The extinct amphibian with a boomerang-shaped skull was Diplocaulus. Its skull had two unusually long, backward-pointing projections that spread from the sides of the head, creating one of the most distinctive silhouettes in the Permian fossil record.
Diplocaulus was a lepospondyl amphibian, not a reptile or mammal-like synapsid. It lived from the Late Carboniferous into the Late Permian, with fossils known mainly from North America and Africa. The animal had a stocky, salamander-like body and could reach about 1 metre in length. Paleontologists have proposed several functions for its broad skull, including improved stability while swimming or an adaptation that helped it glide through water, but its exact purpose remains debated.
The name means “double stalk,” referring to the paired skull projections. A frequent mix-up is Dimetrodon, another famous Permian animal from North America. Dimetrodon had a tall sail on its back and was a synapsid, whereas Diplocaulus was an amphibian whose unusual feature was on its head. Some Diplocaulus fossils were even found in burrows associated with attacks by Dimetrodon.