A 6000 Year Old Fossil Dugong from Botany Bay: Inferences about Changes in Sydney's Climate, Sea Levels and Waterways

The excavation in the 1890s of a skeleton of the warm-water marine mammal 'Dugong dugon', associated with Aboriginal artefacts, from a Botany Bay salt marsh, marked the beginning of speculation about climate and sea level change in Australia over the period of human occupation. The dugong bones have recently been dated, giving a conventional ¹⁴C age of 5520±70 years BP, which is consistent with three older ¹⁴C dates for a layer of buried trees that underlies much of the north Botany sediments. The carefully drawn cross-sections of depositional strata produced by the original discoverers allow further interpretation of the pattern of Holocene sea-level fluctuations in the Sydney region. Layers of estuarine sediment, such as the one containing the dugong skeleton, are inter-bedded with peat layers containing 'in situ' roots and stumps, suggesting that the site alternated between sub-aerial exposure and submergence throughout the Holocene. The presence of the dugong is suggestive of warmer conditions, and its inland location indicates a more extensive Botany Bay in the recent past. This is in agreement with other work from southern New South Wales describing both warm-water marine species and higher sea levels several thousand years ago.