Introduction to the Evolution of Birds

Chapter 1: Shared Characters - Birds and Reptiles
Birds are descended from reptilian ancestors. They arose nearly 200 million years ago, during the Mesozoic, the age of dinosaurs. In fact, birds are probably the closest living relatives of the dinosaurs! Chapter 1 shows the characteristics that birds and reptiles share.
Chapter 2: Unique Avian Characters
Despite their similarities to reptiles, birds are unique in a number of respects; their bodies have been shaped by the requirements for flight. This is why they are placed in a distinct class, Aves, within the Phylum Chordata. We present some of the major differences between birds and other vertebrates in Chapter 2