You Are My Best Friend (Tyrannosaurus Series) by Tatsuya Miyanishi
Once upon a time a violent, mean, selfish Tyrannosaurus roamed the land, and all the other animals feared him. One day, while chasing other animals, the Tyrannosaurus falls into the ocean. The Elasmosaurus, who lives in the sea, saves his life, and the Tyrannosaurus says “thank you” for the very first time. From that day, the land creature and the sea creature become best friends. The author, Tatsuya Miyanishi, delivers a heartwarming story about friendship with vivid, brightly colored illustrations and endearingly drawn characters.