I disagree. I think Archeopteryx Lithographica
is an excellent example of the transition from dinosaur to bird. What's so different about it from other birds is how oh so dinosaurian it is. It really does look like a dinosaur as well as a bird.
Archeopteryx did not have a beak. It has a proper jaw with proper teeth. This is a very unbirdlike characteristic, and a very dinosaur-like characteristic. It also has a bony tail; this is again not very birdlike and is very dinosaur-like.
Archeopteryx has features of both birds and dinosaurs. It can be classified as just a bird (by some scientists and not others), but it still is a species representative of the transition from dinosaur to bird.