The early E ocene birds of the M essel fossil site: a 48 million‐year‐old bird community adds a temporal perspective to the evolution of tropical avifaunas

Birds play an important role in studies addressing the diversity and species richness of tropical ecosystems, but because of the poor avian fossil record in all extant tropical regions, a temporal perspective is mainly provided by divergence dates derived from calibrated molecular analyses. Tropical ecosystems were, however, widespread in the N orthern H emisphere during the early C enozoic, and the early E ocene G erman fossil site M essel in particular has yielded a rich avian fossil record. The M essel avifauna is characterized by a considerable number of flightless birds, as well as a high diversity of aerial insectivores and the absence of large arboreal birds. With about 70 currently known species in 42 named genus‐level and at least 39 family‐level taxa, it approaches extant tropical biotas in terms of species richness and taxonomic diversity. With regard to its taxonomic composition and presumed ecological characteristics, the M essel avifauna is more similar to the N eotropics, M adagascar, and N ew G uinea than to tropical forests in continental A frica and A sia. Because the former regions were geographically isolated during most of the C enozoic, their characteristics may be due to the absence of biotic factors, especially those related to the diversification of placental mammals, which impacted tropical avifaunas in A frica and A sia. The crown groups of most avian taxa that already existed in early E ocene forests are species‐poor. This does not support the hypothesis that the antiquity of tropical ecosystems is key to the diversity of tropical avifaunas, and suggests that high diversification rates may be of greater significance.