@twinklecake Athough both birds and dinosaurs belong to the class Reptilia, if you by reptiles mean lizards and other such non-avian reptiles, then no, they are pretty far removed from dinosaurs(and consequently from birds). Even crocodilians, closest living relatives of birds/dinosaurs, only shared an ancestor 240 million years ago. And I assure you, when I see an emu or any similar bird, I AM reminded of raptors. And vice versa...
Fun fact, it wasn't the oxygen levels that made the dinosaurs so big(actually, today's levels are higher). Instead it was their more effective lungs(similar to birds), along with hollow bones and airsacks for lighter builds compared to same dimensions for mammals of similar size which gave them the edge...