Researchers studying the seahorse’s tail have found that square-shaped tails are better when both grasping and armor are needed. The finding could lead to building better robots, defense systems and medical devices.

Seahorse tails are organized into square prisms surrounded by bony plates that are connected by joints. Many other creatures, ranging from monkeys to rodents, have cylindrical tails.

An international team of scientists led by Dr Michael Porter of Clemson University wanted to know whether the square-prism shape gives seahorse tails a functional advantage.

“Almost all animal tails have circular or oval cross-sections – but not the seahorse’s. We wondered why,” said Dr Porter, whose research was published in the journal Science.

“Also remarkable, the square plates make the seahorse’s tail stiffer, stronger and more resistant to strain at the same time. Usually, strengthening any one of these characteristics will weaken at least one of the others.”

To find out, Dr Porter and co-authors created a 3D-printed model that mimicked the square prism of a seahorse tail and a hypothetical version that was cylindrical. They then whacked the models with a rubber mallet and twisted and bent them.

“New technologies, like 3D-printing, allow us to mimic biological designs, but also build hypothetical models of designs not found in nature,” Dr Porter said.

“We can then test them against each other to find inspiration for new engineering applications and also explain why biological systems may have evolved.”

The scientists found that the square prototype was stiffer, stronger and more resilient than the circular one when crushed.

The square prototype was about half as able to twist, a restriction that could prevent damage to the seahorse and give it better control when it grabs things.

Both prototypes could bend about 90 degrees, although the cylindrical version was slightly less restricted.

“The seahorse tail could inspire new forms of armor. It could also lead to search-and-rescue robots that move on the ground like a snake and are able to contract to fit into tight spaces,” Dr Porter said.

“We haven’t gotten that far with the applications side of things yet, but we see a lot of potential with this device because it’s so unique.”

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Michael M. Porter et al. 2015. Why the seahorse tail is square. Science, vol. 349, no. 6243; doi: 10.1126/science.aaa6683