Planocephalosaurus is an extinct genus of diapsid reptile belonging to the Order Sphenodontia. It was one of the first sphenodonts and bore a strong resemblance to the extant tuatara, albeit much smaller, at only 20 centimetres (7.9 in) in length. The main difference was that Planocephalosaurus's teeth were fused with the cartilage, unlike the tuatara's. The creature is presumed to have fed on large invertebrates and small vertebrates.

The Land Before Time

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In The Land Before Time V: The Mysterious Island, a Planocephalosaurus is briefly seen crawling on a rock in the scene after the Great Valley herd makes the decision to split up after a heated argument.