The importance of the evolutionary heritage of locomotion on flat ground in small mammals for the development of arboreality.

The earliest representatives of the mammalian stem line were small. Recent small mammals preserving their morphology possess rather similar kinematic and dynamic locomotor patterns, even if they are not closely related. For a small animal, the mechanics of locomotion on a large branch is comparable to locomotion on flat ground. Combining these informations, it seems sensible to start a discussion on the origins of arboreality with a detailed analysis of the locomotion of small mammals on flat ground. For this purpose, the kinematics of twelve species of mammals were observed using cineradiography, a "general limb" of small mammals was derived as a principle, and its interactions with the trunk were analyzed. These data form the basis for a theoretical upscaling of the motion patterns in arboreal animals, revealing that the transfer of torques between animal and branch becomes unavoidable, thus making the use of prehensile hands advantageous, which by their tendency of distal concentration of muscle masses force the need to change the basic kinematic patterns.