Pedal grasping in an arboreal rodent relates to above-branch behavior on slender substrates

In order to exploit the three-dimensional, discontinuous and unstable arboreal milieu, most arboreal mammals employ efficient foot (pedal) grasping that establishes firm contact with the substrate and enables secure and safe locomotion and postures. Such pedal grasp can be performed in variable ways in relation to substrate characteristics. In order to investigate the interplay between pedal grasping modes, arboreal locomotor and postural behavior, and substrate size and inclination in arboreal mammals, we filmed and quantitatively analyzed these behaviors in captive African woodland dormice. Our observations revealed that African woodland dormice exhibited a flexible locomotor and postural repertoire, mainly on small and horizontal substrates. Hallucal grasping was the main pedal grasping mode and associated with walk, clamber and stand on mainly small-to medium-sized horizontal substrates, whereas claws were commonly used during vertical climb and cling on medium-sized to large vertical substrates. These results clearly demonstrate the importance of hallucal grasping for balancing above, and not below, small-and medium-sized arboreal substrates of moderate inclinations. Therefore, we assert that efficient pedal grasping and its associated positional behavior may have been fundamental for the differentiation and successful radiation of virtually all early mammals that sought refuge in tree canopies, enabling efficient utilization of the small branch niche. Evidence suggests that extant arboreal rodents offer useful functional morphology evidence of the transitional stages that lead to arboreal specialists, euprimates included, and research toward this direction has much to offer to our understanding of evolutionary adaptations exhibited by small-bodied arboreal mammals.