Early primate evolution: insights into the functional significance of grasping from motion analyses of extant mammals

Despite differences in the assumed ecological context in competing evolutionary scenarios for early primate locomotion, there appears to be consensus about the adaptive significance of grasping for the exploitation of the terminal branch habitat. I attempt to review first the phylogenetic framework of early primate evolution. Then, I focus on proposed extant analogues for potential ancestral morphotypes of early primate evolution and motion analyses conducted to gain insight specifically into the role of grasping during small-branch locomotion. Studies concerned with proposed extant analogues, such as treeshrews, didelphid marsupials, mouse lemurs, tamarins and marmosets, marsupial gliders and various small arboreal rodents, are summarized. This overview demonstrates a striking variability and plasticity of strategies to cope with the challenging functional demands of locomotion in the terminal branch habitat and helps to identify open questions for further research. For example, potential morphological correlates for specific behaviours still need to be validated in future in-depth quantitative experimental studies. Comparative approaches beyond the anatomy that specifically account for data on locomotor and postural behaviour of extant species, also including phylogenetically informed analyses, are mostly lacking and should be intended to link evolutionary patterns of morphological change with functional characteristics observed in experimental studies.