However, unlike modern mouse birds the skull and beak of Oligocolius closely resembles those of parrots, and appears to be specialised for a distinct lifestyle not found in living mousebirds.

The first specimen of Oligocolius was discovered in a clay pit at Frauenweiler, near Wiesloch in Germany, dated to the Rupelian approximately 32 million years ago during the early Oligocene from which its name derives.

The specimen was described and named by palaeontologist Gerald Mayr in 2000, included much of the skeleton, but was disarticulated and missing its skull, as well as most of both its left wing and foot.

[1] A second specimen was later described by Mayr in 2013 from the late Oligocene (24.7 Ma) lagerstätte in Enspel (an ancient maar lake) near Bad Marienberg, Germany.

However, the combination of the long retroarticular process and the nasofrontal hinge is only found in parrots and Oligocolius, suggesting they share a similar degree of cranial kinesis.

[2] It is unknown if Oligocolius had the characteristic long tail feathers of other mousebirds, however O. brevitarsus has a very well-developed pygostyle to suggest so.

[1] The presence of a crop in Oligocolius implies that it was feeding on fruits and vegetation that was tougher to digest than those in the diet of living mousebirds.