The common ancestor of all dinosaurs was certainly terrestrial, so logically that means birds are the descendants of terrestrial dinosaurs. That was in the Trias. By the Jurassic, small tree-climbing theropods with feathers were gliding and soon starting to fly.
Also birds are not the descendants of terrestrial dinosaurs. They are dinosaurs, but their ancestors were also birds.
Are you saying that theropods weren’t terrestrial?
Just look at them, they are clearly extraterrestrial!
They are.
The common ancestor of all dinosaurs was certainly terrestrial, so logically that means birds are the descendants of terrestrial dinosaurs. That was in the Trias. By the Jurassic, small tree-climbing theropods with feathers were gliding and soon starting to fly.