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The University of Tennessee

Earth and Planetary Sciences

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The skeleton of an echinoderm is made from tens to tens of thousands of individual ossicles (typically called plates), each a single crystal of high magnesium calcite. Typically, these plates articulate to each other with soft connective tissue that rapidly decomposes upon the death of the animal. Consequently, most fossil echinoderms are preserved in the rock record only as sand sized particles that are of little use to paleontologists.

However, recent investigations into echinoderm microstructure reveals that important information can be recovered from even the smallest disarticulated pieces. Echinoderms have a unique skeletal microstructure called stereom that manifests itself as a network of interconnected holes. In life, this stereom mesh is filled with living tissue, and different types of stereom are indicative of the type of living tissue that penetrates the plate. To this end, I am currently examining stereom in several extinct echinoderm lineages to reconstruct the soft tissue structure and reconstruct the organism's functional morphology.

SEM photograph of a sea star ambulacral plate. Note the variation in the stereom showing labyrinthic (unorganized mesh) stereom on the right side of the plate, and coarse fascicular (rod like) stereom midway along the upper surface.

SEM photograph of a sea star integument plate. This plate shows rectilinear (box-like) stereom characteristic of the ectoderm.

SEM potograph of a sea star spine. Note the even labyrinthic stereom and the small, imperforate spinelets.


Colin Sumrall

Department of Earth and Planetary Sciences
1412 Circle Drive
Knoxville, TN 37996-1410
Phone: (865) 974-0400

Research and Teaching Activities