pachycephalosaurian

pach·y·ceph·a·lo·saur·i·an

 (păk′ĭ-sĕf′ə-lə-sôr′ē-ən)
n.
Any of various herbivorous bipedal ornithischian dinosaurs of the group Pachycephalosauria of the Cretaceous Period, having a very thick skull and a beaked mouth. Also called pachycephalosaur.

[From New Latin Pachycephalosauria, group name, from Pachycephalosaurus, type genus; see pachycephalosaurus.]

pach′y·ceph′a·lo·saur′i·an adj.