The mean absolute difference across all
nodes using these methods was approximately
5 Myr, with nearly all differences being older
in the multiple-calibration analysis than the
single-calibration analysis. This finding is potentially
significant given that the average bootstrap
estimate of standard errors was less than
these values. However, the difference at any
specific node was greater than 10 Myr for only
three of the nodes. One explanation for the
differences is that many of the minimum age
constraints used in our study (seven of 20) were
older than the ages inferred by Wikstr¨om et al.
(2001), pushing ages further back in time from
these constrained nodes.