Achelousaurus has two large spikes on the frill, and udults have lumpy mounds for both brow and nose horns.Etymology: Greek Achelous (mythical river god) + Greek sauros (lizard) "horneri" (for Jack Horner, paleontologist). Holotype: MOR 485 Referred specimens: MOR 591, MOR 571. Achelousaurus horneri had well developed supraorbital and nasal bosses similar to those of Pachyrhinosaurus, although the nasal boss was slightly smaller and the supraorbital bosses weres lightly larger. Both may have been used for intraspecific combat. It also possesed twin parietal spikes, a feature it shared with Einiosaurus.