Minimum convex hull mass estimations of complete mounted skeletons

Abstract

Body mass is a critical parameter used to constrain biomechanical and physiological traits of organisms. Volumetric methods are becoming more common as techniques for estimating the body masses of fossil vertebrates. However, they are often accused of excessive subjective input when estimating the thickness of missing soft tissue. Here, we demonstrate an alternative approach where a minimum convex hull is derived mathematically from the point cloud generated by laser-scanning mounted skeletons. This has the advantage of requiring minimal user intervention and is thus more objective and far quicker. We test this method on 14 relatively large-bodied mammalian skeletons and demonstrate that it consistently underestimates body mass by 21 per cent with minimal scatter around the regression line. We therefore suggest that it is a robust method of estimating body mass where a mounted skeletal reconstruction is available and demonstrate its usage to predict the body mass of one of the largest, relatively complete sauropod dinosaurs: Giraffatitan brancai (previously Brachiosaurus ) as 23200 kg.

Reconstruction of the musculoskeletal system in an extinct lion

“…Whilst convex hull models can produce realistic estimates for total mass, they will produce TABLE 3. Vertebral muscle belly and tendon lengths and masses as predicted from Cuff et al (2016a, b regional variability, with the limb masses generally underestimated, and the core body overestimated (Sellers et al, 2012;Brassey and Sellers, 2014). The muscled reconstruction of P. atrox showed how much variability was obtained for the limb morphology ( Figure 5).…”

“…15 -16% (Pitts and Bullard, 1968)). Convex hull models have been used recently to reconstruct body segmental shapes and estimate body masses for skeletons with no preserved soft tissues (e.g., Sellers et al, 2012;Basu et al, 2016;Bates et al, 2016;Brassey et al, 2016). The convex hull model for the entire skeleton of P. atrox produced a volume of 0.185 m 3 (Figure 4).…”

“…The convex hull model for the entire skeleton of P. atrox produced a volume of 0.185 m 3 (Figure 4). Using the range of potential densities (Sellers et al, 2012), the body mass estimates varied from 180 kg to 219 kg. The mid-point of these two extreme ranges is 200 kg, only a few kilograms away from the ~207 kg estimate obtained from the bones, which is unsurprising as the composite bones were scaled to the 207 kg estimate.…”

“…Convex hull bones ("CHB") is the convex hull range of masses and the convex hull muscles ("CHM") is the convex hull range of masses from the muscled reconstructions. The masses for both convex hull methods were calculated from the volumes using only the mean density [893.36 kg m −3 multiplied by 1.206 (Sellers et al, 2012)]. Ratios of each of these estimates are shown in the final four columns on the right side of the table.…”

“…This was done by using the "convex hull" filter within Meshlab for the skeletal elements from each of the body segments (e.g., Basu et al, 2016). Body mass estimates were calculated from the sum of all masses from the complete set of convex hulls using a 4 range of densities from 893.36 kg m −3 multiplied by 1.091 to 1.322 (i.e., 974.7 kg m −3 to 1181 kg m −3 -a correction factor due to the underestimation of limb masses) (Sellers et al, 2012). In addition to total body mass estimations, convex hull estimates were made of the individual limb segments and compared to the values from the reconstructions.…”