Body size, long bone geometry and locomotion in quadrupedal monkeys

Abstract

Gravitational forces place important constraints on skeletal design, including size-required modifications in bone shape and robusticity. The scaling of long bone cross sectional geometry (cortical areas, section moduli, moments of area variables related to strength in compression, bending and torsion) in quadrupedal monkeys corroborates the allometric predictions of a recent multifactorial biomechanical model for medium-sized terrestrial mammals. Almost all geometrical variables exhibit significantly positive allometry in a sample of anthropoid quadrupeds ranging in size from squirrel monkeys to baboons and proboscis monkeys; i. e., bone dimensions increase faster than predicted by simple geometric similarity. Despite this pervasive trend (also seen in studies on prosimians and great apes), theoretical indices of compressive and bending strength which have mass in the denominator decrease as a function of body size. It seems probable, therefore, that postural and other behavioral modifications must act together with allometric scaling to preserve structural integrity of the locomotor skeleton in monkeys of very different size. New kinematic data from primate quadrupeds spanning a wide range of body sizes would be very valuable in this context.