The origin of birds has historically been a contentious topic within evolutionary biology. However, most researchers now believe birds are a group of theropod dinosaurs that evolved during the Mesozoic Era. A close relationship between birds and dinosaurs was first proposed in the nineteenth century after the discovery of the primitive bird Archaeopteryx in Germany. Birds share many unique skeletal features with dinosaurs. Moreover, fossils of more than twenty species of dinosaur have been collected with preserved feathers. There are even very small dinosaurs, such as Microraptor and An...