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Turtle clades divergence dates



From: Ben Creisler
bcreisler@gmail.com


In the new issue of Journal of Paleontology:


Walter G. Joyce, James F. Parham, Tyler R. Lyson, Rachel C. M.
Warnock, and Philip C. J. Donoghue (2013)
A Divergence Dating Analysis of Turtles Using Fossil Calibrations: An
Example of Best Practices.
Journal of Paleontology 87(4):612-634.
doi: http://dx.doi.org/10.1666/12-149
http://www.bioone.org/doi/abs/10.1666/12-149

Turtles have served as a model system for molecular divergence dating
studies using fossil calibrations. However, because some parts of the
fossil record of turtles are very well known, divergence age estimates
from molecular phylogenies often do not differ greatly from those
observed directly from the fossil record alone. Also, the phylogenetic
position and age of turtle fossil calibrations used in previous
studies have not been adequately justified. We provide the first
explicitly justified minimum and soft maximum age constraints on 22
clades of turtles following best practice protocols. Using these data
we undertook a Bayesian relaxed molecular clock analysis establishing
a timescale for the evolution of crown Testudines that we exploit in
attempting to address evolutionary questions that cannot be resolved
with fossils alone. Some of these questions, such as whether the
turtle crown originated in the Triassic or Jurassic, cannot be
resolved by our analysis. However, our results generate novel
age-of-origination estimates for clades within crown Testudines.
Finally, we compare our fossil calibrations and posterior age
estimates to those from other studies, revealing substantial
differences in results and interpretation.