It is a bird because it had feathers. However, it retained many dinosaurian characters which are not found in modern birds, at the same time, having certain characters found in birds but not in dinosaurs.
Archaeopteryx is an example of a trasition between dinosaur to bird.
It lived in the Late Jurassic period, about 150 million years ago. It was the size of a jet fighter. It lived at what is now Big Bend, Texas, near the end of the Cretaceous Period, and went extinct at the same time as the big dinosaurs. For millions of years both pterosaurs and birds existed on Earth, but now pterosaurs are gone and birds fill the skies. Quetzalcoatlus may have eaten carrion like a vulture, or perhaps it plucked mollusks from the mud of river floodplains with its beak.