Its A Good Thing That Sea Urchins Didn’t Really Have to Wait Millions of Years For Their Self Sharpening Teeth

Posted by Chris Parker | May 9, 2009 0

Photo: The Department Heads Were Unamused

Sea urchin stories; we’ve got a million of them, but who doesn’t? According to “science” sea urchins developed their amazing self sharpening and ever sharp teeth over millions and millions of years. But why? Millions of years means millions of generations, so all those prior generations seemed to have done just fine. What was the impetus for sea urchins to devolope these self sharpening teeth and how did they give the improved sea urchins an advantage when millions of generations which had presumably gone before had done just fine without them?

The answer is, that they didn’t evolve over millions of years, because as it happens, the sea urchins need the self sharpening teeth to survive and they didn’t have time to “sit” around while they “evolved”. We would have had only about one generation of sea urchin in that case. The authors who studied these sea urchins can’t keep themsleves from using the word “designed” when describing this self sharpening system. Where there is design, there is a designer, my friends…

Forwarded by Arum (Thanks!)
Israeli Scientists: Sea Urchin Teeth Stay Sharp
by IsraelNN Staff, May 9, 2009

( Sea urchins dig themselves hiding holes in the limestone of the ocean floor using teeth that don’t go blunt. Weizmann Institute scientists have now revealed their secrets, which might give engineers insights into creating ever-sharp tools or mechanical parts.

The urchins dig holes to fit their globular bodies using their five teeth, which, like those of rodents, are ground down at the tip but continue to grow on the other end throughout the animals’ lives.

The amazing part, however, is that the teeth, which need to be harder and stronger than the rocky limestone being dug out, are themselves made almost entirely of calcite – the same calcite that makes up much of the limestone. How is this possible?

In a series of studies spanning more than a decade, Professors Steve Weiner and Lia Addadi of Weizmann’s Structural Biology Department have discovered that the urchins’ secret lies in a combination of ingenious design strategies.

The latest of these studies was reported recently in the Proceedings of the National Academy of Sciences (PNAS), USA.

The scientists found that the sea urchins’ teeth contain crystals of magnesium calcite, which are smaller, harder and denser than those of pure calcite; they are concentrated at the grinding tip of the tooth, particularly in the tip’s center, where the most force is being exerted in the course of grinding. The presence of magnesium calcite crystals acts like sand paper that helps to grind the rock down.

In the latest study, the researchers used X-ray photoelectron emission spectromicroscopy and other high-resolution imaging methods to uncover yet another amazing structural feature of sea urchin tooth design.

They found that all the crystalline elements that make up the tooth are aligned in two different arrays that are interlocked like the fingers of folded hands, just at the tip of the tooth where most of the wear occurs.

The scientists believe that interlocking produces a notched, serrated ridge resembling that of a carpenter’s file. This ridge is self-sharpening: as the tooth is being ground down, the crystalline layers break in such a way that the ridge always stays corrugated.

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