DELINEATING SPECIES OF RAFINESQUINA IN THE TYPE CINCINNATIAN (ORDOVICIAN): GEOMETRIC AND MULTIVARIATE MORPHOMETRIC APPROACHES

Fossils of the Cincinnati, Ohio region have been intensively studied for well over a century. During this interval, numerous species and subspecies of the brachiopod genus Rafinesquina have been described. These taxa were erected using a typological species concept, and most modern paleontologists agree that the lineage has been over-split. Yet there is little scientific consensus about how population variation in morphology relates to biologically meaningful species in this clade. In this study, we apply multivariate statistical procedures to test whether morphometrics can be used to differentiate biologically meaningful species.

The great abundance of available fossils makes the genus Rafinesquina an ideal subject on which to test the efficacy of morphometric methods of species delineation. Dorsal valve exteriors of nine previously named species were analyzed. Outline data were captured using ImageJ. General Procrustes Analysis was performed on both data sets. Principal Component Analysis was used to rotate the data onto major axes. Pairwise comparisons and a Permutational ANOVA were then used to identify discrete species morphologies within morphospace. Binary and continuous morphological characters were selected for use in Detrended Correspondence analysis, and Principal Coordinates Analysis. Analyses were conducted using the R programming language and software environment.

Based on results of this study, multivariate morphometrics is a successful method for identifying distinct species of Rafinesquina in the study region and two-dimensional outline based geometric morphometrics is not. These multivariate morphometric analyses can provide the basis for differentiating population-level variation from species-level distinctions required for future systematic revision of the genus.