GEOMETRIC MORPHOMETRIC ANALYSIS OF THE SB-C ELEMENTS OF DAPSILODUS OBLIQUICOSTATUS

Dapsilodus obliquicostatus (Branson and Mehl, 1933) is a species of coniform conodont that exhibits distinct morphological variability in the S_b-c element although other elements of the apparatus appear identical. Some S_b-c elements resemble the type material, which has an equilateral basal cavity, while other samples appear to exhibit a significant curvature in the outline of the basal cavity and a recurved cusp. This change in form can be visualized using landmark-based geometric morphometric analyses, i.e. principal component and canonical variate analyses. These tests will quantifiably characterize the shapes of the morphotypes of D. obliquicostatus. This study will determine if the morphological variability observed in D. obliquicostatus is indicative of a single species with variably curved basal cavities and cusps, or if the curved form represents a discrete cryptic species that has been mislabeled as D. obliquicostatus. The samples used for this experiment were collected from the St. Clair Formation (Silurian; Sheinwoodian and Homerian) in the Schlamer Core #1. Independent age control based on standard conodont biostratigraphy shows that the curved form ranges younger stratigraphically than the regular form. More samples are needed from additional sections, but if the curved morphotype can be identified as a discrete species that exhibits a limited age range, then this research opens up the possibility of using the new species as a rough index fossil for Homerian intervals that lack platform elements. Furthermore, no previous studies have used geometric morphometrics to analyze coniform conodont elements. This work will be a case study for applying geometric morphometric analysis to similar coniform conodont species.