Scaling pattern of the carnivoran forelimb: Locomotor types, differential scaling and thoughts on a dying similarity

The scaling pattern of the forelimb in Carnivora was determined using a sample of 30 variables measured on the scapula, humerus, radius, ulna, and third metacarpal, of 429 specimens belonging to 137 species of Carnivora. Standardized major axis regressions on body mass were calculated for all variables, using both traditional regression methods and phylogenetically independent contrasts (PIC). In agreement with previous studies on the scaling of the appendicular skeleton, conformity to either the geometric similarity hypothesis or the elastic similarity hypothesis was low. The scaling pattern of several phyletic lines and locomotor types within Carnivora was also determined, and significant deviations from the scaling pattern of the order were found in some of these subsamples. Furthermore, significant evidence for differential scaling was found for several variables, both in the whole sample and in various phylogenetic and locomotor subsamples. Contrary to previous studies, significant differences were found between the allometric exponents obtained with traditional and PIC regression methods, emphasizing the need to take into account phylogenetic relatedness in scaling studies. In light of these and previous results, we conclude that similarity hypotheses are too simplistic to describe scaling patterns in the carnivoran appendicular skeleton, and thus we propose that scaling hypotheses should be built from similarities in the scaling patterns of phylogenetically narrow samples of species with similar locomotor requirements. The present work is a first step in the study of those samples.