When I was young birds were thought to be descended from dinosaurian ancestors and therefore distantly related to true dinosaurs but in recent years a lot has changed. We now know that birds are actually dinosaurs, though in disguise if you will. We know that birds rose from a close relation of the mighty T-Rex we all remember fondly from our youth. If you look at the scaly feet and the beak of a bird like a pigeon up close you won't find this too hard to swallow.
There's a very nice and detailed article on the excellent Smithsonian site about our current understanding on the origins of birds with particular attention that to that item which was long thought to be a bird exclusive: feathers. Turns out many dinosaur lineages had featherlike structures, not just the therapods (T-rex and family).
What's even more amazing is that we now can find out which colours these feathers had, which was deemed impossible in my youth.
Sinosauropteryx was even more stunning. Zhang found that the filaments running down its back and tail must have made the dinosaur look like an orange-and-white-striped barber pole.
Ah science, you continue to delight me.
Read the entire thing if you have a spare 15 minutes.
Dinosaurs' Living Descendants