Paper No. 19
Presentation Time: 9:00 AM-6:00 PM
INTERNAL MORPHOLOGY OF BLASTOIDS (ECHINODERMATA): PEELS ARE STILL BETTER THAN DIGITAL IMAGING
WATERS, Johnny, Department of Geological and Environmental Sciences, Appalachian State University, 572 Rivers Street, Boone, NC 28608 and CREMINS, Devin, Department of Geology, Appalachian State University, 572 Rivers Street, Boone, NC 28608, watersja@appstate.edu
Visualizing internal structures in fossil taxa has long been a challenge in paleontology. Modern techniques include non-destructive imaging systems such as CT, microCT, and synchrotrons. High-resolution 2D images in combination with 3D reconstruction software can be transformed into detailed three-dimensional reconstructions. These systems work well when the internal structures being imaged and the material filling the voids have significant density contrast. These techniques are not as successful in specimens showing little density contrast between internal structures and the void filling. This is often the situation in fossil echinoderms, such as blastoids, which have thecae composed of calcite and voids filled by calcite mud or spar. Prior to the advent of modern imaging technologies, internal structures in fossils were visualized by serial sections and acetate peels. Although serial sectioning, often with acid etching, was time intensive and less precise than digital imaging, the technique did allow for the recognition of calcite structures preserved in voids filled with calcite.
The Naturalis Biodiversity Center in Leiden, Netherlands, houses a legacy collection of acetate peels from some 40 genera of blastoids. Most have never been published. Specimens mounted in epoxy disks were ground at 0.05 mm intervals through the oral area. Fifty to one hundred sections were produced for each taxon. We have been digitizing this archive with the intent of producing 3D models from the peels. At the moment, these peels produce higher resolution visualizations of the internal structures of blastoids than digital imaging techniques. We are able to recognize the following structures from our initial studies: the presence of gonopores and gonad sacs in Deltoblastus, previously unrecognized thecal canals and hydrospire orientations in Monoschizoblastus, and the partitioning of the internal thecal space into spaces separated by the internal prongs of deltoids in nucleocrinid genera. Although digital imaging techniques are the future, these peels are providing important morphological data critical to studies of blastoid phylogeny currently unavailable using current non-destructive imaging technology.
