|A tarsier: your distant cousin and fellow Haplorhine.|
In an article on early view in AJPA Dan Gebo takes up the issue of vertical clinging and leaping (VCL) as it relates to the ancestral pattern of primate locomotion. The term VCL refers to a uniquely primate way of getting around by clinging to vertical supports and then using hindlimbs to propel the body from one support to another.
A classic paper by Napier and Walker (1967) argued that galagos, tarsiers, and some lemurs share the behavioral traits described above, in addition to related anatomical similarities. For example, these primates have short arms that aren't very useful on the ground as well as other more detailed resemblances. These similarities, they argued, suggested that the ancestral primate must have moved around by means of VCL. Lots of people didn't buy this (reviewed in Anemone, 1990). Folks argued that Napier and Walker gave short shrift to the considerable variation in supposed VCLers. Gebo's main thrust in this new paper is the decoupling of vertical clinging on the one hand, and leaping on the other hand (puns are unintended). He argues that the ancestor of haplorhines and strepsirrhines was at least an occasional leaper, possibly cheirogaleid-like, a characterization that many others have made. Subsequently, Gebo argues, various groups of primates evolved further adaptations for leaping and specializations for vertical support use at different times, and probably for different ecological reasons.