For an elephant trunk, it’s all in the bone joints

Researchers find that an elephant’s trunk forms a kind of joint to pick up small pieces of food, a technique they say could be used as inspiration for robotic arms. 

A team of researchers led by Jianing Wu at the Georgia Institute of Technology, Georgia, USA, videoed an African elephant (Loxodonta africana) eating small pieces of food and measured the force its trunk exerted throughout the exercise. They found that the animal swept the food into piles and then formed a joint to pick up as much as possible at once. 

“Forming joints may help reduce the energy required to reach for and grab food items, a task they perform for 18 hours every day,” the researchers write in the Journal of the Royal Society Interface. “The joint formation may also have application in elephant-inspired robots.”

To explore how the trunk works, the scientists offered an elephant small particles of food – wheat bran, chopped swedes, or chopped carrots. Elephants do not usually eat food reduced to such small pieces, but offering it in this form provided an effective way to see how the trunk could work. 

Wu  and colleagues found that elephants form a sort of joint at the trunk so it could clamp several bits together. {%recommended 5781%}

“Although the elephant trunk lacks bones, the formation of a joint mimics a common vertebrate strategy to reach out and grab objects,” the researchers note. 

Joints allow structures such as human limbs degrees of freedom, allowing them to reach a greater range of points in space. They also can provide leverage.

“This is why appendages without bones, such as the elephant trunk and octopus arm, have both demonstrated the formation of joints,” the researchers write. 

“The octopus forms a joint like the elbow only when retrieving food. Our study shows that the use of joints might be more common than once thought.”

This discovery could be of particular value to robotics designers. 

“Long flexible robots have long been of interest to the robotics community,” the study’s authors write. 

“Such researchers have turned to snakes, octopus and elephants for inspiration. However, even among these animals, the elephant stands out because the trunk can apply the greatest forces.” 

Indeed, the elephant’s trunk is the largest hydrostat – a type of boneless muscular organ – on land, weighing 150 kilograms. That weight accounts for some of the force it can exert. 

“Wild elephants may still apply the strategies we observed if they need to press downward with their trunk while feeding,” the authors conclude. 

“To remove the bark from a tree, vertical forces are required, and its possible the elephant may form joints for this task. Now that we have observed the formation of joints, future work will determine how often elephants use this strategy.”