ANN ARBOR, MICHIGAN—Daniel Fisher, director of the University of Michigan Museum of Paleontology, and his graduate students have shown in the past that “life history” information, such as growth rates, age of sexual maturation, and spacing of pregnancies is preserved in fossil mammoth tusks. Now graduate student Michael Cherney has analyzed the isotopic composition of 40,000-year-old to 10,000-year-old tusks from 15 mammoths ranging in age from three to 12 at the time of death in order to determine how old they were when they were weaned from mother's milk. The numbers suggest that the years that a calf nursed decreased by about three years over a span of 30,000 years. In modern elephants, climate change is associated with delayed weaning; pressure from hunting results in earlier weaning age. “This shift to earlier weaning age in the time leading up to woolly mammoth extinction provides compelling evidence of hunting pressure and adds to a growing body of life-history data that are inconsistent with the idea that climate changes drove the extinctions of many large ice-age mammals,” Cherney said in a press release. To read about a recent discovery, go to "Butchered Mammoth Bones Unearthed in Michigan."