It's ambiguous, but I think "prehistoric" modifies the animal, like "pancake-shaped". If the title were "prehistoric-ocean dweller" then it modifies "ocean".

It's ambiguous, but I think "prehistoric" modifies the animal, like "pancake-shaped". If the title were "prehistoric-ocean dweller" then it modifies "ocean". The correct order[1] would be "prehistoric [age] pancake-shaped [shape] ocean dweller [proper?]". [1] https://www.gingersoftware.com/content/grammar-rules/adjectives/order-of-adjectives/ https://www.gingersoftware.com/content/grammar-rules/adjecti...