Meeting Abstract
Femoral measurements are often used to estimate the body size of extant crocodylians and their extinct ancestors when snout-vent length (SVL) or mass cannot be measured directly. These relationships are often based on osteological specimens that lack sex data and do not account for sex. However, sex is an important determinant of crocodylian body size; most extant species are sexually size dimorphic, usually with larger males. Size differences may result from differences in scaling trajectory, growth rate, or growth duration; if males and females differ significantly in their ontogenetic scaling trajectories, the accuracy of current size predictive models is questionable. We measured 224 femora from a single population of wild Spectacled caiman ranging in size from near-hatchlings to large adults. All specimens have associated sex, mass, SVL, and total length (TL) data. We used ordinary least squares linear regression to describe the relationships among several femoral measurements, SVL, TL, and mass. To test whether caimans show sex differences in proportions or scaling trajectories unrelated to overall body size, we performed an analysis of covariance for each regression. Male and female scaling relationships cannot be statistically distinguished from each other or from pooled-sex data, suggesting that femoral estimates of crocodylian body size do not need to account for sex. We also constructed skeletochronological growth curves using a subset of 66 individuals. Males grow much faster than females until sexual maturity, but afterwards grow similarly. Although femoral proportions are not sexually dimorphic, differences in growth rate suggest that size in combination with relative morphological maturity (e.g. presence of femoral muscle scars) may be useful to estimate sex of skeletal specimens.
