Structure and Appearance
Birds are thought to have descended from Triassic Theropods which were already fairly bird-like.
They had a bipedal gait and a hollow bone structure similar to that of modern birds.
Scientific American, Feb. 1998
Archaeopteryx seems to be the intermediate form between reptiles and birds.
It is often cited as a classic example of a "missing link," and in the Victorian tradition of such important elements in traditional and gradualistic evolutionary progress, it is seen as "half reptile and half bird."