Buddy and his Pteranodon family journey under the sea to visit their underwater friends in a brand-new invention, the Dinosaur Train Submarine! They visit Otto Ophthalmosaurus and explore a sea cave. Shoshana Shonosaurus takes them deep down into the ocean to fish. While enjoying some time on the beach, Buddy and the Pteranodon family see baby sea turtles hatch! Episodes include: Otto Ophthalmosaurus - When the Pteranodon family takes the Dinosaur Train under the sea to visit their friend Elmer Elasmosaurus, they learn that the Elasmosaurus family is going away from the station to follow their food, the fish. Buddy wants to follow, but the train tunnel doesn't go that way - so the Conductor decides to take the family in a brand-new invention, the Dinosaur Train Submarine! On their journey, they meet a marine reptile called Otto Ophthalmosaurus, who guides the submarine deeper than it's ever been, and even helps them find their way out of a sea cave. Shoshana Shonosaurus - The Pteranodon family goes under the sea again, to ride the Dinosaur Train Submarine - this time they go to meet Shoshana Shonisaurus, an enormous marine reptile that's something between a dolphin and a whale. Since Shoshana loves to dive down very deep, Shiny has a problem with following her down to the bottom of the sea. Shoshana kindly helps Shiny get over her fear of diving deep. Maisie Mosasaurus - The Pteranodon family goes back underwater in the Dinosaur Train Submarine and meet Maisie and Marvin Mosasaurus, a daughter and father who are huge, fast-swimming lizards with flippers. Maisie and Shiny bond when they discover neither likes to go down deep in the water. The Pteranodons and Mosasaurus have a great time up near the ocean's surface, each family showing the other how they hunt and catch fish to eat.A Sea Turtle Tale - The Pteranodon family is on the beach watching small eggs hatch and baby Archelon turtles emerge, and start to swim away. The family and Mr. Conductor get into the Dinosaur Train Submarine and follow the baby Archelons who discover their own facts of nature - that their mother doesn't stay with them after they're born, and that they will grow up to be giant-sized sea turtles.