BRACHIOPOD SHAPE CHANGES ACROSS THE LATE ORDOVICIAN RICHMONDIAN INVASION: USING 3D GEOMETRIC MORPHOMETRICS TO ANALYZE MORPHOLOGICAL CHANGES THROUGH SPACE AND TIME

Invasive species can be detrimental to ecological communities. Analyzing effects of such invasion events through the fossil record may help us to understand the impacts of invasion events on ecosystems and aid in determining possible mitigation for extinction risks.

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 collected brachiopod fossils from the Late Ordovician along a depth gradient from offshore to shallow subtidal within the Cincinnati Arch from the C2 and C5 sequences. To measure changes in shell shape we used Structure-from-Motion (SfM), which uses 2-dimensional photographs taken of an object to reconstruct its 3-dimensional shape. 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).

Thus far, we have analyzed the 3-dimensional models of the genus Rafinesquina. Results show that Rafinesquina from the C2 sequence are inflated compared to the Rafenesquina from the C5 sequence, which show a flatter shape. We also compared shells across a depth gradient (deep versus shallow subtidal), which show that shallow and deep subtidal specimens in the C2 (pre-invasion) have distinct shapes, while the shell shapes from the C5 (post-invasion) are more homogeneous. Holland and Patzkwosky (2009) found similar results in community composition - pre-invasion communities were differentiated by depth but post-invasion communities were more mixed. Preliminary data is currently being processed for another genus, Cincinnatina.