A Northern Pocket Gopher can dig an amazing half a metre of tunnel through compacted clay soil in just 15 minutes. North American Beavers, along with humans, are the only mammals whose impact on their environment is so massive that it can be clearly seen with the naked eye from outer space. And there really are Narwhals - the single-tusked mammals that likely inspired the unicorn legend - living in the waters surrounding Greenland.

Learning about any of these mammals on their own brings out fascinating traits and stories. But when considered alongside the entire mammal population of...