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EleFact Friday: Muscles and Extension

We’ve written several EleFacts about the elephant trunk, and this week we’ll be looking at another aspect of the trunk – how it extends. The trunk is multi-functional in that it has to be gentle and flexible enough to grab tiny blades of grass, but tough enough to knock down trees. So, how does one body part approach doing both things?

In a recent study on African elephants, subjects were asked to reach far-away objects by only extending their trunks horizontally. Elephants can extend their trunks 10 to 20% to reach objects that are distant, but it was noted that there’s a dorsal (upper side) “joint” that stretches 15% more than the corresponding ventral section (lower surface). 

The dorsal skin is folded and 15% more pliable than the wrinkled ventral skin. Elephants commonly use the ventral trunk surface to wrap around and carry food. The ventral wrinkles may increase friction in the same way that wrinkles in human and primate hands do. At the joint, the skin requires 13 times more energy to stretch than the muscle. Tests showed that the underside of the trunk is nearly 2 times stiffer than the upper side. This stiffness can restrict motion at the tip, where nostrils take up much of the space. 

It’s been shown that elephants have a near-perfect success rate in lifting various sized objects when using the distal tip of the trunk. They rarely use the dorsal part of the trunk for gripping. However, the dorsal trunk provides sun protection, cushioning when pushing tree trunks, and impact protection during fights, should that be necessary. What the study effectively shows is that it appears that the elephant trunk has different functions depending on the location of the muscles and the pliability of the skin. 

If you want to read more about the study details, you can find it here: 

https://www.pnas.org/doi/epdf/10.1073/pnas.2122563119

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