggest that hind foot reversal allows chipmunks to move across a wide variety of substrates, rather than being a specific adaptation for arboreality.