Medusaceratops possessed a horny beak at the front of its skull and a prominent bony ruff at the rear

which lived in the late Cretaceous period

Polacanthus had more flexible armor

They lived during the Permian period

Kelenken Variant:Unprimed Medusaceratops possessed a horny beakKelenken (K. guillermoi `Terror Bird) is a genus of phorusrhacidae, an extinct group of large predatory birds that lived in the Middle Miocene to Neogene Epoch, about 15 million years ago, in what is now Argentina. Phororracids were large flightless birds with long hindlimbs, narrow pelvises, proportionately small wingspans, and huge skulls with a hooked beak and are thought to have been dominant land predators or scavengers in the Cenozoic. Kelenken