title: Dating the diversification of the major lineages of Passeriformes (Aves).
abstract: BACKGROUND
  The avian Order Passeriformes is an enormously species-rich group, which comprises almost 60% of all living bird species. This diverse order is believed to have originated before the break-up of Gondwana in the late Cretaceous. However, previous molecular dating studies have relied heavily on the geological split between New Zealand and Antarctica, assumed to have occurred 85-82 Mya, for calibrating the molecular clock and might thus be circular in their argument.
  
  
  RESULTS
  This study provides a time-scale for the evolution of the major clades of passerines using seven nuclear markers, five taxonomically well-determined passerine fossils, and an updated interpretation of the New Zealand split from Antarctica 85-52 Mya in a Bayesian relaxed-clock approach. We also assess how different interpretations of the New Zealand-Antarctica vicariance event influence our age estimates. Our results suggest that the diversification of Passeriformes began in the late Cretaceous or early Cenozoic. Removing the root calibration for the New Zealand-Antarctica vicariance event (85-52 Mya) dramatically increases the 95% credibility intervals and leads to unrealistically old age estimates. We assess the individual characteristics of the seven nuclear genes analyzed in our study. Our analyses provide estimates of divergence times for the major groups of passerines, which can be used as secondary calibration points in future molecular studies.
  
  
  CONCLUSIONS
  Our analysis takes recent paleontological and geological findings into account and provides the best estimate of the passerine evolutionary time-scale currently available. This time-scale provides a temporal framework for further biogeographical, ecological, and co-evolutionary studies of the largest bird radiation, and adds to the growing support for a Cretaceous origin of Passeriformes.
authors.affiliation: Department of Zoology, Swedish Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden. per.ericson@nrm.se.
authors.forename: Per G P
authors.initials: PG
authors.lastname: Ericson
authors.forename: Seraina
authors.initials: S
authors.lastname: Klopfstein
authors.forename: Martin
authors.initials: M
authors.lastname: Irestedt
authors.forename: Jacqueline M T
authors.initials: JM
authors.lastname: Nguyen
authors.forename: Johan A A
authors.initials: JA
authors.lastname: Nylander
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000235:genetics; D019143:Evolution, Molecular; D005580:Fossils; D005819:Genetic Markers; D009520:New Zealand; D046109:Passeriformes / Q000145:classification / Q000235:genetics*; D010802:Phylogeny
chemical_list: D030161:Avian Proteins; D005819:Genetic Markers