Well over a million years ago, in what is now the southern Yukon, a tiny vole perished.

Its body lay withering into a skeleton near an ancient stream. At some point, the stream flowed over the site of the tiny rodent's death, gathered up its remains, and swept them away.

Eventually, the delicate bones and teeth settled to the streambed, along with a burden of sediment and the remains of other animals caught up in the flow. And there they stayed, buried by successive layers of silt, ash, rock, gravel, and soil deposited by millennia of water, wind, and ice.

They lay unnoticed until 1988 when geologists Lionel Jackson and Brent Ward spotted the jumble of animal fossils while exploring evidence of past volcanic action in the Yukon and Pelly river valleys near Fort Selkirk.

Jackson and Ward were primarily interested in using the layers of volcanic basalt, ash, and intervening sediment to construct a timeline for the geology of the Fort Selkirk area. However, the fossils themselves attracted the attention of John Storer, the Yukon government's staff paleontologist.

"I actually started to learn about paleontology with small mammals," he says, explaining that he studied under the world's leading fossil rodent expert. "Small mammals turn out to be very useful to work on."

The short life spans of small mammals mean that the species change and evolve quickly. Tracking minute changes in things like the teeth of voles allows paleontologists to build up a picture of their development through time and compare it with fossil findings in other locations.

Very little is left of the vole that died so long ago, but there's enough to tell a story that has implications beyond the Yukon.

Storer analysed the dimensions and shapes of tiny teeth sifted out of the glacial till in the ancient streambed and identified their owner as Microtus deceitensis, an extinct meadow vole named for its first recorded identification in a fossil deposit at Cape Deceit on the Alaskan shore of the Bering Strait.

Storer's study has done more than identify an ancient resident of the Yukon. He has also managed to narrow down the time range during which the little meadow vole lived and deduce something about the conditions in which it lived.

Narrowing down the time range takes us back to the work of Lionel Jackson, who first spotted the fossil deposit. The area around Fort Selkirk was once actively volcanic, and Jackson has used the evidence of volcanism to help date layers of rock and sediment.

The group of fossils containing the vole teeth was found in a layer of wind-blown glacial dust, or loess, indicating that glaciers were not far away in time or space.

Below it was a layer of basalt, solidified rock that once flowed from an active volcano. Analysis of the basalt has placed its age at about 1.8 million years.

Above the fossil group was a layer of volcanic ash called the Fort Selkirk tephra, the result of a different volcanic eruption. It has been dated at about 1.48 million years old.

Therefore, the age of the fossil group is older than the Fort Selkirk tephra and younger than the underlying basalt, or between about 1.5 and 1.7 million years, Storer says.

Dating the Fort Selkirk vole also allows Storer to suggest a date for the original Cape Deceit vole. Small differences in the structure of the teeth indicate that the Fort Selkirk vole is more advanced, he says, and therefore lived a little later than the Cape Deceit vole.

The little meadow vole was not alone in its Fort Selkirk grave. With it and a number of its relatives were the remains of a dozen other species of animals, from caribou and bats to rabbits and lemmings. Knowing when the vole lived gives Storer an idea of when the other animals lived, and the mix of species begins to give him a picture of the conditions of the time.

It's still a broad picture, he warns. The animal remains were deposited in a jumble, some distance from where they died, "and a lot can happen between death and deposition."

Nevertheless, Storer is pleased with the amount of information gleaned from the deposit. And there's another deposit nearby.

"It's enough to go on for the time being, but more things could be done with the other locality," he says.

For more information about Yukon creatures of long ago, go to the website of the Yukon Beringia Interpretive Centre at www.beringia.com or visit the Centre itself. For information about paleontology in the Yukon, contact John Storer at john.storer@gov.yk.ca.