A new fossil stem group representative of Coliiformes (mousebirds) with a remarkable skull morphology is described from the late Oligocene of Germany. Oligocolius psittacocephalon sp. nov. for the first time preserves the skull of a post-Eocene fossil mousebird. This exhibits a combination of skull features unknown from any other bird and converges on the skull of parrots in that the beak is separated from the cranium by a marked nasofrontal hinge and in that the interorbital part of the frontal bones is very wide. In addition, the mandible of the new species exhibits long retroarticular processes, which are unexpected because unlike in other coliiform birds exhibiting this feature, the short beak was probably not used for probing in substrate. It is hypothesized that the retroarticular processes of O. psittacocephalon instead served for a particular wide and forceful opening of the beak. Eight large fruit stones are situated in the area of the digestive tract of the new species. Preservation of most of these in a well-delimited cluster in the region of the upper oesophagus suggests that, unlike in modern mousebirds, O. psittacocephalon had a crop. The new fossil shows that late Oligocene European stem group Coliiformes significantly differed from their extant relatives in morphology and probably also in feeding ecology.