Numerical taxonomy of fenestrate bryozoans: evaluation of methodologies and recognition of intraspecific variation

Abstract

Species-level taxonomy of fenestrate cryptostome bryozoans has been greatly advanced by a recent study of the fenestrate fauna of the Warsaw Formation (Osage–Meramecian) of the Mississippi Valley; subsequent quantitative analysis placed the earlier research on a sound statistical basis. Reproducibility of these results is tested here, and it is demonstrated that subsequent researchers can duplicate earlier data collection and results. The methodology is then extended in space and time to a second fenestrate faunule (Virgilian of east-central Kansas); morphs within two traditionally defined fenestrate species are successfully distinguished.Lithologic characteristics of the two Virgilian study units suggest differences in depositional environments between the horizons and therefore simple ecophenotypy and intraspecific variation cannot be dismissed. However, chamber dimensions, which provide the most sensitive characters for taxonomic discrimination, change in parallel for the two species, whereas exterior skeletal dimensions, which would presumably respond more readily to microenvironmental fluctuations, vary nonsystematically between populations. These results provide a starting point for the evaluation of morphologic change within fenestrates through stratigraphic and paleoenvironmental sequences. Cumulative data sets spanning long time intervals would allow evaluations of evolutionary histories among members of this important Paleozoic clade.