Cownose ray uses its tail as a fine-tuned antenna, new study finds

A pair of marine biologists at Harvard University has found that one of the main purposes of the cownose ray's tail is to serve as a fine-tuned antenna. In their study published in the Proceedings of the Royal Society B: Biological Sciences, Júlia Chaumel and George Lauder dissected multiple cownose ray specimens to learn more about their tail anatomy.

Stingrays inject venom from their barbed tails into hapless victims. But other rays, such as mantas, do not have similar barbs on their tails, which has raised questions about their purpose.

The tails of manta rays and their close smaller relative, cownose rays, are long and thin, quite often as long as the rest of their body. Manta rays and their kind are also different in that they live in the open ocean, rather than in shallow water near shorelines—they also migrate long distances. For this new study, the researchers took a closer look at the cownose tail, hoping to determine its purpose.

Noting that the tail is too thin to propel the ray through the water or even to control its direction, the researchers looked at video of them in action. They found that the rays did not seem to use their tails when under attack by predators or when feeding on oysters, clams and other invertebrates. They next turned to pickled specimens collected and stored at the Harvard Museum of Comparative Zoology, and a pair of dead specimens that had recently been found by locals.

After dissecting the tails and putting them in a CT scanner, they found that the tail was covered with tiny holes, which were in turn connected to a lateral line canal—a line of sensory organs found in amphibians and many types of fish. The lateral line, they found, ran the length of the ray's body and was also connected to the ray's skin.

The finding strongly suggests the tail is a sensory organ. The researchers suggest that it serves as an antenna of sorts, allowing the ray to feel water movement, such as that made by a shark following behind. This would be important for a creature that cannot see behind it when digging in the mud at the bottom of the sea for food.

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