Recent availability of stratigraphically continuous and hiatus-free sequences of pelagic sediment in deep sea cores have encouraged biostratigraphers to interpret lineages of oceanic microfossils from a viewpoint of gradual phyletic evolution. A few taxa do show anagenetic evolution, but the excellent stratigraphic record obtained from deep sea coring reveals that the overwhelming majority of species show only cladogenetic evolution with no gradual speciation. Biostratigraphers nevertheless persist in recognizing ancestral-descendant relations whenever possible, and arbitrary limits must therefore be applied when an evolving lineage is divided. This typological practice may be good biostratigraphy, but it is poor biosystematics.

Phyletic biohorizons and lineage zones are explicitly defined and recognized by evolutionary criteria. For interpretation, these horizons and zones must rely on notions of phyletic gradualism and ancestor-descendant relations. These notions must rely on an evolutionary theory to allow their inference. However, biostratigraphy should not rely on evolutionary theory since biostratigraphy is the means by which we correlate strata to test evolutionary hypotheses about patterns of fossil phylogeny.

For good biostratigraphic practice, evolutionary species should be recognized as single lineages without arbitrary and typological subdivision. Biosystematic analysis should begin with a cladogenetic analysis which infers taxon relations from characters exhibiting shared derived similarities. Classification should immediately follow to preserve the monophyletic relations of the clades. This system results in universal and timeless taxonomic hypotheses which are potentially falsifiable and thus scientifically testable. A biozonation based on such taxa is independent of evolutionary theory. Untestable assumptions and ad hoc hypotheses of ancestral-descendant relations and gradual speciation, such as must be used to recognize phyletic biohorizons and lineage zones, are unnecessary.

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