Sea Urchin Tooth Design: An “All-Calcite” Polycrystalline Reinforced Fiber Composite for Grinding Rocks


  • We thank Talmon Arad, Eugenia Klein, and Ronit Popovitz-Biro for their help with different aspects of the electron microscopy; Prof. Muki Spiegel, Sharon Marziano, and David Krugoliac of the Israel Oceanographic and Limnological Research company for providing fresh sea urchins; Panagiotis Karkanas (Ephoreia of Palaeoanthropology and Speleology, Greece) for the naturally growing sea urchins; and Holger Pfäff (Surface, Hückelhoven, Germany) for helpful discussions. The study was supported by the Minerva Foundation and the Helen & Milton A. Kimmelman Center for Biomolecular Structure & Assembly. L.A. is the incumbent of the Dorothy and Patrick Gorman professorial chair of Biological Ultrastructure, and S.W. is the incumbent of the Dr. Walter and Dr. Trude Burchardt professorial chair of Structural Biology.


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A convenient tooth. Here we investigate how the different kinds of calcite crystals in a sea urchin tooth (left) work together as an effective grinding tool. The polycrystalline matrix has a higher elastic modulus and hardness than the single crystals, yet both work together to produce a flat grinding surface (right).