data example in the software package r8s
(\url{http://ginger.ucdavis.edu/r8s/}).
}
-\seealso{
-\code{\link{chronogram}}, \code{\link{ratogram}}, \code{\link{NPRS.criterion}}.
-}
\references{
Sanderson, M. J. (1997) A nonparametric approach to estimating
divergence times in the absence of rate constancy. \emph{Molecular