INVESTIGATING EUBLASTOID MORPHOLOGY THROUGH 3D GEOMETRIC MORPHOMETRICS

Over the past fifty years, traditional measurement and geometric morphometrics have been applied to fossil echinoderms to better understand the disparity in the large and diverse phylum. Previous work has shown that major clades in Echinodermata occupy different areas of morphospace and that some groups, particularly the eublastoids, are useful in considering long-term morphological change through time. Eublastoidea is an ideal group for morphometric analysis because their plate junctions are considered homologous and are easily identifiable on all species. Herein we investigate if the varying proportions of skeletal elements; oral/deltoid, radial, and basal plate circlets, that produce the gross thecal morphology are distinguishable in morphospace. This study will utilize over 50 specimens from the University of Michigan Museum of Paleontology that span all currently described families. These specimens have been reconstructed as 3D models utilizing photogrammetry. Then, 16 landmarks were placed on each specimen. The landmarks are an expansion on the work by Foote (1991) and are located at major plate boundaries in the A, B, and C rays and on the oral surface and basal triple plate junction. In addition to the fixed landmarks, a semilandmark mesh will be utilized to supplement the fixed landmarks in representing the gross thecal shape of the specimens. Finally, the Principal Component Analysis (PCA) was conducted. The resulting PCA depicts separation between previously described higher order groupings, which are retained. Additionally, groupings of superficially similar gross morphology (e.g., pyriform or globular) are apparent. Different morphological characters are mapped onto the PCA to consider homology and variation across the clade. Our findings provide a more detailed approach to understanding and describing eublastoid gross morphology.