Leveraging functional morphology to increase accuracy of body mass estimation: A study using canids

Body mass is an important facet of reconstructing the paleobiology of
fossil species, and has, historically, been estimated from individual
skeletal measurements. This paper demonstrates the potential advantages of
estimating body mass using 3D geometric morphometrics on limb bones, which
allows size to be explicitly contextualized within the functional
morphology of the animal. Geometric morphometrics of the humerus and femur
is used to estimate body mass in domestic dogs and wild canids, and the
resulting estimates are compared to estimates made using limb bone
dimensions and centroid size. In both groups, 3D methods produced more
accurate estimates of body mass than linear dimensions. Additionally,
centroid size was a poor predictor of body mass and should not be
preferred over linear measurements. The use of 3D methods also reveals
specific aspects of shape that are associated with different sizes. In
general, relatively heavier individuals were associated with more robust
bones and wider articulation sites, as well as larger attachment sites for
muscles related to flexion and extension of the shoulder and hip joints.
The body mass equations constructed based on dogs were further evaluated
on wild canids, as a test of their potential efficacy on fossil canids.
With some adjustments, the body mass estimation equations made for
domestic dogs were able to reliably predict the mass of wild canids. These
equations were then used to estimate body mass for a selection of fossil
canids: Canis latrans, 16 kg; Aenocyon dirus, 67 kg; Phlaocyon
multicuspus, 8 kg; and Hesperocyon gregarious, 2.5 kg.