STABLE ISOTOPE PALEOBIOLOGY OF THE NOVA SCOTIA MASTODONS (MAMMUT AMERICANUM)

The late Pleistocene fossil record in Nova Scotia, Canada preserves a unique window into the life of American mastodons (Mammut americanum) during a period of climate transition prior to the onset of the Wisconsinan glaciation (ca. 75 ka years BP). Because mastodon remains dating to this period are quite rare, the Nova Scotian fossils provide important information for understanding mastodon paleobiology during a time when environmental conditions are thought to have been favourable for survival. Here we use carbon (δ¹³C) and oxygen (δ¹⁸O) stable isotope analysis of tooth enamel to investigate the paleobiology of mastodons in Atlantic Canada. Specifically, we combine bulk (one enamel sample per tooth) and serial (multiple samples along the tooth growth axis) sampling strategies to examine changes in diet, environment, and climate during tooth formation. Bulk δ¹⁸O values (n = 6, mean = -8.36‰) of the Nova Scotia mastodons are depleted relative to contemporaneous mastodons in the southern United States. This pattern is consistent with cooler temperatures at higher latitudes. Bulk δ¹³C values (mean calculated δ¹³C_diet = -26.4 ‰) indicate the consumption of C₃ plants in accordance with previous paleobotanical studies. Serial sequences show cyclic variation in δ¹⁸O values with a mean amplitude of 2.10‰, suggesting that the mastodons experienced moderate intra-annual fluctuations in ambient temperature. The range of δ¹⁸O values and seasonal amplitudes for each individual are relatively consistent throughout the period of tooth formation, indicating that the mastodons likely remained within a local home range where the isotopic compositions of drinking water varied seasonally in a similar fashion each year. The range of intra-annual δ¹³C values suggest that the mastodons consumed an exclusively C₃ diet year-round (calculated δ¹³C_diet range = -28.1‰ to -25.0‰), with no evidence of seasonal mixed feeding. Mean amplitude of δ¹³C variation is relatively low (1.05‰) indicating that the mastodons did not experience significant seasonal shifts in diet. Seasonal changes in selectivity of certain plant taxa or plant parts could account for the degree of δ¹³C variation observed here. Collectively, these findings further refine our understanding of mastodon paleobiology and provide a baseline for interpreting climatically driven changes in dietary and ranging behaviour.