Mastodons disappeared from Yukon before humans arrived: study

New research indicatesmastodons disappeared fromnorthern Canada long before humans crossed the Bering land bridge.

The results of new radiocarbon dating tests cast previous theories about the disappearance of mastodons in the North into doubt.

• Listen to an interview with Grant Zazula on CBC'sQuirks & Quarksthis week

"There's this prevailing idea that as soon as human hunters crossed the Beringland bridge they had sticks with spears and went across the continent and led everything to extinction," said GrantZazula, apaleontologistwith the Yukon government.

"When we did our radio carbon dates on all these mastodons from the Yukon and Alaska, we learned that they weren't even here by the time people showed up."

Mastodons were elephant-like mammals about three metres talland were covered in shaggy wool. They were herbivorous, mostly eating conifer twigs, and were distantly related to mammoths.

Zazula said the study shows mastodons, who were found during the ice age throughout most of southern North America, only came up north into Alaska and theYukon during warmer intervals.

"We had forests and it was nice and sunny, so it seems like American mastodons decided to come North on vacation," said Zazula.

"They travelled the AlaskaHighway to Alaska and Yukon but as soon as ice age conditions returned, their habitat was gone, was lost, and they were led to extinction here."

Previous radiocarbon dating estimated that the last mastodons in the Arctic disappeared around 18,000 years ago. Byremoving contamination from fossils before carbon dating them, the researchers found that the specimens from Beringiawere more than 50,000 years old, beyond the limits of carbon dating.

RossMacPhee, a curator at the American Museum of Natural History, also worked on the current study and says previous carbon dating work was incorrect because of the materials used to preserve the specimens.

He saidin some cases it shifted dates by tens of thousand of years.

"We have to now go back to the drawing board and think about whether or not we have lots of dates that are compromised in the same sort of way," he said.

Their paper was published today by Proceedings of the National Academy of Sciences.