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.

Lineage zones within nine contemporaneous mammalian lineages represented in the Cenozoic fossil vertebrate record from the Riversleigh World Heritage Area in northern Australia are used to resolve a series of faunal intervals from the Late Oligocene to Late Miocene. The results agree with previous interpretations of Cenozoic biostratigraphy, provide evidence for the presence of time horizons subdividing some of the four previously recognized Riversleigh biochrons A–D and also provide evidence supporting the allocation of a greater number of Riversleigh faunas to intervals within the Riversleigh biochronology than other methods in previous work. This approach demonstrates the biostratigraphical potential of evolutionary lineages.

Using demonstrated relationships between body mass and humeral and femoral circumferences, we calculate the weight of the only specimen of Thylacoleo carnifex known from a near-complete skeleton. Body weights of 112–143 kg were estimated for this individual, from Moree, north-western New South Wales. Extrapolating on the basis of geometric similtude, we further estimated the weight of the largest T. carnifex for which we had cranial data at 128–164 kg. Moreover, estimates for at least three of the thirteen available specimens exceeded 124–160 kg, suggesting that individuals of this size were common. Our estimates of average weight for the species range from 101 to 130 kg. These results clearly show that Pleistocene Australia had a 'large' cat equivalent and that 'large' terrestrial predator niches were not then occupied exclusively by reptiles.They may also diminish the argument that soil-nutrient deficiency constrained the evolution of large mammalian carnivores on this continent in the Pleistocene. Similarly, we posit that prima facie evidence for reptilian domination of terrestrial carnivore niches during the Miocene is wanting, although it is conceded that far more detailed investigation is required to comprehensively test these hypotheses. Earlier studies have drawn parallels between T. carnifex and sabre-toothed predators, thought to have specialised in hunting particularly large and powerful prey. Taken in the context of upwardly revised weight estimates, we argue that Pleistocene marsupial lions may have dispatched even Diprotodon-sized animals. But again, more comprehensive study, including thorough biomechanical design analysis of the post-cranial skeleton in particular, will be required to thoroughly illuminate the predatory habitus and general ecology of Australia's largest and most specialised marsupial carnivore.

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.