How the elephant got its wrinkles Sara Reardon, Science October 8, 2024 An elephant’s trunk is so much more than a nose. The pachyderms use their prehensile probosces to pick up food, spray water or sand across their backs to cool off, and trumpet warnings to other elephants. Baby elephants even employ their trunks to nurse, sucking up milk and then spraying it into their mouths. “It’s the most unbelievable grasping organ on the planet,” says computational neuroscientist Michael Brecht of the Humboldt University of Berlin. But why does the trunk —a muscular appendage without any bones —work so well? One key is an elephant’s famed wrinkles, which—on the trunk—act like hands and elbows, Brecht and colleagues report today in Royal Society Open Science. The team also discovered where these wrinkles come from in the first place—and how they help make trunks so versatile. When Andrew Schulz, a mechanical engineer and biophysicist at the Max Planck Institute for Intelligent Systems, started to look at elephant trunks, he assumed their characteristic wrinkles developed over time as the animals used them repeatedly—much like smile lines that form in human faces. But he soon realized that even newborn elephants have wrinkly trunks. Many baby animals—including humans—are born with random wrinkles because they have too much skin for their body shapes. Baby elephants’ trunk creases, by contrast, are consistently in the same places and form before birth, suggesting they have a specific purpose. “We think these wrinkles are very underrated,” Brecht says. To learn more, Schulz, Brecht, and their colleagues turned to two elephant species, Asian elephants (Elephas maximus) and African elephants (Loxodonta africana), which are known to use their trunks in different ways. African elephants have two tough cartilage “fingers” at the ends of their trunks that allow them to pinch objects. Asian elephants, by contrast, have one finger and one bulbous projection that they use to clamp large objects such as melons between their trunks and lower lips. The researchers examined differences between the species in museum specimens, zoo animals, and photos. Asian elephant trunks, they found, contain more wrinkles: 126 of them, on average, compared with the 83 of African elephants. The extra creases might give the Asian species more flexibility to make up for not having an extra “finger,” Schulz says. In both species, the wrinkles were concentrated at a pivot point, which works like a muscular elbow to allow the trunk to wrap around objects. To study how these wrinkles form, the team gathered two Asian and three African elephant fetuses in museum collections, along with dozens of published photographs or drawings of fetuses at different ages. By lining these up sequentially, the researchers were able to form a visual timeline of prenatal trunk development. Wrinkles, they found, begin to appear as soon as the trunk does—about 20 days into the elephant’s 22-month gestation. Over the next 150 days, the number of wrinkles increases exponentially in both species, doubling every 3 weeks, and concentrates around the pivot point. Asian elephants acquire even more wrinkles later on in development. The scientists next looked at whether trunk use contributes to additional wrinkle formation, as they originally suspected. Elephants are either left- or right-trunked, meaning they consistently bend the appendage to one side to put food in that side of the mouth. Over time, the researchers found, this bending creates more wrinkles on one side than the other. It isn’t yet clear whether “trunkedness” is controlled by the brain, as it is in humans, or whether wrinkle patterns make it easier to use one side than the other, says John Hutchinson, an expert on animal locomotion at the Royal Veterinary College who wasn’t involved in the paper. Studying this, he says, would require researchers to follow the long-lived animals consistently for years. Not much is known about the genetic and molecular mechanisms that lead to trunk and wrinkle formation, because of elephants’ long gestation periods and ethical concerns about manipulating elephant embryos. But that might be a question for future research, Brecht says. “I’d like to know how he makes his giant nose.” The paper is solid and interesting, Hutchinson says. He is curious about wrinkle formation in ancient species such as woolly mammoths, which seem anatomically closer to Asian than African elephants and only have one finger on the ends of their trunks. Schulz hopes the research will inform work on soft robots used in disaster response. These robots’ joints are controlled by moving hydrostatic pressure around, much like elephant trunks, and their flexible bodies allow them to sneak into small spaces. Elephants are the ideal model for studying soft joints, Hutchinson says. Although other animals such as primates and elephant seals can inflate organs by pumping blood into them, none of them have the specialized joints and dexterity of elephant trunks. “Elephants are doing their own thing,” he says. “Elephants are singular.” https://www.science.org/content/article/how-elephant-got-its-wrinkles