MORPHOLOGICAL CONSERVATION OF LIMB NATURAL PENDULAR PERIOD IN THE DOMESTIC DOG (CANIS-FAMILIARIS) - IMPLICATIONS FOR LOCOMOTOR ENERGETICS

For better understanding of the links between limb morphology and the metabolic cost of locomotion, we have characterized the relationships between limb length and shape and other functionally important variabl es in the straightened forelimbs and hindlimbs of a sample of 12 domes tic dogs (Canis familiaris). Intra-animal comparisons show that foreli mbs and hindlimbs are very similar (not significantly different) in na tural pendular period (NPP), center-of-mass, and radius of gyration, e ven though they differ distinctly in mass, length, moment-of-inertia, and other limb proportions. The conservation of limb NPP, despite pron ounced dissimilarity in other limb characteristics, appears to be the result of systematic differences in shape, forelimbs tending to be cyl indrical and hindlimbs conical. Estimating limb NPP for other species from data in the literature on segment inertia and total limb length, we present evidence that the similarity between forelimbs and hindlimb s in NPP is generally true for mammals across a large size range. Limb s swinging with or near their natural pendular periods will maximize w ithin-limb pendular exchange of potential and kinetic energy. As all f our limbs of moderate-and large-size animals swing with the same perio d during walking, maximal advantage can be derived from the pendular e xchange of energy only if forelimbs and hindlimbs are very similar in NPP. We hypothesize that an important constraint in the evolution of l imb length and shape is the locomotor economy derived from forelimbs a nd hindlimbs of similar natural pendular period. (C) 1997 Wiley-Liss, Inc.