Positional behavior and substrate use of Micromys minutus (Rodentia: Muridae): Insights for understanding primate origins

Several hypotheses have been proposed to explain the origins of primates, suggesting evolutionary scenarios that are usually paralleled to modern mammalian models that partly simulate the morpho-behavioral apomorphies of primates. The current study examines substrate use and positional behavior of tiny-sized Eurasian harvest mice (Micromys minutus) as living models for inferring the evolution of versatile behavior, flexible branch use and pedal grasping in early small-sized primates. Micromys exhibits a diverse locomotor repertoire composed of clambering and climbing, and uses postural modes requiring secure pedal grasping. It also makes considerable use of fine flexible substrates of various inclinations during both feeding/foraging and traveling. This profile seems to represent an intermediate step between stage 2 (Tupaia-stage) and stage 3 (Caluromys-stage) in Sargis et al.'s (2007) primate evolutionary scenario. Furthermore, our findings suggest that tiny size in itself brings a unique level of flexibility in posture and locomotion that has heretofore been underappreciated in the primate evolution literature.