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The open, fanged mouth of a snake poised to strike is terrifying to most people. But William Ryerson is not like most people. Over the past few years, this herpetologist at the Cornell University College of Veterinary Medicine has peered into those mouths, analyzing the teeth’s shape, position, and size, and filmed them in action. This week at the annual meeting of the Society for Integrative and Comparative Biology, he reported that these factors can be used to predict the speed and direction of a snake’s strike.
“It’s cool to see this link between form and function,” says Lisa Whitenack, a paleobiologist at Allegheny College who studies fossil shark teeth. Elska Kaczmarek, a biomechanist at Northern Arizona University, notes that by combining anatomical observations with behavioral results, Ryerson can see “how the system works differently in snakes with different feeding strategies.”
Although herpetologists comparing snake species have long cataloged differences in their fangs—which are teeth modified to inject venom—they had largely ignored the rest of the teeth. “We had just assumed the teeth were all the same,” says Brian Richard, a comparative biomechanist at the University of Massachusetts Lowell who was not involved with the work.
But Ryerson found plenty of dental diversity when he peered into the open mouths of preserved specimens. Some snakes, such as boa constrictors, had long, slender upright teeth, whereas others, such as king snakes, had shorter, stouter, and more curved ones.
To get a more detailed view of the differences, Ryerson performed 3D x-ray scans and structural analyses of the upper and lower jaws and teeth of almost 70 snakes in 13 species, representing four of the five main groups of these reptiles. Using high-speed video, he also filmed each species as it attacked a dead rodent that had been warmed to body temperature, collecting footage of at least five strikes per snake.
Reviewing the snakes’ anatomy and attack videos, he found the teeth and strike behaviors roughly sorted into two categories, he reported Wednesday at the meeting. The clean division itself was surprising: “You often expect your experiments to be messier,” Ryerson says.
Boa constrictors and pythons are “strikers,” he notes. Their attacks are lightning-fast—covering some 2.7 meters per second—and tend to come from above their prey. Teeth in their lower jaw impale the prey first and help anchor the snake as it twists to reach up, over, and around the rodent in preparation for squeezing the life out of it. Then it clamps down with the upper jaw and thus secures its hold, he said.
In contrast, king snakes are “lungers,” attacking prey straight on, much more slowly—at about 1.5 meters per second—and piercing it with both the top and bottom teeth at the same time. Their gape is smaller than that of strikers. Both groups target rodents, though some species also eat birds, snakes, and other prey.
Strikers had greater dental variation, with tall, slender, straight teeth at the front of the lower jaw, and progressively shorter, broader teeth toward the back that curved toward the throat. Lungers’ teeth were broad and curved along the whole lengths of both jaws. The curvature enables the prey to easily slide deep into the mouth, but snags it if it tries to escape back out, Ryerson explained.
It makes sense that front teeth would be specialized for different types of attack behavior, says Savanna Wright, an undergraduate student at the University of California, Santa Cruz who discussed moray eel teeth at the meeting. “The [front] teeth are making the first contact.”
“I loved [the work],” Richard says. “We tend to oversimplify and say it’s just a strike, but where the snake hits, [its] tooth shape affect the force and velocity—and thus the snake’s chances of success at nabbing different types of prey.”
Ryerson hopes a better understanding of snake strikes will also inspire practical engineering applications. “If you need an object to pierce or grip something, it needs to be more than just sharp,” he explains. Like a snake’s mouth adapted to snatch different prey, “the shape of the tool could be informed by how the person might use it.”
