The Pteranodon kids are playing a game called "I'm the Biggest," which raises the question: how big is the biggest frog? Dad takes the kids on the Dinosaur Train to find the biggest frog ever, the legendary Beelzebufo. Once off the train, they have to take a river raft to find this illusive creature, but find him they do. The kids are surprised that Benny Beelzebufo isn't nearly as large (or mean) as they'd imagined, but he is definitely the biggest frog they've ever seen! Benny teaches the kids about his "sit-still-and-wait" hunting style and shows off his large, floating leaf "home." The Pteranodon family rides the "Night Train" all the way back to the Jurassic Period to visit their nocturnal friend, Vlad Volaticotherium, who tells them that he wants to take them caving! Buddy, Tiny, Shiny and Don don't even know what caving is, but they are soon having a great time seeing all the beautiful stalactites and stalagmites that have formed inside the cave. They also learn that it can be a lot of fun to hear your voice echo down the cave's long caverns!