While still rolling down the river on the Dinosaur Train Riverboat, Grandpa Pteranodon tells Buddy about the Legend of Admiral Globidens – a HUGE Mososaur that supposedly lives on the river, but no one has ever seen. Buddy enlists Dad and Tiny’s help to look for Admiral Globidens, but they can’t seem to find him. Does Admiral Globidens really exist, or is he just a figment of someone’s imagination?