A universal scaling relationship between body mass and proximal limb bone dimensions in quadrupedal terrestrial tetrapods

Abstract

BackgroundBody size is intimately related to the physiology and ecology of an organism. Therefore, accurate and consistent body mass estimates are essential for inferring numerous aspects of paleobiology in extinct taxa, and investigating large-scale evolutionary and ecological patterns in the history of life. Scaling relationships between skeletal measurements and body mass in birds and mammals are commonly used to predict body mass in extinct members of these crown clades, but the applicability of these models for predicting mass in more distantly related stem taxa, such as non-avian dinosaurs and non-mammalian synapsids, has been criticized on biomechanical grounds. Here we test the major criticisms of scaling methods for estimating body mass using an extensive dataset of mammalian and non-avian reptilian species derived from individual skeletons with live weights.ResultsSignificant differences in the limb scaling of mammals and reptiles are noted in comparisons of limb proportions and limb length to body mass. Remarkably, however, the relationship between proximal (stylopodial) limb bone circumference and body mass is highly conserved in extant terrestrial mammals and reptiles, in spite of their disparate limb postures, gaits, and phylogenetic histories. As a result, we are able to conclusively reject the main criticisms of scaling methods that question the applicability of a universal scaling equation for estimating body mass in distantly related taxa.ConclusionsThe conserved nature of the relationship between stylopodial circumference and body mass suggests that the minimum diaphyseal circumference of the major weight-bearing bones is only weakly influenced by the varied forces exerted on the limbs (that is, compression or torsion) and most strongly related to the mass of the animal. Our results, therefore, provide a much-needed, robust, phylogenetically corrected framework for accurate and consistent estimation of body mass in extinct terrestrial quadrupeds, which is important for a wide range of paleobiological studies (including growth rates, metabolism, and energetics) and meta-analyses of body size evolution.

Maiasaura, a model organism for extinct vertebrate population biology: a large sample statistical assessment of growth dynamics and survivorship

“…Tibia specimens of this size in our sample demonstrate the presence of an external fundamental system (EFS), so ROM 44770 is likely a skeletally mature individual. A body mass approximation of 3833 ± 958 kg (N. Campione personal communication 2013) for ROM 44770 was obtained from humerus and femur circumference measurements and using the phylogenetically corrected equation of Campione and Evans (2012). Our dataset consists only of tibiae, so we were unable to use the method of Campione and Evans (2012) to determine body mass for individuals in our sample.…”

A new multi-faceted framework for deciphering diplodocid ontogeny

“…Additional mass estimation methods that incorporate multiple elements (such as humeral and femoral circumference; i.e., Campione and Evans, 2012) and histologic data (Sander and Tückmantel, 2003;Lehman and Woodward, 2008;Griebeler et al, 2013) should produce more accurate estimates because these methods incorporate more variables regarding the individual and its life history. However, the diplodocid dataset in this analysis lacks the required inclusive life history variables (i.e., corresponding femur and humerus [Campione and Evans, 2012], or histologic markers -LAGs or polish lines [Sander and Tückmantel, 2003;Griebeler et al, 2013]). As such the most agreeable method that can be incorporated with this dataset is that of Mazzetta et al (2004).…”

Mandibular and dental characteristics of Late Triassic mammaliaform Haramiyavia and their ramifications for basal mammal evolution

“…S2 and S3). The body mass of Haramiyavia is estimated to be 47 g by a regression to humeral length (log 10 body mass = 2.8626 × log 10 humerus length − 1.8476) based on a dataset of extant mammals (42).…”