COMPOSITIONAL VARIATION IN THE TUSK DENTIN OF A JUVENILE AFRICAN ELEPHANT AND A JUVENILE WOOLLY MAMMOTH: SEASONAL PATTERNS AND WEANING

Proboscidean tusk dentin provides information on diet, climate, and nutritional status through analyses of variation in periodic growth increment thickness and compositional time series. Data from tusks can be used to reconstruct life histories of extinct taxa, providing information on life history responses to climate change or human pressure. There has been some work on modern elephant tusks, but additional data from modern animals are needed as references for work on fossils. The focus of this study is variation in growth increment thickness and composition of dentin samples from tusks of a juvenile elephant and a juvenile mammoth. Tusks of juveniles are of interest because the part of a tusk formed during this period is often missing in tusks of adults. Thus, little is known of the patterns of structural or compositional variation recorded in tusks during the first years of life. Serial compositional analyses (δ¹³C, δ¹⁵N, δ¹⁸O, and ratios of Mg, P, Mn, Fe, Zn, Sr, Ba, and Pb to Ca) were performed on the tusk dentin of a juvenile African elephant from Hwange National Park, Zimbabwe, and a juvenile woolly mammoth from Wrangel Island, Russian Federation. The elephant has a constrained date of death, and weather records for the period of its life are available.

The elephant tusk shows δ¹⁵N patterns consistent with higher milk intake in the first year of life, followed by seasonal oscillations. δ¹³C shows seasonal oscillations due to changes in the ratio of C₃ to C₄ plants in the diet. This pattern is correlated with weather data, and the pattern of seasonal diet change is consistent with results of other studies of elephants in Hwange. There is also compositional evidence of seasonal fluctuation in the relative importance of milk in the diet.

The mammoth tusk shows a long-term decrease in δ¹⁵N, and seasonal variation in δ¹⁵N, δ¹³C, and δ¹⁸O. The decrease in δ¹⁵N is consistent with a gradual decrease in the importance of milk in the diet. In-phase seasonal variation in δ¹⁵N and δ¹³C may indicate that the importance of milk in the diet also varied seasonally.

This and other ongoing work suggests that stress-sensitive life history parameters such as weaning age can be determined for mammoths. Tracking changes in such parameters through time may provide insights into how mammoths responded to changing environments.