QUANTIFYING MORPHOLOGICAL CHANGES AMONG RAFINESQUINA (BRACHIOPODA) WITH 3D PHOTOGRAMMETRY

Articulated brachiopods are an abundant and diverse clade that dominated Paleozoic benthic ecosystems. They inhabited a wide range of water depths, thus they are an ideal group to study the relationship between morphology and ecology. We used 3D photogrammetry to analyze specimens of Rafinesquina collected across a depth gradient from the C5 stratigraphic sequence at Caesar Creek State Park, Ohio. Rafinesquina is very abundant across the sampled environmental gradient in the C5 so that environmental variability may be well represented. A 3D morphological study can help better quantify the morphological differences within the genus Rafinesquina and how morphological and ecological changes are related.

We developed a method that uses photogrammetry and structure for motion in order to distinguish the morphological variability of Rafinesquina specimens based on 3D digital models. Photogrammetry is a 3D technology that takes 2D photos of objects from different angles and aligns them in order to create a 3D model. We then expanded this method by moving it from extracted hand samples in the lab to rock slab samples in the field. These photographs were then exported into the photogrammetric software, Agisoft photoscan. Agisoft photoscan aligns these photos and creates a point cloud of the 3D specimen. The point clouds from multiple specimens were extracted and then analyzed using principle components analysis to identify how morphology changes across the environmental gradient.

Preliminary observations of 2D photos and 3D models are largely similar but there are some differences in shape or size across the C5 environmental gradient suggesting that morphological variation in shape and size among Rafinesquina specimens reflects adaptation to the environmental gradient. Rafinesquina specimens that were sampled from the distal deep subtidal environments seem to be more globose whereas Rafinesquina specimens sampled from the shallow subtidal and proximal deep subtidal environments were less globose.