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Curr Biol. 2018 Jun 4;28(11):1825-1831.e2. doi: 10.1016/j.cub.2018.04.062. Epub 2018 May 24.

Early Evolution of Modern Birds Structured by Global Forest Collapse at the End-Cretaceous Mass Extinction.

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Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK. Electronic address:
Department of Paleobiology MRC-121, National Museum of Natural History, Smithsonian Institution, 10(th) Street and Constitution Avenue NW, Washington, DC 20560-0121, USA.
Department of Ecology & Evolutionary Biology, Cornell University, 215 Tower Road, Ithaca, NY 14853, USA.
Integrated Research Center, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL 60605, USA.
Department of Geosciences, University of Rhode Island, 9 East Alumni Avenue, Kingston, RI 02881, USA.
Department of Earth Sciences, Denver Museum of Nature and Science, 2001 Colorado Boulevard, Denver, CO 80205, USA.
Department of Palaeobiology, Swedish Museum of Natural History, Svante Arrhenius Väg 9, 104 05 Stockholm, Sweden.
Department of Geology & Geophysics, Yale University 210 Whitney Avenue, New Haven, CT 06511, USA.


The fossil record and recent molecular phylogenies support an extraordinary early-Cenozoic radiation of crown birds (Neornithes) after the Cretaceous-Paleogene (K-Pg) mass extinction [1-3]. However, questions remain regarding the mechanisms underlying the survival of the deepest lineages within crown birds across the K-Pg boundary, particularly since this global catastrophe eliminated even the closest stem-group relatives of Neornithes [4]. Here, ancestral state reconstructions of neornithine ecology reveal a strong bias toward taxa exhibiting predominantly non-arboreal lifestyles across the K-Pg, with multiple convergent transitions toward predominantly arboreal ecologies later in the Paleocene and Eocene. By contrast, ecomorphological inferences indicate predominantly arboreal lifestyles among enantiornithines, the most diverse and widespread Mesozoic avialans [5-7]. Global paleobotanical and palynological data show that the K-Pg Chicxulub impact triggered widespread destruction of forests [8, 9]. We suggest that ecological filtering due to the temporary loss of significant plant cover across the K-Pg boundary selected against any flying dinosaurs (Avialae [10]) committed to arboreal ecologies, resulting in a predominantly non-arboreal post-extinction neornithine avifauna composed of total-clade Palaeognathae, Galloanserae, and terrestrial total-clade Neoaves that rapidly diversified into the broad range of avian ecologies familiar today. The explanation proposed here provides a unifying hypothesis for the K-Pg-associated mass extinction of arboreal stem birds, as well as for the post-K-Pg radiation of arboreal crown birds. It also provides a baseline hypothesis to be further refined pending the discovery of additional neornithine fossils from the Latest Cretaceous and earliest Paleogene.


K-Pg; ancestral states; birds; ecological selectivity; mass extinction; paleobotany

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