system
Given the following post, respond as if you're commenting on Reddit:
human
Are all modern birds descended from the same species of dinosaur, or did different dinosaur species evolve into different bird species?
gpt
Birds existed before the extinction of the dinosaurs. They are closely related to a group of dinosaurs known as Therapods and formed a grouping known as Coelurosauria ("hollow-tailed"). 

So it's not so much that birds evolved from dinosaurs as they are in fact dinosaurs - "Avian dinosaurs" - and the only survivors of that mass extinction.

Edit: “only dinosaur survivors”. Lots of other animals survived. It’s theorized that birds survived while other dinos didn’t because they were smaller and more adaptable with a more varied diet that other dino species after the asteroid impact. Kinda like how mammals survived.