Prediction of marsupial body mass

Abstract

Cranio-dental variables are correlated with body mass in marsupials, using a species data-set derived from extant australidelphian representatives, to predict body mass in fossil species. Thirty-eight extant australidelphian species, including 10 dasyuromorphians, 22 diprotodontians, 1 notoryctomorphian and 5 peramelemorphians, were analysed. Where sexual dimorphism was prominent, genders were evaluated separately. Twenty-nine cranio-dental variables were measured for each specimen and species averages calculated. Body masses were taken as recorded for each specimen or as published species averages. The cranio-dental measures for each morpho-species were then regressed against average body mass in four distinct data-sets: (1) the entire species sample, (2) only dasyuromorphian taxa, (3) only diprotodontians, and (4) all species excluding dasyuromorphians. Each cranio-dental variable was then ranked according to various error statistics and correlation coefficients. Results suggest that predictors of body size in eutherians (such as first lower molar area), commonly used to estimate body mass in marsupials may not be reliable or accurate indicators. Significant differences in the usefulness of predictor variables between taxonomic data-sets were also observed. Total jaw length is the most reliable predictor for diprotodontians, as well as for all species combined, whereas lower molar row length appears to be more appropriate for dasyuromorphians. Multiple variable regressions variably offer more precision than those derived from individual parameters. On the basis of these data, body mass estimations are provided for a number of extinct marsupial taxa.