Diplocaulus (meaning "double stalk") was not a dinosaur but an early amphibian, now extinct. It was distinguished by its boomerang-shaped head which was formed by two elongated 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.
Its unusually-shaped head may have made it difficult for predators, such as Eryops, to swallow it. Its head also may have been used as a hydrofoil, letting Diplocaulus swim against the current. It may have used its tail to help it swim.
Diplocaulus probably ate insects and fish.
Like all amphibians, it had to live near the water since amphibian eggs have no shells and must be laid in the water (or in very damp areas) or they will dry out and die. Also, it lost its gills as an adult.
When Diplocaulus Lived
Diplocaulus lived from the late Carboniferous to the late Permian period (roughly 270 million years ago), long before the dinosaurs evolved.
Diplocaulus was a tetrapod, an amphibian, a labyrinthodont, a lepospondyl, and a nectridian.
Diplocaulus fossils have been found in Texas, USA, North America.