Paleontology and the comparative method: ancestral node reconstructions versus observed node values.

Comparative methods are used to reconstruct ancestral node values for continuously varying traits. The confidence intervals (CIs) around such estimates may be wider than the range of tip data from which they are calculated. Without historical data with which to compare estimates, it is not clear whether such broad CIs reflect evolutionary lability or methodological imprecision. In this study, a fully resolved phylogeny of fossil carnivorans, in which observed samples are found not only at the tree tips but also along branches and at nodes, is used to compare observed ancestral node values with node estimates based on a Brownian motion model of evolution. As in previous studies, the CIs surrounding node estimates were wider than the range of tree tip values, but observed values fell well within them, reasonably close to the values predicted by comparative methods. Confidence intervals calculated using paleontological rate estimates were comparable to those calculated using only terminal taxa. This implies that evolution of at least some traits is conservative enough for node reconstruction techniques to be useful, despite their large standard errors. The Brownian motion model of evolutionary change was a good predictor of node values.