Thanks to pack rats, however, these voles have not been forgotten.
In one Colorado cave, a pack rat collection of teeth and bones has yielded a layered slice of vole history between 600,000 and a million years ago, providing an unprecedented picture of how a species changes and evolves, and how its evolution is affected by climate change.
"Everything in the cave has been nicely preserved at a controlled temperature and humidity, like putting the stuff in a refrigerator for 750,000 years," said Tony Barnosky, a University of California, Berkeley, paleobiologist.
He and his former graduate student Chris J. Bell, now associate professor of geological sciences at the University of Texas at Austin, detail their study of fossil sagebrush voles, a rat-like rodent of the arid West, in a paper published online Oct. 21 in the Proceedings of the Royal Society B.
"This is the first study where we've actually taken a living species and looked back almost a million years at the population level to see how it changes through time," said Barnosky, an associate professor of integrative biology and associate curator at UC Berkeley's Museum of Paleontology.
"We've got a snapshot very early in the history of the species, around 750,000 years ago in the middle Pleistocene, in which we can trace details of what happens in time, plus a snapshot at 10,000 years and a modern snapshot." Together, these snapshots show very gradual change in the sagebrush vole, Lemmiscus curtatus, as the climate goes through one of many periodic cycles of glacial advance and retreat, with the original vole population coexisting and probably interbreeding with its evolving cousins.