Body-Mass Estimation in Paleontology: A Review of Volumetric Techniques

Abstract

Body mass is a key parameter for understanding the physiology, biomechanics, and ecology of an organism. Within paleontology, body mass is a fundamental prerequisite for many studies considering body-size evolution, survivorship patterns, and the occurrence of dwarfism and gigantism. The conventional method for estimating fossil body mass relies on allometric scaling relationships derived from skeletal metrics of extant taxa, but the recent application of three-dimensional imaging techniques to paleontology (e.g., surface laser scanning, computed tomography, and photogrammetry) has allowed for the rapid digitization of fossil specimens. Volumetric body-mass estimation methods based on whole articulated skeletons are therefore becoming increasingly popular. Volume-based approaches offer several advantages, including the ability to reconstruct body-mass distribution around the body, and their relative insensitivity to particularly robust or gracile elements, i.e., the so-called 'one bone effect.' Yet their application to the fossil record will always be limited by the paucity of well-preserved specimens. Furthermore, uncertainties with regards to skeletal articulation, body density, and soft-tissue distribution must be acknowledged and their effects quantified. Future work should focus on extant taxa to improve our understanding of body composition and increase confidence in volumetric model input parameters.

Ontogenetic changes in the body plan of the sauropodomorph dinosaur Mussaurus patagonicus reveal shifts of locomotor stance during growth

“…Both convex hull modelling and spline-based approaches are commonly used for estimating the mass of extant and fossil species, and tend to produce roughly similar body mass estimates; as in this study. Convex hull modelling is quick in comparison to spline-based models and is relatively more objective 42 . However, we have concerns that convex hull models, especially for sauropsid tetrapods with large tails and pelvic limbs, can produce CoM estimates that are inaccurate for those segments and for the whole body (e.g.…”

First partial skeleton of Delphinornis larseni Wiman, 1905, a slender-footed penguin from the Eocene of Antarctic Peninsula

“…According to Jadwiszczak and Chapman (2011, figure 1), rough estimates obtained by Jadwiszczak (2001) via the modelling of the tarsometatarsal dorsoplantar width and overall body length relationship, suggest that small individuals assignable to D. larseni, and NRM-PZ A.994 is not that large, could have been slightly shorter than some extant Gentoo penguins, Pygoscelis papua. Considering longer weight-bearing bones, femoral shaft and head dimensions are often utilized in body-mass assessments (e.g., Brassey, 2016). Taking cognizance of femoral dimensions, the studied skeleton belonged to an individual both shorter and lighter than whichever representative of so-called giant penguins (e.g., Jadwiszczak and Chapman, 2011) from the Eocene of Seymour Island.…”

Lower rotational inertia and larger leg muscles indicate more rapid turns in tyrannosaurids than in other large theropods

“…In addition to our mathematical slicing procedures (Henderson, 1999), methods for calculating mass properties include use of simplified B-splines or convex hulls to represent body regions (Hutchinson, Ng-Thow-Hing & Anderson, 2007; Sellers et al, 2012; Brassey & Sellers, 2014; Brassey et al, 2016), or more complex non-uniform rational B-spline reconstruction modified to fit the contours of mounted skeletons and inferred soft tissues (Bates et al, 2009a, 2009b; Mallison, 2007, 2010, 2014; Stoinski, Suthau & Gunga, 2011). Brassey (2017) reviews and compares these methods in detail. Both spline-based and mathematical slicing methods have been validated for living terrestrial vertebrates (Henderson, 1999, 2004, 2006; Henderson & Snively, 2003; Hutchinson, Ng-Thow-Hing & Anderson, 2007; Bates et al, 2009a).…”