Polar bear paw pad surface roughness and its relevance to contact mechanics on snow.

Microscopic papillae on polar bear paw pads are considered adaptations for increased friction on ice/snow, yet this assertion is based on a single study of one species. The lack of comparative data from species that exploit different habitats renders the ecomorphological associations of papillae unclear. Here, we quantify the surface roughness of the paw pads of four species of bear over five orders of magnitude by calculating their surface roughness power spectral density.