Phylogenetically vetted and stratigraphically constrained fossil calibrations within Aves

Abstract

Understanding the timing of the crown radiation of birds is a major goal of avian molecular systematists and paleontologists. Despite the availability of ever-larger molecular datasets and increasingly sophisticated methods for phylogeny reconstruction and divergence time estimation, relatively little attention has been paid to outlining and applying fossil calibrations. As the avian fossil record has become better sampled, and more extinct taxa have been incorporated into a phylogenetic framework, the potential for this record to serve as a powerful source of temporal data for divergence dating analyses has increased. Nonetheless, the desire for abundant calibrations must be balanced by careful vetting of candidate fossils, especially given the prevalence of inaccurate fossil calibrations in the recent past. In this contribution, we provide seven phylogenetically vetted fossil calibrations for major divergences within crown Aves representing the splits between (1) Anatoidea, (2) Sphenisciformes, (3) Coracioidea, (4) Apodidae, (5) Coliiformes, (6) Psittaciformes, and (7) Upupiformes, and the respective extant sister taxon for each of these clades. Each calibration is based an individual specimen, which maintains the clearest possible chain of inference for converting the relevant stratigraphic horizon to a numerical date. Minimum ages for each fossil are tightly constrained and incorporate associated dating errors, and the distributions of younger fossils from the clades of interest are summarized to provide a starting point for workers interested in estimating confidence intervals or outlining prior age distribution curves. Daniel Ksepka. National Evolutionary Synthesis Center, Durham, North Carolina, 27706, USA. ksepka@nescent.org Current address: Bruce Museum, Greenwich, Connecticut 06830, USA Julia Clarke. Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas 78713, USA. julia_clarke@jsg.utexas.edu