UB EARTH
SCIENCES

Methods

Methods for assessing congruence of age and clade data

Calculation of the three congruence metrics for age vs. clade comparisons, the stratigraphic completeness index, SCI (Huelsenbeck, 1994), the relative completeness index, RCI (Benton, 1994), and the gap excess ratio, GER (Wills, 1999). SCI is the ratio of consistent to inconsistent nodes in a cladogram. RCI is:

where MIG, minimum implied gap, or ghost range, and SRL is standard range length, the known fossil record. GER is:

,

where Gmin is the minimum possible sum of ghost ranges and Gmax the maximum, for any given distribution of origination dates. (a) The observed tree with SCI calculated according to the distribution of ranges in b. (b) The observed tree and observed distribution of stratigraphic range data, yielding an RCI of 66.0%. GER is derived from Gmin and Gmax values calculated in c and d. (c) The stratigraphic ranges from b rearranged on a pectinate tree to yield the smallest possible MIG or Gmin. (d) The stratigraphic ranges from b rearranged on a pectinate tree to yield the smallest possible MIG or Gmax.


References