Appearance event ordination
Appearance event ordination or AEO is a scientific method for biochronology through the ordering of the appearance of fossil mammal genera by multivariate analysis, using conjunctional (overlapping) and disconjunctional (nonoverlapping) range distributions in large sets of data. Process AEO is based on faunal overlap and stratigraphic superposition to derive a best-fit sequence of first and last appearance events. Step 1 The first step is to translate patterns of overlap and superposition into pairwise first-before-last statements. The wolf species Canis edwardii and Canis armbrusteri are used as example taxa for the following patterns. Each statement means C. edwardii, for example, must have first appeared before C. armbusteri last appeared. This is true whenever either (1) C. edwardii and C. armbrusteri have been found together in at least one nontime-averaged fossil collection, or (2) C. edwardii is found lower in at least one lithostratigraphic section than C. armbrusteri. Step 2 A multivariate ordination algorithm is applied to derive a first-pass, hypothesized sequence of first and last appearances. The minimal constraint on this sequence is that if there is an observed, real-world C. edwardii before C. armbrusteri statement for any pair of taxa, the hypothesized event sequence must replicate it. Then, the program