STABLE ISOTOPE ECOLOGY OF EXTANT MOUNTAIN AND COMMON BRUSHTAIL POSSUMS

Understanding the paleoecology of mammals is possible through the geochemical analysis of teeth in a range of mammals, providing critical information about ancient environments. However, before diets and ecology can be assessed, it is first critical to clarify the stable isotope ecology of extant taxa, including elucidating how mammals record their local environments. Small arboreal marsupials are abundant in ancient Australian ecosystems, particular during the Miocene when forests were more widely distributed. However, our understanding of their stable isotope ecology and relationship to local precipitation and climate variables is not well understood. Here, we assessed the stable isotope ecology of the common brushtail possum (Trichosurus vulpecula; a widespread taxon inhabiting every state and territory in Australia) and the mountain brushtail possum (Trichosurus caninus; a taxon with a highly restricted geographic range). Specifically, we sampled the incisor enamel of T. caninus and T. vulpecula and analyzed their stable carbon and oxygen isotopes. In areas where these taxa overlap in latitudinal extent (between -28 and -24 degrees North latitude), T. caninus has significantly lower mean δ¹³C values and mean δ¹⁸O values than T. vulpecula despite having indistinguishable latitudinal mean values from sampled specimens. Lower mean δ¹³C values in T. caninus suggest that it occupies denser canopied forests and/or feeds lower in the canopy than T. vulpecula, while further work is needed to clarify how these species track local climates via δ¹⁸O values. While T. vulpecula δ¹³C and δ¹⁸O values are positively correlated with latitude, they are also positively correlated with each other - suggesting that these possums likely acquire most of their water from leaf material (much like tapirs in the Amazon do today). Further, T. vulpecula δ¹⁸O values are positively correlated with meteoric water. Future work will focus on better understanding how precipitation and temperature affect possum stable isotope ecology– of relevance to clarifying ancient forest ecosystems in Australia through the stable isotope ecology of fossil arboreal marsupials.