Diplocaulus (meaning "double caul") is an extinct genus of leponspondyl from the permain period of North America.Its most distinctive features were the long protrusions on the sides of its skull , giving the head a boomerang shape. Judging from its weak limbs and relatively short tail, it is presumed to have swum with an up-and-down movement of its body, not unlike cetaceans today. The wide head could have acted like a hydrofoil, helping the creature glide through the water. Another possibility is that the shape was defensive, since even a large predator would have a hard time trying to swallow a creature with such a wide head.
Available at Zoo Tycoon Wildlife.