In 1973, a teacher named Joan Hodgins took her students on a hike near Whitehorse in Canada's Yukon Territory. In the process, she made history for this chilly region. While exploring the tailings left behind by a now-defunct copper mine, Hodgins and her students stumbled across a few fragments of fossils -- bits and pieces of what seemed to be teeth alongside pieces of bone. The ancient fragments of teeth were so small and in such bad shape that "most paleontologists may not have picked them up," said Jaelyn Eberle, a curator of fossil vertebrates at the University of Colorado...