Shark teeth are the longest-lasting piece of the animal - their bones are cartilage and usually decompose quickly when a shark dies. But despite the longevity of shark teeth, marine biologists were unable to draw substantial conclusions about the animal because there was no good way to look at teeth structure.
That's all changed, using the technology of X-ray computed tomography, otherwise known as CT ("cat") scans.
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At Cornell University evolutionary biologist Willy Bemis, graduate student Josh Moyer and director of the Micro CT facility, Mark Riccio, decided to use CT scanner and the latest imaging software to look deep into the structure of shark's teeth. The images showed structural patterns that weren't visible before and allowed them to compare lots of teeth, answering questions about a sharks' growth, development and evolutionary history - some of which had been lingering for at least a century.
"The thing is we can compare fossil and living shark's teeth," Bemis told Discovery News. "Because the technology is now cheaper, we can survey a large number of species in ways that were impractical in the past."
And shark teeth they do have: there are specimens that have been sitting around on shelves for years. One big advantage of the CT scan is that it's possible to see the teeth forming in the (dead) shark's head, without taking apart the specimen. The CT scan also shows an individual tooth's internal structure, which also changes as a shark ages. That reveals a lot about a shark's development, and doesn't require a scientist to slice up each tooth individually to peer inside.
CT scans were once a cumbersome business. Not only were the machines huge, but the computers and software needed to tease out images were expensive and the calculations for generating the images took a lot of time. But in the last decade, a combination of small CT machines and fast computers has made this kind of research feasible.
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Before CT scans, the definitive work on shark teeth was Bernhard Peyer's, "Comparative Odontology" in 1968. Peyer didn't have CT scanners, though, so he couldn't study how shark's teeth mineralize - a basic, open question is exactly what that process looks like over time. Nor could he get a good look at the vasculature of the tooth. "There's been relatively little attention in the intervening time," Bemis said. He hopes to change that.
Image: Cornell University / Josh Moyer