Forum. Stratigraphic Fit to Phylogenies: A Proposed Solution

Three measures intended to assess the fit of stratigraphic age to the fossil record have been suggested previously: the Spearman Rank Correlation (SRC), the Stratigraphic Consistency Index (SCI) and the Relative Completeness Index (RCI). The original formulation of SRC is intractable to all but pectinate trees and the corrective pruning procedure that circumvents this precludes whole-tree estimates of fit. SCI, though it has been claimed otherwise, is strongly biased by tree shape, particularly as one adds more information. RCI is a measure of the amount of gap in the fossil record but has awkward consequences for evolutionary biology when it is maximized. A new approach, the Manhattan Stratigraphic Measure, uses the Manhattan distance between stratigraphic ages to determine fit to a tree. It is not biased by tree shape, it is sensitive to the magnitude of age discrepancy and there is an obvious significance test.