If, however, we were to use Sinornis, Iberomesornis, Cathyornis , and other Mesozoic birds but excluded Archie, these derived features would still be there. Archaeopteryx shares derived features with modern birds, although it lacks many advanced features of later birds. I think you can see where I'm going with this one. Suffice it to say, nowadays we really have a pretty good morphological sequence of fairly well-preserved animals linking Archaeopteryx securely with the modern birds. Hence, if Archaeopteryx was not a bird, then neither is a house sparrow.
Birds are fairly unusual critters.
And practically every skeletal peculiarity in birds can be traced to non-avian dinosaurs. Non-archaeopterygian birds also show distinctly maniraptoran characters, including the carpal block, deep coracoids, large sterna, and the form of the hand. I particularly like the illustration by Bakker in The Dinosaur Heresies of the hands of a hoatzin hatchling, Archaeopteryx , and Deinonychus . Check it out. The above were public posts to the dinosaur mailing list.