Recent analyses suggest that a few major shifts in diversification rate may be enough to explain most of the disparity in diversity among vertebrate lineages. At least one significant increase in diversification rate appears to have occurred within the birds; however, several nested lineages within birds have been identified as hyperdiverse by different studies. A clade containing the finches and relatives (within the avian order Passeriformes), including a large radiation endemic to the New World that comprises ~8% of all bird species, may be the true driver of this rate increase. Understanding the patterns and processes of diversification of this diverse lineage may go a long way toward explaining the apparently rapid diversification rates of both passerines and of birds as a whole. We present the first multilocus phylogenetic analyses of this endemic New World radiation of finch relatives that include sampling of all recognized genera, a relaxed molecular clock analysis of its divergence history, and an analysis of its broad-scale diversification patterns. These analyses recovered 5 major lineages traditionally recognized as avian families, but identified an additional 10 relatively ancient lineages worthy of recognition at the family level. Time-calibrated diversification analyses suggested that at least 3 of the 15 family-level lineages were significantly species poor given the entire group's background diversification rate, whereas at least one-the tanagers of family Thraupidae-appeared significantly more diverse. Lack of an age-diversity relationship within this clade suggests that, due to rapid initial speciation, it may have experienced density-dependent ecological limits on its overall diversity. Concatenation; concordance; congruence; diversification; gene tree; New World; Passeriformes.
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FUNDING This work was supported by collaborative NSF grants to the authors [DEB #0315218, #0315416, #0315469, and #0316092], as well as [IBN #0217817 to K.J.B.] ACKNOWLEDGMENTS This work would have been impossible without > 30 years worth of field collections made by dedicated researchers at institutions around the world. We most sincerely thank past contributors to and current stewards of collections at the following institutions that provided specimens used in this study: the American Museum of Natural History, Philadelphia Academy of Natural Sciences, Bell Museum of Natural History (University of Minnesota), Cornell University Museum of Vertebrates, Field Museum of Natural History, University of Kansas Natural History Museum, Louisiana State University Museum of Natural Science, Marjorie Barrick Museum (University of Nevada Las Vegas), Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Universidad Nacional Autónoma de México, Facultad de Ciencias, Museo de Zoologia “Alfonso L. Herrera”, University of California, Berkeley Museum of Vertebrate Zoology, National Museum of Natural History (Smithsonian Institution), San Diego State University Museum of Biodiversity,Smithsonian Tropical Research Institute, Burke Museum of Natural History and Culture (University of Washington), Peabody Museum (Yale University), and the University of Copenhagen’s Zoological Museum. We particularly acknowledge the generosity and patience of Robb Brumfield, Van Remsen, Fred Sheldon, and Donna Dittmann at LSU, without whose assistance a work this comprehensive could never have been done. Thanks to Mark Miller and Wayne Pfeiffer, who assisted us in some analyses using resources of the CIPRES Science Gateway. This work benefitted from the comments of Matthew Dufort, Sharon Jansa, and two anonymous reviewers.