Chasmosaurus was discovered by Lawrence Lambe in 1898. He discovered part of the neck frill. However, Lambe believed he had found another species of Monoclonius, which he named Monoclonius belli. In 1913, Charles Sternberg and his sons found more Chasmosaurus skulls, that were actually complete. Chasmosaurus was finally described as a new genus, and named Chasmosaurus by Lawrence Lambe in 1914.
Chasmosaurus had a very large neck frill. To make it lighter, the bone had holes in it, like most Ceratopsians. Only Triceratops had a solid frill. This bone was covered in a layer of skin, and around the edge of the frill were several small studs. On its head, it had three horns, like Triceratops, and a beak for snapping tough plant matter.