Bird or dinosaur? Birds are the only living animals with feathers, but did you know that some dinosaurs had feathers too? Unlike birds, these creatures had teeth and long, bony tails. They ranged in size from the feisty Microraptor, which was small enough to hold in your hand -- if you weren't afraid of its sharp teeth -- to the Beipiaosaurus, which was over seven feet long. Paleontologists learned about these creatures, which lived approximately 145 million years ago, by studying fossils.
