Data from: Extrapolating body masses in large terrestrial vertebrates

Despite over a century of interest, body mass estimation in the fossil record remains contentious, particularly when estimating the body mass of taxa outside the size scope of living animals. Such situations require methodological extrapolations leading some to suggest that extant-based linear scaling models, such as that between stylopodial circumferences and body mass, may overestimate the body masses of large terrestrial vertebrates. Here I test the implicit assumption of such assertions: that a quadratic model provides a better fit to the combined humeral and femoral circumferences-to-body mass relationship. I then examine the extrapolation potential of these models through a series of subsetting exercises in which lower body mass sets are used to estimate larger sets. Model fitting recovered greater support for the original linear model, and a non-significant second-degree term indicates that the quadratic relationship is, statistically, linear. Nevertheless, some statistical support was obtained for the quadratic model, and application of the quadratic model to a series of dinosaurs provides lower mass estimates at larger sizes that are more consistent with recent estimates using a minimum convex hull (MCH) approach. Given this consistency, a quadratic model may be preferred at this time. Still, caution is advised; extrapolations of quadratic functions are unpredictable compared to linear functions. Further research testing the MCH approach (e.g., the use of a universal up-scaling factor) may shed light on the linear vs. quadratic nature of the relationship between the combined femoral and humeral circumferences and body mass.