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Master of Science (MS) in Biology
The Lake Eyre Basin in South Australia holds Australia’s oldest known fossil marsupials representing both extant and extinct families in the Etadunna Formation, a formation that spans nearly two million years from 23.3 to 25 MA. During that two-million-year period, the terrestrial herbivorous marsupials present in the area underwent a dramatic transition both taxonomically and dentally, likely brought on by a changing environment caused by a warming climate. However, it is unknown whether a similar change occurred to the marsupials like possums that live up in the canopy. Understanding this could help determine how extensively this change in the environment affected the marsupials in this region. In Australian possums, the third premolar in particular shows the greatest morphological diversity and is therefore the best indicator of the possum’s dietary niche. These premolars can be wide and bladed to small and conical to tall and canine-like. The size and shape of third premolars can be correlated with molar shape to determine diet through Kendall’s ranked correlation. Additionally, a microwear analysis can help further narrow down possible dietary niches. Microwear refers to the microscopic pits and grooves in teeth created by food substrate grinding against the teeth during chewing. The ratio of scratches to pits is determined by the physical qualities of the food, including its hardness, toughness, plasticity, and strength. The third premolars in possums provide large occlusal surfaces, making them ideal candidates for studying microwear. Areas of 0.6 mm x 0.6 mm on the occlusal surfaces of the upper and lower third premolars were studied. After the dietary niches of the possum species were determined, these niches were charted based on when in the formation each of the different species lived to see if the dietary niches of the possums changed over time. The result showed that the seven different families of possums followed one of four trends. The families of Pseudocheiridae and Ektopodontidae experienced minimal changes over the course of this two-million-year period. Burramyidae experienced a taxonomic and dietary transition during this time. Miralinidae and Pilkipildridae went through a local extirpation. Finally, there was not enough data to determine changes in the Phalangeridae and Petauroidae families during this time.
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Wheat, Theodore C., "Evolution of the diets of Australian Possums (Marsupialia: Phalangeriformes) from the Etadunna Formation in the Lake Eyre Basin, South Australia" (2023). EWU Masters Thesis Collection. 896.