Video: A chainsaw spiked with shark teeth

WEST PALM BEACH, FLORIDA—First there was the Sawzall, a reciprocating saw that is the go-to tool for tearing down walls and cutting up unwanted material. Now there’s the “Jawzall,” a tool invented by a Cornell University undergraduate and her colleagues to assess just how deadly different shark bites can be. Researchers have long known the puncture power of various shark teeth, but many sharks also shake their heads as they chow down on their prey, ripping its flesh. To learn more about such gnashing, the student mounted four to 10 teeth from a tiger shark (Galeocerdo cuvier), a sandbar shark (Carcharhinus plumbeus), a silky shark (C. falciformis), and a sixgill shark (Hexanchus griseus) onto separate sawing blades. Then she and her colleagues videotaped how well the teeth sliced through a dead salmon after six back-and-forth cuts. Tooth performance matched the lifestyle of the shark, she reported here today at the annual meeting of the Society for Integrative and Comparative Biology. The tiger shark’s serrated teeth, each with a large notch, were the most deadly, breaking the salmon’s spine quite readily in the six cuts: It feasts on turtles and crustaceans as well as softer bodied prey. In contrast, the sixgill’s large, coarsely serrated ivories performed the poorest, but that shark depends on carrion for food. The researchers used each Jawzall multiple times and found the teeth dulled quite quickly: After 12 back-and-forth cuts, teeth got through just 7% of the tissue cut on the first six cuts. Even though sharks grow new teeth every month, such rapid wear may limit how often they can eat.

(Video credit: Katherine Corn)