Sea Walkers

In a surprising turn of evolutionary ingenuity, some fish species have developed legs that do much more than help them scuttle across the ocean floor.

The northern sea robin, Prionotus carolinus, sports a pair of “legs” which are actually specialized extensions of the fish’s pectoral fins. These appendages act as highly sensitive sensory organs that allow them to detect buried prey, like mussels hiding in the seabed, for example.

Marine biologist Nicholas Bellono and his team began studying the fish after hearing about its unusual hunting skills. They discovered that the fish could easily uncover prey even when it was hidden in sand or presented in a capsule with just chemical cues.

“To our surprise, they were very, very good at it,” Bellono told the Harvard Gazette.

The team identified sensory papillae on the legs – bumps similar to the taste buds on a human tongue – making them highly attuned to both touch and chemical signals.

Still, the study took a strange twist when researchers accidentally received a shipment of striped sea robins, Prionotus evolans, a different species. While these fish could walk just fine, they failed to locate their next meal.

“I thought they were just some duds,” joked Bellono.

It turned out the striped sea robins simply lacked the same sensory capabilities.

While the findings underscored evolutionary specialization between closely related species, the researchers sought to understand the genetic roots of these “legs.”

They came across an ancient gene called “tbx3a,” which regulates the development of fins and limbs in a variety of animals.

“This is an excellent example of making new body parts by modifying old, shared tools,” co-author David Kingsley explained in an interview with New Scientist.

The authors noted that the quirky walking sea robin could be used as a model for understanding how new traits evolve by shedding light on how evolutionary processes work in humans, too – after all, our ability to walk upright only evolved about six million years ago.