An alternative method for predicting body mass: the case of the Pleistocene marsupial lion

Abstract

Accurate estimates of body mass in fossil taxa are fundamental to paleobiological reconstruction. Predictive equations derived from correlation with craniodental and body mass data in extant taxa are the most commonly used, but they can be unreliable for species whose morphology departs widely from that of living relatives. Estimates based on proximal limb-bone circumference data are more accurate but are inapplicable where postcranial remains are unknown. In this study we assess the efficacy of predicting body mass in Australian fossil marsupials by using an alternative correlate, endocranial volume. Body mass estimates for a species with highly unusual craniodental anatomy, the Pleistocene marsupial lion (Thylacoleo carnifex), fall within the range determined on the basis of proximal limb-bone circumference data, whereas estimates based on dental data are highly dubious. For all marsupial taxa considered, allometric relationships have small confidence intervals, and percent prediction errors are comparable to those of the best predictors using craniodental data. Although application is limited in some respects, this method may provide a useful means of estimating body mass for species with atypical craniodental or postcranial morphologies and taxa unrepresented by postcranial remains. A trend toward increased encephalization may constrain the method's predictive power with respect to many, but not all, placental clades.

Ecological and evolutionary significance of sizes of giant extinct kangaroos

“…Previous estimates of body mass for megafaunal kangaroos generally derive from extrapolations based on univariate skull and dental measurements (Flannery 1980;Murray 1991), but these types of comparisons are potentially unreliable (Myers 2001;Wroe et al 2003Wroe et al , 2004. Cranial metrics may be determined and/or tightly constrained by feeding requirements, and dental dimensions are particularly problematic for macropodids, in which molars erupt continually and are successively shed.…”

“…With one exception drawing from comparisons of endocranial volume (concentrating mainly on non-macropodids: Wroe et al 2003), only 'rule of thumb' or 'best guess' body mass estimates exist for any of these fossil species (Johnson and Prideaux 2004). For example, on the basis of extrapolations from linear measurements, Murray (1991) estimated a mass of <150 kg for the largest Pleistocene kangaroo, Procoptodon goliah, and 25-80 kg for most other sthenurines.…”

Ecomorphological determinations in the absence of living analogues: the predatory behavior of the marsupial lion (Thylacoleo carnifex) as revealed by elbow joint morphology

“…Thylacoleo thus represents an extinct hypercarnivorous species without living analogs (Wroe 2000), as all living diprotodontids are omnivores or herbivores (e.g., Finch 1982;Wells et al 1982Wells et al , 2009Case 1985;Wroe et al 2000;Wroe 2003).…”

“…youngest species of the genus Thylacoleo (T. crassidentatus and T. hilli being known from the Pliocene), the largest member of all thylacoleonids (ca. 100-160 kg; Wroe et al 1999;Wroe et al 2003), and the most geographically dispersed of the three.…”

“…The family Thylacoleonidae belongs to the order Diprotodontia (Mammalia; Metatheria), which today comprises only omnivorous or herbivorous forms such as possums, koalas, wombats and kangaroos (e.g., Finch 1982;Wells et al 1982Wells et al , 2009Case 1985;Wroe et al 2000;Wroe 2003 Gill 1954). However, all of the evidence obtained during the last few decades, from both adaptive (Finch 1982;Wells et al 1982;Wroe et al 2005;Wroe et al 2008) and ecophysiological (Nedin 1991;Gröcke 1997;Wells et al 1982) …”