GEOMETRIC MORPHOMETRICS OF CINCINNETINA (BRACHIOPODA) ACROSS THE RICHMONDIAN INVASION EVENT IN THE LATE ORDOVICIAN
Here, we investigate the 3-dimensional morphological diversity of brachiopods across the Richmondian Invasion approximately 450 Mya. During this event, new taxa invaded the Cincinnati area, dramatically changing community composition. We digitally collected brachiopod fossils from the Late Ordovician along a depth gradient from offshore to shallow subtidal in the Cincinnati Arch from before (C2 sequence) and after (C5 sequence) the Richmondian Invasion event. To measure changes in shell shape we used Structure-from-Motion to reconstruct its 3-dimensional shape from 2-dimensional photographs. We photographed specimens in the field in a 360 degree arc (approximately 24 photos per specimen) and used the software ‘Agisoft Metashape’ to build 3D models of each brachiopod. We exported these models into R and used the package ‘geomorph’ to generate a set of semi-landmarks across the surface of the shells. To determine shape changes, we used a Procrustes transformation and a Principal Components Analysis (PCA).
Two specific genera were analyzed: Rafinesquina and Cincinnetina. Results for Rafinesquina show that pre-invasion specimens vary in shape between shallow and deep subtidal environments and post-invasion specimens become more similar in shape.
Preliminary results on Cincinnetina show that there is an decrease in morphological disparity post-invasion. This has been linked to increased extinction susceptibility in other studies (Kolbe etc al., 2011). Overall similarities between Rafinesquina and Cincinnetina Principal Components Analyses show that there are significant changes in shape across the Richmondian Invasion and post-invasion specimens showing a more square shape.