Possible cerebellar folding within early maniraptorans. (A) Endocast of Citipati osmolskae, an oviraptorosaur theropod, with cerebellar folds indicated by arrows in the inset. (B) Horizontal CT slice through the folded cerebellum of a living bird, Melanerpes aurifrons (Golden-fronted woodpecker). Slice orientation indicated on skull in lower left corner. (C) Horizontal CT slice through the cerebellum of C. osmolskae. (D) The same horizontal slice shown in (C) with the cerebellar folds outlined in blue. Black dotted line indicates hypothesized fold, but it is unclear due to poor resolution.