Bennett’s wallaby ( Macropus rufogriseus) marrow quality vs quantity: evaluating human decision-making and seasonal occupation in late Pleistocene Tasmania

Abstract

A pilot study on the fatty acid composition of the bone marrow, brain tissue and muscle (flesh) of the medium-sized marsupial the Bennett’s wallaby ( Macropus rufogriseus), aimed to explore the mechanisms behind the dominance of this human prey species in late Pleistocene southwest Tasmania. In particular it was designed to investigate why humans frequently selected and transported the wallaby hindquarters, breaking open their longbones and metatarsals to expose the marrow cavity, when these animals could easily have been transported whole. Initial results indicated that the percentage of unsaturated fatty acids particularly palmitoleic acid (C 16:1) and oleic acid (C 18:1) in the bone marrow increased distally away from the body core temperature or the heart, towards the hands and feet. There is a corresponding decrease in the percentage of the saturated fatty acids, particularly palmitic acid (C 16:0) and stearic acid (C 18:0). This is similar to the pattern identified in placental artiodactyls (even-toed ungulates) and rodents. The preliminary study was then expanded to a year-long seasonal experiment involving wallabies from different Tasmanian environmental and climatic zones to see if this can better help explain the apparent seasonal occupation of caves indicated from recent Bennett’s wallaby teeth annuli (Skeletochronological studies). It was found that the Bennett’s wallaby remained a relatively stable and dependable resource throughout the year, with environmental, altitudinal and seasonal variability having only a minor effect on the fatty acid composition or nutritional quality of their bone marrow, muscle and brain tissue. Interestingly, the animals had increased desirable unsaturated fatty acids in their marrow, muscle and brain during the winter and spring with decreased amounts during the summer and autumn. This lends support to an earlier Kidney Fat Index (KFI) analysis for the Bennett’s wallaby which recorded significant seasonal differences within and between regions, indicating an environmental effect on overall body condition. Fatty acid analysis of the Common wombat Vombatus ursinus, the Tasmanian pademelon Thylogale billardierii, and the Forester or Eastern Grey kangaroo Macropus giganteus were also included to ascertain why these animals remained constant, although minor, prey species throughout the late Pleistocene. While the results from these animals were similar to the Bennett’s wallaby, there were some unexpected and surprising patterns that require further investigation. All of these fatty acid analyses have important implications for understanding human decision-making and occupation of southwest Tasmania during the Last Glacial Maximum, for modern dietary and palaeodietary benefits, and for understanding the physiology of these unique Australian marsupials.