Vertical clinging and leaping revisited: vertical support use as the ancestral condition of strepsirrhine primates.

A re-examination of primate foot and knee anatomy suggests that strepsirrhine primates (adapiforms and lemuriforms) possess a unique and derived hindlimb related to their use of vertical supports. In contrast, leaping adaptations are older and shared by both major euprimate clades, Strepsirrhini and Haplorhini. Combining this derived hindlimb anatomy with leaping suggests that ancestral strepsirrhines were at least frequent vertical support users and leapers, and perhaps vertical clingers and leapers. These initial strepsirrhine adaptations were preadaptive for later lemuriform vertical clingers and leapers. In contrast, haplorhine vertical clingers and leapers require additional foot and leg modifications to accommodate a vertical clinging and leaping lifestyle. The movement pattern called vertical clinging and leaping evolved independently among different primate lineages throughout primate evolutionary history for several different ecological reasons.