This is a simple request. There are a few mods out there that add dinosaurs, but none that immerse you in a world of dinosaurs. I'd love to play in a world where, instead of cows, sheep, zombies, and skeletons, it had venom-spitting dilophosaurus (skeletons), territorial pachycephalosaurus (zombies), velociraptors (baby zombies), docile ankylosaurus (cows), compys (chickens) and many more! Specifically, I think this would make an excellent mod for terrafirmacraft in particular, but normal minecraft could use it too.
That won't create a ballanced experience for minecraft. Not to mention the fact that none of the existing dinosaur mods actually cause dinosaurs to naturally spawn in the first place. This mod would need to provide exact equivalents to the existing mob drops. You know... like food, leather, feathers, and wool. The wool would be the tricky part, because no dinosaurs had fur. Just feathers. So a plant would have to take the sheep's place.