New data on the anatomy and palaeobiology of sandcoleid mousebirds (Aves, Coliiformes) from the early Eocene of Messel

The Sandcoleidae are stem group representatives of the Coliiformes (mousebirds). These birds are among the most abundant medium-sized arboreal birds in some early and middle Eocene fossil sites of Europe and North America, and they are particularly well represented in the German locality Messel. Here, new sandcoleid fossils from Messel are reported. Most of these are tentatively assigned to Eoglaucidium pallas, which is the only named European sandcoleid species, but one specimen is likely to represent a new, unnamed species. Another fossil exhibits exceptionally well-preserved feather remains, which show that the tail of sandcoleids was not as greatly elongated and stiffened as that of extant mousebirds (Coliidae). It is hypothesised that these differences in the tail morphology of sandcoleids and coliids may have been due to changes in the habitual perching posture, which occurred early in the evolutionary history of the Coliidae.