Add Yahoo as a preferred source to see more of our stories on Google. It's difficult to consider birds similar enough to humans or dogs to think of them as mammals, though. So, are birds mammals? If ...

Part 1. The historical perspective -- 1. Introduction -- 2. The history of mammals [animals] -- 3. The early radiations -- 4. The Edentata -- 5. The Pholidota -- 6. Conclusions concerning the early ...