From the Super Mario Wiki, the Mario encyclopedia
Mousersaurus Rex, also called Mouseraurus, is a giant red dinosaur that appears in the The Super Mario Bros. Super Show! episode "Quest for Pizza". This dinosaur has sunglasses like Mouser and resembles him. He helps Alley Koop throughout the episode. Although he is big and powerful, he is unable to speak. Additionally as a running gag, his foot keeps getting hurt throughout the episode.