Square tail mystery unravelled

Researchers have found that the square cross-section of seahorses’ tails allows better gripping and grasping than round-shaped tails.

Scientists at the University of California in San Diego have used 3D-printed prototypes of a seahorse skeleton and discovered the square shape allows a better gripping action than a circular-shaped tail. It was also stiffer, stronger and more resistant to strain making it more effective armour as it is.

“Almost all animal tails have circular or oval cross-sections – but not the seahorses’. We wondered why. We found that the squared-shaped tails are better when both grasping and armour are needed,” said research leader Dr Michael Porter.

In the study, published in Science, the team studied 3-D printed prototypes of square plates that surround the central backbone of seahorses and tested their characteristics by comparing them to round-shaped prototypes.

“New technologies, like 3D-printing, allow us to mimic biological designs, but also build hypothetical models of designs not found in nature. We can then test them against each other to find inspiration for new engineering applications and also explain why biological systems may have evolved,” said Dr Porter.

By twisting the prototypes they found that the square plates limited the range of movement by about half compared to the model made of round segments. After twisting, the square model returned to its original shape faster than round segments. A tail with square segments also has more contact points with the surface it is gripping.

The team also found a square tail makes far better armour than a circular one. The scientists were able to observe how square plates only slide when crushed as opposed to circular plates that slide and rotate. As a result, the square plates absorbed much more energy before permanent failure begins.

The findings could be applied to build a gripping robotic arm that can be used in hostile environments.