700,000 YEARS 700,000 : SCIENCE CANADIAN MASTER ESSAY

DURING the Klondike gold rush at the turn of the 20th century, prospectors learned that there was more than just gold in the hills of Yukon, a territory in Canada.

There were fossils - lots and lots of fossils. These were spectacular finds, too : mountains of woolly mammoth tusks and the bones of saber-toothed cats and extinct giant bison.

The icy rock faces also contained the tunnels and dens of prehistoric ground squirrels, which were filled with thousands of frozen pellets of ancient poop.

Many dens remained uninterrupted, perhaps because droppings are in less demand than mammoth skulls. But leaving these droppings on ice for another century meant that the technology to analyze fossilized DNA had progressed.

In a new study, published in the journal Nature Communications, researchers have revealed a startling connection between the rodents and their massive neighbors. The ground squirrels' fossilized feces contained DNA from woolly mammoths, saber-toothed cats and bison, suggesting that the squirrels were eating meat from the large animals.

The ancient poop, and the info dump it facilitated, is an example of 'amazing preservation, recording these ecosystems over hundreds of thousands of years,'' said Tyler Murchie, a paleontologist in British Columbia and the study's lead author.

WHY is it so hard to get genetic data from fossils? DNA degrades over time, and many fossils undergo a transformation in which their original organic molecules are replaced by mineral deposits.

That means that most fossil feces, or coprolites, have more in common with a rock than with a fresh pile of droppings. But because the Klondike region's ancient squirrel dens remained frozen and sealed for around 700,000 years, the contents including the sections used as latrines - were still preserved.

So Dr. Murchie's colleagues went ahead and excavated hundreds of pellets of frozen feces from the dens and brought them back to the Ancient DNA Center at McMaster University in Ontario.

There the scientists used chemicals to break down the proteins and minerals in the coprolites to isolate any remaining DNA.

Dr. Murchie said that even the oldest samples gave off a telltale odor during this chemical digestion. '' I did not think that these would smell anymore, especially when you're talking about 700,000-year-old poop, '' he said.

'' It was intense.''

But the result of genetic testing revealed a bigger surprise : After comparing the DNA sequences with known species, matches were found for plants, insects and small mammals, as well as for woolly mammoths, caribou, wolves, cougars and wild horses.

It's possible the squirrels ate these other animal droppings, but it's more likely the squirrels were scavenging on carcasses.

The idea of a squirrel feasting on flesh might seem jarring, but most rodents aren't picky. '' If there's a lot of seeds and nuts and other plant materials around, they'll eat that,'' Dr. Murchie said.

'' But if there isn't that, or if there happens to be a carcass nearby, they'll definitely eat that carcass.''

!WOW! thanks Kate Golembiewski.