These differences may explain why the mammoths are no longer alive, he added.
The often worn and broken tips of adult tusks, however, present a problem, Rountrey said.
Missing tips mean that the earliest years of mammoth life remain poorly understood and age estimates for adults are imprecise.
To improve their estimates the researchers decided to look for a signature that might be preserved in tusks of both adults and juveniles, such as signs of when a mammoth was weaned.
In particular the researchers looked at changes in different nitrogen isotopes, a chemical signature in the tusk that can be tied to feeding on breast milk.
"Milk would have a higher proportion of [those isotopes] than the plants a mammoth might eat, and that difference shows up in the calf's tusk," Rountrey said.
This data can also help the researchers determine the age of an animal when weaning occurred.
Extended Nursing
In their weaning study, Fisher and his colleagues analyzed a juvenile woolly mammoth tusk from Wrangel Island in northern Siberia.
They presented their findings last month at the annual meeting of the Society of Vertebrate Paleontology in Mesa, Arizona. The weaning of the mammoth took place gradually over a period of about six years, they said.
African elephants by comparison wean about three and half years in favorable climate conditions. Under poor climate conditions, such as drought, the elephants may not wean until five and a half years, Rountrey said.
The tusk research suggests that a harsh Arctic climate where this mammoth lived required a supplement to its diet, especially during the winter months.
"Perhaps this animal … could have shifted its diet to include more vegetation during the spring and summer and been less dependent on milk," Rountrey said.
The researchers are currently conducting additional studies on juvenile mammoth tusks from different times and places to get a feel for how weaning differed in various climate conditions and over time.
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