what made it a bird and not a flying dinosaur? Was it because ti had feathers? If it flew and had feathers it was no longer a dinosaur, but a bird?
Orly, sometimes you ask questions that are far beyond the scope of an answer we can reasonably compose on SciForums. I suggest you read the Wikipedia articles on the
origin of birds and the
evolution of birds, and, for good measure, plain old
birds. This subject is far more complicated than you give it credit for, and there's also a bit of controversy involved. Your questions are so oversimplified that they condense out some of the key issues in the relationship between birds and dinosaurs. There's no easy way to answer them because they're not the right questions.
I've heard scientists answer, in exasperation, "Birds
are dinosaurs." That statement is not false, it's just not complete.
Ostriches are surely birds. They're members of an order called the
ratites. The ratites have no "keel" on their sternum (breastbone) so there's nothing to anchor powerful wing muscles to. Even if they had appropriate-sized wings, they couldn't fly. Besides, if a 350-pound ostrich could fly, how large do you suppose its wings would have to be, considering that the condor, weighing a mere 25 pounds, has a ten-foot wingspan?
The other eight species of ratites are, in order of size, the emu, the cassowary, the rhea, and the five kiwis.
At 45mph, the ostrich is the fastest animal that runs on two legs.
Oh BTW, penguins don't fly either.