Stretchy, Telescoping Skin Is the Key to Elephant Trunks

New findings could help develop better robotics.

African elephant reaching out toward the camera
Madelein_Wolf / Getty Images

Watch an elephant reach for a tall branch or a drink of water, and its trunk unfolds and stretches little by little to meet its goal.

But the mammoth mammal doesn’t just use its muscles to make the move. A new study suggests that the folded skin covering the trunk is key to stretching.

Researchers at the Georgia Institute of Technology collaborated with Zoo Atlanta to study how the combination of skin and muscles works together to allow elephants to reach far for vegetation and has the force to tear tree trunks.

And what they learned may help in designing better robotics.

“The research started as a goal to design more advanced robotics for humans to use,” lead author Andrew Schulz, a Ph.D. student in mechanical engineering at Georgia Tech, tells Treehugger. “But through the project it has become more important to focus also on the sustainability impacts of the goal and how we can help benefit elephant conservation from understanding their biomechanics, a field known as conservation physiology.”

Elephant trunks are an interesting mix of muscles that work together. Those muscles work with the gathered, wrinkly skin that covers the appendage.

“An elephant's trunk has a collection of different muscles allowing them to stretch, shorten, twist, and bend!” Schulz says. “The skin plays an essential role in trunk elongation as the skin is directly connected to the exterior of the trunk’s muscle; therefore, as the muscle moves, the skin, which has deep wrinkles, helps the trunk stretch while maintaining its strength.”

Telescopic Trunk Umbrella

For their study, researchers filmed two African savanna elephants reaching for apples and cubes of bran at the zoo, then studied the video to watch how the trunk worked when stretching.

Instead of evenly extending out, they found that it moved telescopically like an umbrella. This was very different from squid and octopus tentacles, which are also boneless, muscular appendages.

“We were expecting to find that the elephant trunk stretches similar to the other muscular hydrostats (tongues and tentacles), but we found something completely different,” Schulz says.

“The elephants are stretching differently on the top and the bottom of their trunks due to the skin on the top and bottom portions containing asymmetries which are explained by the elephant skin.”

The top of the trunk is more flexible than the bottom part of the trunk. When the trunk reaches more than 10% extension, the dorsal part starts to extend further than the ventral section.

The elephant first extends the section of skin around the tip of its trunk, then the next section, and the next. The gradual movements from tip to body are intentional, according to researchers. Schulz says elephants are lazy, like people.

“Saying elephants are lazy like us is a biological necessity!” Schulz says. “Elephants don’t like wasting energy and therefore, when they stretch their trunks like a telescoping pole, they begin with the front tip as it contains only one liter of muscle. This volume compared to the base of the trunk (near the tusks) has nearly 11 liters of muscle, therefore the elephant is being energetically efficient in their stretching by moving the tip before the base.”

Schulz says he used a drawing from 1908 when he was researching elephant trunk anatomy because there hasn’t been much research on biomechanics of the animal during the past century or so.

The findings were published in the journal Proceedings of National Academy of Sciences (PNAS).

Robotics and Conservation

Study results shed more light on understanding elephant anatomy and biomechanics, but they might be able to help those designing soft robotics. They can also offer insight in the field of conservation.

“We look to gain inspiration from the elephants, but it is important to think about the conservation ties of these animals that are currently predicted to be extinct in the wild in the next 15-20 years,” Schulz says.

“In elephant anatomy we have been able to quantify elephant skin and its function in working with the muscle to elongate. In the conservation ties we see different anatomy interactions that would help with skin repair from elephants that are injured in the wild as assisting with skin punctures around the trunk.”

View Article Sources
  1. Schulz, Andrew K., et al. "Skin Wrinkles and Folds Enable Asymmetric Stretch in the Elephant Trunk." Proceedings of the National Academy of Sciences, vol. 119, no. 31, 2022, doi:10.1073/pnas.2122563119

  2. lead author Andrew Schulz, a Ph.D. student in mechanical engineering at Georgia Tech

  3. "Skin: An Additional Tool for the Versatile Elephant Trunk." Georgia Institute of Technology.