Microcephale
"Microcephale" (meaning "tiny head") is the informal name of a genus of very small pachycephalosaurid dinosaur, otherwise known as the "North American dwarf species", which lived during the Late Cretaceous. Its fossils were found in the late Campanian-age Dinosaur Park Formation, in Alberta, Canada. Not much is known about this dinosaur, as it has not yet been fully described; it is therefore a nomen nudum. The fossils of "Microcephale", including tiny skull caps, were first mentioned by paleontologist Paul Sereno in 1997, in a list of pachycephalosaurids. These skull caps measure less than 5 cm (2 in) each. No potential species name was given.
A 2009 National Geographic documentary (Bizarre Dinosaurs) mentioned a tiny ("cat sized") pachycephalosaurid, called "Mycocephale" (meaning "mushroom head"). This is not a formally recognized genus and could be the same animal as "Microcephale".