Many scientists now see the birds as deriving from a suborder of the order Saurischia or alternatively as a subdivision of theropod dinosaurs. One claimant to be the first bird is Protoavis. The fossils of this animal (the name means means 'ancestral bird') come from the Triassic period, and are 225 million years old. Discovered by Dr Sankar Chatterjee, the partial remains of Protoavis have been identified by other paleontologists as more dinosaur-like than bird-like, and a healthy debate exists as to whether or not Protoavis is a true ancestor of the birds.

The first bird that we 'safely' know about was probably Archaeopteryx, which lived 150 million years ago. Archaeopteryx means 'ancient wing', and this animal may be the most famous fossil find of all time. Archaeopteryx was larger than a crow and had sharp teeth, a long bony tail and three clawed fingers. Although Archaeopteryx could probably fly a few feet, it is not thought to have been capable of flight like a true bird. Archaeopteryx lived in the Late Jurassic period, and specimens have been found in limestone deposits in Bavaria, West Germany. The first specimen was discovered in 1861, and since then six skeletons have been found.

The same area of China that yielded fossils of Sinosauropteryx and Caudipteryx has also been the site of several early bird discoveries. Protarchaeopteryx is a 120 million year old bird that appears even more primitive than Archaeopteryx - it probably glided rather than flapped its wings. Confuciusornis ('sacred Confucius bird'), also dated to the early Cretaceous period, was probably one of the first birds that could fly well. This bird had wings similar to those of Archaeopteryx, but had lighter bones and a shorter tail that may have improved its flying skills. Confuciusornis is the earliest known bird with a toothless beak.