The elephant has a secret hidden on his nose.
Its famous trunk, muscled and boneless, can move in an almost infinite number of directions and is capable of a variety of tasks, such as shredding foliage and sucking up water and tortilla chips. These skills have inspired wildlife enthusiasts and engineers alike who are working to build robots capable of comparable feats of flexibility and strength.
But the trunk is more than just muscle, and its abilities may also depend on something obvious but often ignored: the skin of the appendage.
In a study published Monday in The Proceedings of the National Academy of Sciences, researchers report that because of important differences in skin pliability in different zones, an elephant’s trunk extends more at the top that faces outward than it does. at the bottom, closer to the mouth.
The trunk is “a muscular multi-tool that can do all these things, but one of the tools it carries in its back pocket is all this different skin,” said Andrew Schulz, a doctoral student in mechanical engineering at the Georgia Institute of Technology and an author of the new study.
As part of an ongoing collaboration with Zoo Atlanta, Mr. Schulz and his colleagues challenged two African elephants — a male and a female — to extend their trunks horizontally to grab food placed far away.
The simplicity of this reaching motion belies the complexity of what the torso is supposed to do.
When viewed on a high-speed camera, the elephant’s trunk doesn’t extend evenly like other muscle appendages, such as octopus arms or your tongue. Instead, the trunk slides outward, with the tip extending first, followed by the front half of the trunk.
The researchers hypothesize that this telescoping behavior may be more energy efficient than moving the entire trunk. If the torso were divided into quarters, there would be about a liter of muscle at the tip, but a whopping 22 liters of muscle at the base, which would be heavy and energy-intensive if the movement were more even.
And with even more detailed analysis, the researchers noticed that “weird asymmetries are popping up everywhere, as if things were different at the top and bottom,” Mr. Schulz said. As the elephant’s trunk lengthened, the outward-facing half extended 15 percent further than the ground-facing half.
“I remember literally running like an idiot to my consultant’s office with my laptop in my hand to show him some of these results because it’s so surprising,” said Mr. schulz.
Initially, the researchers thought this top to bottom difference in hull stretching was a flaw, but further mechanical testing dispelled those doubts.
When they stretched skin samples taken from a frozen trunk preserved from an elephant that died in a zoo, the researchers found that the skin on the top of the trunk, with its long folds, was 15 percent more pliable than the wrinkled ones. covered skin from the underside of the torso.
These different characteristics correspond to the different functions that the skin provides. The top surface of an elephant’s trunk needs to be protected from both the sun and other animals, and it has this “flexible armor like Kevlar with these deep folds that are very, very easily expandable,” Mr Schulz said. The underside of the hull, on the other hand, is covered in smaller wrinkles and is used for grasping and moving objects, but rarely sees the light of day.
The new study is a good reminder of “the involvement of the skin itself in biomechanics,” said Michel Milinkovitch, a professor at the University of Geneva who has researched the biomechanical complexity of elephant trunks.
For engineers who take inspiration from elephants, it’s essential to realize that not only should they focus on their robots’ motors and other internal materials, but also think about “playing with the geometry of the packaging,” said Dr. . Milinkovitch, who was not involved. in the study. “Nobody has really put this into real robots yet,” he added.
While the research opens up new possibilities for future robots that more accurately mimic the powers of the elephant’s trunk, it also underscores the importance of preserving the endangered species that know best how to handle these wondrous tools.
“Bioinspiration is great until none of the animals we get bioinspired from exist,” said Mr. Schulz.