AVIAN HISTORICAL BIOGEOGRAPHY: INTEGRATING FOSSILS, PHYLOGENY, AND ECOLOGICAL NICHE MODELING TO INVESTIGATE DRAMATIC CENOZOIC RANGE SHIFTS

Earth’s lower latitudes boast the majority of extant avian species-level and higher-order diversity, with many deeply diverging clades restricted to vestiges of Gondwana. However, paleontological analyses reveal that many avian crown clades with restricted extant distributions had stem group relatives occupying very different parts of the world. Here, we corroborate this pattern with new phylogenetic evidence on the enigmatic fossil bird Foro panarium, from the early Eocene (Wasatchian) of Wyoming. Our phylogenetic analyses support F. panarium as a stem turaco (Aves: Pan-Musophagiformes), a clade that is presently endemic to sub-Saharan Africa. To investigate environmental mechanisms underlying extreme shifts in avian biogeographic ranges throughout the Cenozoic, we used multivariate environmental modeling to estimate the temperature and precipitation tolerances of every extant avian clade at the ordinal level whose classic ‘Gondwanan’ distributions, like that of the turaco total group, were challenged by the discovery of fossil stem member relatives in Northern Hemisphere Eocene lagerstätten. We examined the correspondence between present-day tolerances of these clades and their paleo-distributions as derived from model projections onto past Eocene climate conditions. We find evidence for probable distributional changes that occurred congruently across clades, coinciding with cooling in the Oligocene that eventually restricted lineages to subtropical and tropical belts of Africa, South America, and Australasia. These new biogeographic analyses reveal the fossil record as vital for accurately inferring the complex historical biogeography of crown birds across geological timescales, and emphasize the role played by global cooling at the Eocene-Oligocene boundary in structuring the higher-level taxonomic composition of modern avifaunas.