Allometry and Habitat-Related Adaptations in the Postcranial Skeleton of Cervidae

Scott, Kathleen

Interspecific variation in the limb dimensions of Cervidae can be separated into two major categories: regular allometric changes correlated with increasing size, and deviations from regular scaling related to particular habitats or locomotor styles. Most dimensions of the skeleton are highly correlated with body weight. Lengths of radius, metacarpal, tibia, and metatarsal have the lowest R-square values. Limb lengths generally scale against body weight with negative allometry, diameters and areas with positive allometry. Exponents for most relationships of forelimb bones are higher than those of the hindlimb; that is, as body weight increases forelimb bones decrease in length more slowly and increase in thickness more rapidly than do hindlimb bones. Cervids are neither geometrically nor elastically similar: Exponents for most relationships lie between elastic and geometric values. Differences in scaling between cervids and Bovidae are in part a consequence of the difference in size range between the two families. Departures from regular allometric trends in limb lengths were analysed by scaling the length of each limb bone against femur length, and calculating the difference between the actual and the expected length. Small cervids living in dense forest tend to have moderate length or markedly shorted limbs while Hydropotes has elongated limb segments. Most cervids weighing between 40-100 kg have elongate segments. These species are specialized for rapid, highly maneuverable locomotion and for clearing obstacles. Cervids larger than 100 kg generally have shortened limb segments. In large cervids, as in large ungulates generally, specializations for speed may not be as important as in smaller cervids.