The effects of substrate texture on the mechanics of quadrupedal arboreal locomotion in the gray short-tailed opossum (Monodelphis domestica).

Among small mammals, the ability to move on tree trunks, branches, and twigs is nearly ubiquitous. Performance and locomotor mechanics on arboreal substrates may be influenced by variation in the coefficient of friction between the hands/feet of the animal and the surface of the arboreal substrate. To test this, I examined speed, substrate reaction forces, and torque around the long axis of two cylindrical trackways with rough and smooth surfaces in gray short-tailed opossums (Monodelphis domestica). Speed was determined with videography, and forces and torques were measured by an instrumented section of the trackway. The opossums traveled more slowly on the smooth arboreal trackway. There was also significant interaction between limb (forelimbs, hindlimbs) and substrate texture (rough, smooth) in braking, propulsive, and laterally directed impulses. Running on the smooth trackway had the effect of reducing some between-limb (forelimb vs. hindlimb) differences. Stability on the rough trackway was probably maintained by relatively high momentum, but on the smooth trackway, the opossums used static methods (many limbs contacting the substrate, greater muscular effort, lower momentum) to remain stable and avoid toppling. Clearly, momentum and dynamics are often important biomechanical considerations for this generalized mammal. Highly arboreal animals can remain dynamically stable on a wider variety of substrate textures.