Final answer:
Fossilized skin impressions are known for all of the listed dinosaur groups: ornithopods, theropods, and ceratopsians. Archaeopteryx is the oldest known 'dinosaur-bird' fossil.
Step-by-step explanation:
Fossilized skin impressions are known for D. all of the above: A. ornithopods, B. theropods, C. ceratopsians. These dinosaur groups have all provided evidence of skin impressions which help paleontologists understand more about their appearance and texture of their integument.
Specifically addressing the student question, the oldest known fossil of a "dinosaur-bird" is that of Archaeopteryx, and it is currently understood that modern birds (Aves) evolved from theropod dinosaurs, specifically the maniraptoran theropods, not the Ornithischia, which had a pelvis superficially similar to birds.