It is a long, tall orange dinosaur with red stripes on its back and neck. It has short, smaller legs and red around its eyes.
While Ginger and the other lost kids chase SpongeBob through the lost and found, they pass through the lost world. SpongeBob rides on a Tylosaurus, while Ginger and the other lost kids ride in a box on a Tanystropheus' back.
At the end of the episode, when Squidward is lost in the lost world, a Tanystropheus can be seen walking around.