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Calcite orientations and composition ranges within teeth across Echinoidea

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posted on 2020-05-04, 04:14 authored by Stuart R. Stock, Konstantin Ignatiev, Peter L. Lee, Jonathan D. Almer

Sea urchin’s teeth from four families of order Echinoida and from orders Temnopleuroida, Arbacioida and Cidaroida were studied with synchrotron X-ray diffraction. The high and very high Mg calcite phases of the teeth, i.e. the first and second stage mineral constituents, respectively, have the same crystallographic orientations. The co-orientation of first and second stage mineral, which the authors attribute to epitaxy, extends across the phylogenic width of the extant regular sea urchins and demonstrates that this is a primitive character of this group. The range of compositions Δx for the two phases of Ca1- xMgxCO3 is about 0.20 or greater and is consistent with a common biomineralization process.