Public Release: 

Be square, seahorse; it has mechanical advantages

American Association for the Advancement of Science

This news release is available in Japanese.

The seahorse tail is square because this shape is better at resisting damage and at grasping than a circular tail would be, a new engineering study shows. Insights gleaned from the study could inspire new armor and advances in robotics, the authors say. While most animals with tails, including certain monkeys, lizards and rodents, have soft, cylindrical-shaped appendages, tails of seahorses are organized into square prisms surrounded by bony plates. To better understand why the seahorse tail deviates from the norm, and what mechanical advantages its curious tail shape might confer, Michael Porter and colleagues created a 3D-printed model of the tail, as well as a hypothetical cylindrical version. The researchers twisted and bent both models, and hit them with mallets, finding that the square version was more resistant to twisting, better able to return to its natural alignment. The twisting resistance of the square tail may help protect the seahorse's delicate spinal cord. The outer surfaces of the square tail also increase contact area when the tail wraps around an object, the researchers found, giving it better grasping control. Finally, the square version was also more resilient, not deforming as drastically as its round counterpart. This resilience was facilitated by gliding joints, as illustrated in a related computer animation. Scientists have been taking inspiration from nature to design new technologies, like search-and-rescue robots, for years, and this new study will add to their ability to do that, particularly as the seahorse tail, though hard, is compliant (a quality difficult to achieve in metal robots) and though light in weight is damage-resistant (a quality challenging to realize in silicone-based bots). The study also shows how engineering designs can answer biological questions. A Perspective provides additional insights.

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Article #8: "Why the seahorse tail is square," by M.M. Porter at Clemson University in Clemson, SC; D. Adriaens at Ghent University in Ghent, Belgium; R.L. Hatton at Oregon State University in Corvallis, OR; M.A. Meyers; J. McKittrick at University of California, San Diego in La Jolla, CA.

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