title: Low ecological disparity in Early Cretaceous birds.
abstract: Ecological divergence is thought to be coupled with evolutionary radiations, yet the strength of this coupling is unclear. When birds diversified ecologically has received much less attention than their hotly debated crown divergence time. Here, we quantify how accurately skeletal morphology can predict ecology in living and extinct birds, and show that the earliest known assemblage of birds (=pygostylians) from the Jehol Biota (≈125 Ma) was substantially impoverished ecologically. The Jehol avifauna has few representatives of highly preservable ecomorphs (e.g. aquatic forms) and a notable lack of ecomorphological overlap with the pterosaur assemblage (e.g. no large or aerially foraging pygostylians). Comparisons of the Jehol functional diversity with modern and subfossil avian assemblages show that taphonomic bias alone cannot explain the ecomorphological impoverishment. However, evolutionary simulations suggest that the constrained ecological diversity of the Early Cretaceous pygostylians is consistent with what is expected from a relatively young radiation. Regardless of the proximate biological explanation, the anomalously low functional diversity of the Jehol birds is evidence both for ecological vacancies in Cretaceous ecosystems, which were subsequently filled by the radiation of crown Aves, and for discordance between taxonomic richness and ecological diversity in the best-known Mesozoic ecosystem.
authors.affiliation: Committee on Evolutionary Biology, The University of Chicago, Chicago, IL 60637, USA Department of Science and Education, The Field Museum of Natural History, Chicago, IL 60615, USA mitchelljs@uchicago.edu.
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Mitchell
authors.affiliation: Department of Science and Education, The Field Museum of Natural History, Chicago, IL 60615, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Makovicky
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000033:anatomy & histology* / Q000502:physiology*; D001842:Bone and Bones / Q000033:anatomy & histology; D017753:Ecosystem; D005247:Feeding Behavior; D005580:Fossils / Q000033:anatomy & histology*
keywords: Jehol Biota; bird evolution; functional diversity; palaeoecology