Achelousaurus

What it was like

Achelousaurus was a plant-eating dinosaur that walked on four legs and carried a large head with a beak at the front, much like other ceratopsians. It grew to about 6 meters (20 feet) long. Where many of its relatives had horns above the eyes and on the nose, Achelousaurus instead had rough, thickened bosses in those spots.

A bony frill extended from the back of its skull, with a pair of curved spikes at the edge. The bosses were probably covered in a tough layer of keratin in life, and some researchers think animals may have used them to butt heads or to show off to rivals.

Its world

Achelousaurus lived from about 84 to 72 million years ago, during the Late Cretaceous, in what is now Montana in the United States. Its fossils come from the Two Medicine Formation.

It shared its world with other plant eaters such as Maiasaura and Einiosaurus, as well as predators including Daspletosaurus and Troodon. Armored Euoplocephalus and fast-moving Saurornitholestes also lived in the same region.

How it was found

Sampson named Achelousaurus in 1994, based on fossils collected in Montana. Only two finds are known, mostly skull material from animals at different ages, from juveniles to adults. Its closest relatives include Styracosaurus, Pachyrhinosaurus, and Triceratops, and some researchers think Achelousaurus may represent a stage between horned and bossed ceratopsians, though this idea is debated.