This is why people want to grow up to be scientists. To find out more about the morphological differences in shark teeth and how this affects the way different sharks hunt and kill, scientists have developed a novel way to simulate a realistic shark bite: Glue shark teeth onto an electric saw.
Humans have long been thrilled by sharks’ toothy grins. Luckily, these days, due to changing attitudes and understanding, we are more likely to be fascinated by them rather than afraid, although it seems there is still so much we don’t know.
There are more than 400 different species of shark, and each of them has uniquely shaped teeth: triangular, sharp and serrated, and thin and spiky. Despite being aware of this, scientists have had trouble getting up close and personal with a shark while it’s chomping away to see just how these different shaped teeth actually cut and bite through tissue.
Researchers at the University of Washington decided to study why shark teeth are shaped differently and what biological advantages each shape has, by testing how they perform under as realistic conditions as possible. This is where the glue and saw come in.
"When you have all these different tooth shapes, there should be some functional reason. That issue was fundamentally troubling to me," said senior author Adam Summers, a UW professor of biology and of aquatic and fishery sciences, in a statement. "It seemed likely what we were missing is that sharks move when they eat."
As sharks often shake their heads as they bite, Summers and his team realized that finding a way to replicate how the different teeth perform when moving from side to side would be crucial to their study.
To simulate this movement, they affixed three different types of shark teeth – tiger, silky, and bluntnose sixgill – to a reciprocating power saw and had it slice through thick chunks of Alaskan salmon at the same speed a shark shakes its head during an attack.
"Sure enough, when we cut through salmon, different teeth cut differently," Summers said. "We found a way to distinguish between this huge morphological difference we see among shark teeth in nature."
High-speed video of the cutting apparatus using a blade with teeth from a silky shark (Carcharhinus falciformis) on salmon. University of Washington
The results, published in the journal Royal Society Open Science, demonstrated that shark teeth differences come down to how best to devour their prey depending on how that prey’s tissue behaves.
Both the tiger and silky sharks’ teeth dulled relatively quickly over a few tests. As their known prey includes middle-sized marine mammals, turtles, and birds, all of which require sharp teeth to bite into pieces, the researchers think this could mean these sharks replace old dull teeth with sharp new ones every time they kill prey.
The bluntnose sixgill teeth, on the other hand, didn’t cut as well but also didn’t dull as quickly as the others, which could mean they don't need to slice as much as they swallow their prey whole.
"There's this tradeoff between sharpness and longevity of the tooth edge," Summers explained. "It looks like some sharks must replace their teeth more often, giving them a consistently sharp tool."
The team believes this is the first study of its kind to mimic the way sharks hunt and kill. "It is really important to test biological materials at strain rates that are high enough to mimic how the predator and prey tissues would actually behave in real life," said co-author Stacy Farina, a postdoctoral researcher at Harvard University and an adjunct lecturer at Shoals Marine Laboratory.
"We asked ourselves, how do we safely and effectively move these teeth back and forth quickly?" Farina added. "The quick and dirty way was, glue them onto a power saw. It was a simple solution to a complicated problem."
