Functional Morphology of Leaping Behaviors in Galagids: Associations Between Landing Limb use and Diaphyseal Geometry

Abstract

An animals’ limb long bones must support its weight during postural and locomotor behaviors. Locomotor behaviors have been shown to result in bending and compressive loads of relatively large magnitude on the long bones. Of the several different types of locomotion so far studied with force plates and/or strain gauges (such as slow and fast quadrupedalism, leaping, suspension), leaping has been shown to result in the largest forces (e.g. Biewener et al., 1983; Biewener, 1990). Of the two phases of the leap where an animal is in contact with a support, take-off and landing, it is landing that results in the largest reaction forces: forces up to 10–15 times body weight have been shown to act on the limb skeleton at landing (Gunther, 1985; Gunther et al., 1991; Preuschoft, 1985). Bending is the most common and dangerous type of loading experienced by the limb skeleton (Biewener et al., 1983; Biewener and Taylor, 1986; Bertram and Biewener, 1988); bone is stronger in compression than it is in bending. The shape of long bone diaphyses dictate the behavior of the bone under load (Lanyon and Rubin, 1985; see also Cowin et al., 1984). The amount (area) and distribution (second moment of area) of diaphyseal cortical bone determine its compressive and bending strength, respectively (e.g. Wainwright et al., 1979). Recent research into the functional morphology of primate locomotion has demonstrated associations between diaphyseal cross-sectional geometry and locomotor patterns in galagids (Burr et al., 1982), lorises (Demes and Jungers, 1989), indriids (Jungers and Minns, 1979; Demes et al., 1991), macaques and other anthropoids (Ruff, 1987, 1988; Burr et al., 1989; see the review of Ruff and Runestad, 1992).