Why do you think they are called terrible and marvelous Dinosaur?

Terrible part, easy, marvelous, not so easy.

They called dinosaurs stuff like "Terrible Claw" and stuff like that because of the fierce, killer claws and teeth the carnivores with Terrible in their name had, like Deinonochus' Claws!

I think they call dinosaurs marvelous (in the name) because they might have been graceful, amazing, or just plain beutiful.