Diplocaulus

Diplocaulus (meaning "double stalk") was an early amphibian, now extinct. It had a boomerang-shaped head formed by two long bones at the back of the head. It had four short legs, and a short, flattened tail. It was about 3 feet (1 m) long. 

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References

Other websites
Real Skull 

category:Fossils
category:Amphibians