Kenaley’s computer-generated image of a viperfish (left) and the resulting 3D-printed robot. Image: Christopher Kenaley / Gary Wayne Gilbert

In the ecosystem of the deep sea, the shiny, gunmetal-colored dragonfish are like “the lions of the Serengeti,” says Christopher Kenaley, biology assistant professor of the practice. At depths of between 660 feet and two miles—a dark and impoverished region that some scientists call the twilight zone—these fish, amounting to roughly 200 species, are the alpha predators. With long fangs and the ability to open their mouths more than 100 degrees (the human “gape angle” is closer to 40 degrees), members of the dragonfish family (Stomiidae) can capture prey greater than half their size. Even so, and as with most creatures of the truly deep, their size is small, with a head an inch high and a skinny, tubular body six to 12 inches long.

Given their habitat’s challenges to human exploration, scientists have never recorded dragonfish feeding. Do they use their needle-sharp fangs to impale their quarry (including the narrow six-inch silver-scaled lanternfish that Kenaley calls “the cookies of the deep sea”)? Can they generate sufficient force with their very slender jaws to penetrate the scales of prey? With funding from the National Science Foundation, Kenaley, whose specialty is vertebrate biomechanics and physiology, has been developing models of a particularly fierce-looking species of dragonfish known as the viperfish, searching for answers.

Kenaley and two undergraduate assistants created the two models above—on the left, a digital 3D simulation, on the right a 3D-printed skeleton—in his Higgins Hall laboratory. To produce the color rendering of the viperfish head, they bathed a specimen from the collection of Harvard’s Museum of Comparative Zoology, where Kenaley is a research associate, in a phosphotungstic acid solution, which makes soft tissues visible to Xray imaging. They scanned the specimen while rotating it through 180 degrees, then digitally “stacked” the resulting pictures—thousands in all—to create an image that can be viewed from multiple angles. The yellow and orange hues represent soft tissue areas; the bright yellow vertical bands behind the eye are bundle-like muscle fascicles that control opening and closing of the jaw.

The rendering allowed Kenaley to gather measurements of the jaw and muscle system—the lengths of bones and muscles and the exact points of attachment—the geometry that he needed to determine the speed and force with which the jaw can open and close. With these guidelines, he used the lab’s 3D printer to produced the outsized six-inch by six-inch skeletal model. Wires connected to a small motor allow Kenaley to robotically simulate the jaw’s actions.

Kenaley’s determination, thus far: The teeth do not penetrate the scales of prey (indeed, a human would barely notice being pricked by them). But the viperfish’s musculature does enable it to close its mouth rapidly—in less than 50 one thousandths of a second. Kenaley is currently testing the robotic jaw in a tank of water, mimicking the drag and other hydraulic forces at play in the deep sea to explore the possible advantages of a fast but weak design.