ECHINOIDS IN 3D: UNDERSTANDING MECHANISMS THAT STRENGTHEN LIGHT-WEIGHT SKELETONS

The clypeasteroid echinoids are well-known from both the Recent and fossil record. Although sea urchins can feature thin-walled, light-weight skeletons, they often survive as fossils despite various taphonomic processes. Preservation potentials of echinoids often rely on the architecture of the calcareous skeleton. Plate interlocking mechanisms on different hierarchical levels and the presence of internal supports in clypeasteroids result in a test that is robust against external forces although supportive organic tissues are lacking. This analysis of the clypeasteroid skeleton focuses on the interlocking mechanisms as well as the arrangement and stereom distribution of internal supports system. The test of the minute clypeasteroid Echinocyamus pusillus has been analyzed using high-resolution x-ray micro-computed tomography, scanning electron microscopy and physical crushing tests for a detailed survey of the strengthening mechanisms. Results show that the plate’s edges feature numerus protrusions that interlock adjoining plates. On the microscopic level, trabecular protrusions additionally interlock the stereom when growing from one plate into the stereom interspace of a neighboring plate. The sutures where plates meet are thickened, thereby increasing the contact area between plates with the result that stress can be uniformly transferred along the entire suture, thus reducing local regions of high stress impact. The identified test strengthening principles provide the potential to improve technical multi-plated, light-weight and load-bearing structures for civil engineering which make them valuable role models for structural analyses.