Pachycephalosaurus

thick-headed lizard

• pachys · Greek · thick
• kephale · Greek · head
• sauros · Greek · lizard

The name combines Greek words for "thick", "head" and "lizard", referring to the animal's very thick, domed skull roof, which was made of solid bone and ringed with bony knobs and spikes. It was the largest known bone-headed dinosaur, and the group Pachycephalosauria is named after it.

Named by

Brown and Schlaikjer

Year named

1943

Period

Late Cretaceous

Stage

Maastrichtian

Found in

Hell Creek Formation, Montana, USA (also South Dakota and Wyoming)

Type species is P. wyomingensis, first described as Troodon wyomingensis by Gilmore in 1931 and moved to this genus in 1943. Known mostly from skulls, and some related genera such as Stygimoloch and Dracorex have been proposed by some researchers to be juvenile growth stages, though this is debated.