Quite complex and innovative teeth, it turns out.
Sea urchins hide in DIY limestone holes.
They have five teeth which, like those of rats, grow throughout the animals’ life.
So far so normal (the five bit is only normal if you are echinoderm, of course).
These teeth are almost entirely calcite – the same mineral that makes up much of the limestone.
However, natural Innovation One it that they are better suited to their task by a line of small harder magnesium calcite crystals running up the centre, held in place by a matrix calcite crystals.
X-ray photoelectron emission spectromicroscopy amongst other techniques has revealed Innovation Two: the crystalline elements that make up the tooth are aligned in two different interdigitated arrays.
The scientists (see below) believe that interlocking produces a notched serrated ridge that is self-sharpening: as the tooth is ground down, the crystalline layers break in such a way that the ridge always stays corrugated.
The research was a collaboration between: the Weizmann Institute of Science in Israel, the University of Wisconsin, the Max Planck Institute of Colloids and Interfaces in Germany, and the Museum National D’Histoire Naturelle in France.
It was reported in the Proceedings of the National Academy of Sciences.
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(Picture – By walknboston under Creative Coomons Attribution Licence)