We thank Fangliang He, Andrew Martin, Richard Norris, Klaus Rohde, and John Wilkins for their insightful comments and suggestions. A.P.A. was supported as a Postdoctoral Associate at the National Center for Ecological Analysis and Synthesis, a center funded by National Science Foundation Grant DEB-0072909, and the University of California, Santa Barbara. V.M.S. was supported by National Institutes of Health Grant 1 P50 GM68763-02 through the Bauer Center for Genomics Research.
Footnotes
Abbreviations: CI, confidence interval; FO, first occurrence; Ma, mega-annum; SSU rDNA, small subunit rRNA-encoding DNA.
To whom correspondence may be addressed. E-mail: drewa@nceas.ucsb.edu
or jhbrown@unm.edu
Freely available online through the PNAS open access option.
Author contributions: A.P.A., J.F.G., and J.H.B. designed research; A.P.A. and J.F.G. performed research; A.P.A. and V.M.S. contributed new reagents/analytic tools; A.P.A. analyzed data; and A.P.A., J.F.G., V.M.S., and J.H.B. wrote the paper.
Conflict of interest statement: No conflicts declared.
© 2006 by The National Academy of Sciences of the USA