Multicharacter Chronological Clustering in a Sequence of Fossil Sticklebacks

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Abstract
Chronological clustering of morphotypes, based on five characters, detected morphological discontinuities in a stratigraphic sequence of the fossil stickleback Gasterosteus doryssus. Discontinuities that were not detected analyzing individual characters became apparent, and different discontinuities depend on changes in the frequencies of different sets of morphotypes. However, recognition of discontinuities between a group and neighboring groups of samples depended strongly on existing group structure. The results of this analysis generally were consistent with conclusions of a previous study using single characters, which indicated that patterns of chronological variation within the lineage are diverse. Care must be taken in interpreting the results of this chronological-clustering technique because the results depend strongly on criteria for formation of morphotypes, but the technique is useful to detect discontinuities of multicharacter change within biostratigraphic sequences.