Abstract
Only two Jeffersonian mammoths (Mammuthus jeffersonii) have been confirmed in the northwestern United States. This study focuses on the specimen excavated in 1966 in Conda, ID. The mammoth was radiocarbon dated to 13,500 cal yr BP, during the Bolling-Allerod interstadial period, a time of intense climatic warming and environmental change. While research shows that Jeffersonian mammoths in the Midwest were common in mesic environments and consumed C4 grasses and shrubs (Saunders et al., 2010), little is known about the dietary patterns of Jeffersonian mammoths in the western US. This study utilizes stable isotope ratios of C and O from molar enamel to determine the diet and migration patterns of the mammoth.
Using known growth rates of Columbian mammoth molars, the tooth was sampled at 1.2 cm intervals to create a 13-year timeline of delta (super 13) C and delta (super 18) O values. Each of the 13 samples represents a yearly average. delta (super 13) C (VPDB) values of the molar enamel varied from -7.7 per mille to -10.2 per mille, indicating that the mammoth was consuming a diet that was primarily dominated by C3 vegetation. The youngest sample showed that the mammoth consumed a diet with 34.0% C4 vegetation, while the oldest is only 15.6%. This indicates that either a lack of food sources led to an expanded diet, or the mammoth migrated to a place with more C (sub 4) grasses. delta (super 18) O (VSMOW) values ranged from 16.4 per mille to 19.6 per mille. After calibrating the oxygen enamel values to drinking water, delta (super 18) O values varied between -13.4 per mille and -16.6 per mille. This 3.2 per mille range indicates that the mammoth was consuming water with relatively consistent delta (super 18) O values, supporting the interpretation that the mammoth likely had to expand its diet, rather than migrate to find food.