LONG-BONE CROSS-SECTIONAL DIMENSIONS, LOCOMOTOR ADAPTATIONS AND BODY-SIZE IN PROSIMIAN PRIMATES

The cross-sectional geometry of primate long bones appears to be closely related to body size and locomotor behavior. This study investigates this aspect of skeletal design in the humerus and femur of living prosimian primates, a group characterized by a diversity of locomotor modes and a wide range of body sizes. The geometrical variables were collected from biplanar radiographs using formulae for hollow ellipses to approximate cortical area, wall thickness, second and polar moments of area, and section modulus. Indices of strength in static compression and bending were also derived from these data, limb length and body mass. For prosimians as a group, all cross-sectional geometrical properties scale in a positive allometric fashion with body mass (although some of the humeral values have confidence limits that include isometry). Despite positive allometry, measures of strength in static loading decrease as a function of body size and imply that alterations in body posture and locomotion are necessary in order to maintain stress/strain similarity. Within prosimians, leapers tend to have more robust femora (with elongated anteroposterior axes) than non-saltatory species of the same size; no such distinctions exist for the humerus (but Daubentonia exhibits an unusually strong humerus). Slow climbing lorisines, although exposed to only moderate locomotor forces, are not at the low end of absolute and relative bone strength variation. Prosimians less than 1-2 kg exhibit considerable variation in cross-sectional geometry, a finding that could complicate attempts to use such data to reconstruct body size in small-bodied fossil prosimians. Measures of wall thickness (K-values) appear to be of limited utility in the functional analysis of skeletal design in extant prosimians. Compound indices of relative strength-although useful in functional allometric analyses - do not reliably differentiate among either locomotor or taxonomic groups. Functional differences among taxa are more obvious in geometrical properties when body size is used as a covariate. © 1993 Academic Press. All rights reserved.