How a seahorse is akin to a theoretical robotic monkey

Seahorses are deviants, let’s just get that out of the way. They’re named after terrestrial quadrupeds for their face, the males defy convention by handling gestation, and now we’ve learned that they don’t agree with just about every other fish that tails are to be used for propulsion. If that weren’t enough, they’ve evolved the world’s first square tail, making them a better match for possible robots than other tail-reliant animals.

These tails aren’t just to look unusual, of course. While they’ve consolidated their locomotion to their fins, these tails are still employed regularly as anchors. Like a monkey or chameleon, they use their tails to wrap around objects like sticks or sea grass. Remaining stationary is a key component to their hunting, which relies on holding still in order to ambush small bits of shrimp and fish floating by in the water. To help master this important grip, their tail seems to have evolved a number of useful specializations.

The tail that makes for a better sea monkey

Replicas of the tail shape were created and found to offer a superior grip than most round, prehensile tails. The squared-off shape allows more surface area to come in contact with the anchoring object, making it more effective. While this tails shape sacrifices some flexibility, a tight grip is obviously more important than fluid movement when you’re trying to hang onto swaying kelp.

For the square shape to be rigid while retaining some flexibility, it had to be segmented, like a series of nested, square beads strung along the animal’s spine. Each segment was found to be very strong and resilient, retaining its shape after being subjected to pressures that would have deformed cylindrical tails. While large enough jaws can obviously overpower this armor, it would be enough to help protect the seahorse from smaller predators.

While humans aren’t looking to stalk shrimp more effectively, the grip and strength of the seahorses tail is of interest to robotics designers. On a large scale, just grips could be of use in dangerous rescue operations. On a small scale, this kind of small but considerable grip may be of use for internal medicine, where small pieces of tissue need to be held in place for surgery. There don’t seem to be plans, however, to replicate the weirdness of the seahorses themselves though.

Source: Why Seahorses Have Square Tails by Rachel Nuwer, Smithsonian