By analyzing these layers and the chemicals present in the tusk, researchers can estimate how many years a mammoth lived, its diet, whether or not it was nutritionally stressed, and if it was nursing from its mother.
"However, a problem with using layers to reconstruct mammoth life histories is that tusk tips, which contain the layers formed early in life, are often broken or worn away. This means that the earliest part of the record may be missing," Rountrey told Animal Planet News.
To bridge between juvenile and adult tusks, the researchers looked for an event that might be preserved in both, such as weaning.
They analyzed the left tusk of a young woolly mammoth (
Mammuthus primigenius) from Wrangel Island, in northeastern Siberia. The tusk had a relatively intact tip.
In order to determine when the young mammoth was weaned, the researchers examined the tusk's carbon and nitrogen.
"Milk has a higher proportion of heavy nitrogen and a lower proportion of heavy carbon than the plants a mammoth might eat, and these differences show up in the tusk of a nursing calf," says Rountrey.
Results indicated that weaning took place gradually over at least four years, and possibly six or more years.
"That compares with an average of about five years for African elephants at weaning," said team leader Daniel Fisher, professor of geological sciences, ecology and evolutionary biology at University of Michigan.
At least until its third year of life, the young Siberian mammoth calf was feeding on high-fat "early milk," the result of the mother drawing on her stored fat and protein resources.
The milk would have provided the calf with a large portion of its calories in the harsh arctic conditions, ensuring steady growth rates even when there wasn't much food available, said the researchers.
"Finally we have direct information on the lives of mammoth calves and the maternal investment in terms of milk input," Fisher told Animal Planet News.
According to Larry Agenbroad, a leading mammoth expert at Northern Arizona University, the study "documents life and death of extinct proboscideans in a totally new, accurate methodology, allowing even more accurate comparisons with living elephants."
"Fisher and his team have extended our knowledge of mammoth-mastodon life histories, time of death and now nursing, to levels we previously could have never dreamed of," Agenbroad told Animal Planet News.
Name: Woolly Mammoth (
Mammuthus primigenius)
Primary Classification: Proboscidea (Elephants)
Location: Northern Europe, Siberia and North America.
Habitat: Cold, dry grasslands, open tundra and steppe.
Diet: Low tundra vegetation.
Size: Up to 11.5 ft in length, 10 ft in height and 10,000 lbs in weight.
Description: Dark brown to black in color; long, dense hair and underfur; long, curved tusks; high domed head; humped, sloping back.
Cool Facts: Adults ate up to 400 pounds of vegetation daily. Its tusks could grow to 16 feet. It is among the largest land mammals of the past 2 million years.
Conservation Status: Extinct
