A new eocene Chascacocolius-like mousebird (Aves: Coliiformes) with a remarkable gaping adaptation

A skull of a new species of mousebird (Aves: Coliiformes) is described from the Middle Eocene of Messel in Germany. Chascacocolius cacicirostris n. sp. is the fifth coliiform species described from the Messel deposits, and a further example of the remarkable similarity between the early Eocene avifaunas of North America and Europe. As for its much smaller North American counterpart, C. oscitans Houde & Olson, 1992, the new species has greatly elongated retroarticular processes on the mandible, which are an adaptation to gaping, i.e. opening of the bill in a substrate. The cranium and upper beak of Chascacocolius are seen for the first time in the new specimen; the latter shows a striking resemblance to the upper beak of some modern New World Blackbirds (Passeriformes: Icteridae). C. cacicirostris n. sp. thus provides another example of the diversification of early Tertiary Coliiformes, some taxa of which apparently occupied feeding niches that today are filled by songbirds (Passeriformes).