Woolly Mammoth Tusks Yield Clues to Animals' Lives

John Roach
for National Geographic News

November 22, 2005

A woolly mammoth that died millennia ago nursed for at least six years, according to an analysis of one of its tusks. The finding raises the question: Did its mother finally get tired of being poked?

"That's an interesting question," said Adam Rountrey, a graduate student in geology at the University of Michigan in Ann Arbor who helped analyze the tusk. "At this age the tusks are not protruding very far, but sure, eventually they could get in the way."

Rountrey and his advisor, Daniel Fisher, are analyzing the chemical signatures in mammoth tusks to better understand the lives of the ancient elephantlike creatures and gain insight to the cause of their extinction.

Mammoth tusks grow a little bit every day. As growth rings reveal a tree's age, markings and chemical signatures in tusks help scientists tease out details like when a mammoth reached maturity and what it ate.

Fully grown mammoths stood 10 to 12 feet (3 to 3.7 meters) tall and weighed between 12,000 and 16,000 pounds (5,500 and 7,300 kilograms). Their tusks reached up to 10 feet (3 meters) long.

Mammoths are related to African and Asian elephants and roamed vast stretches of North America and Eurasia until their extinction about 10,000 years ago.

The cause of extinction—whether climate change, hunting, or disease—is hotly debated.

Fisher and Rountrey believe that understanding the life history of individual mammoths may provide the insight needed to resolve this debate.

Tusk Tales

Prior to so-called tuskology, or the analysis of tusks, the lives of mammoths were studied by researching their modern elephant cousins, said Jeffrey Saunders, a mammoth specialist at the Illinois State Museum in Springfield.

"But as scientists, paleontologists, we are all aware that a mammoth or mastodon being extinct is not the same as a living form," he said.

The tusk analysis done by Fisher and his colleagues, Saunders added, is helping scientists understand the differences between living elephants and their extinct relatives.

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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