Researchers from the University of Antwerp in Belgium have identified an unusual fish that forms a tongue-like structure out of water so that it can feed on land, and the discovery could shed new light on how vertebrates originally emerged out of the water.
Lead author and biomechanist Krijn Michel and his colleagues, who reported their findings in the March 18 online edition of the Proceedings of the Royal Society B, reported on the unusual feeding behaviors of the mudskipper (Periophthalmus barbarus), which uses water held in its mouth like a hydrodynamic tongue in order to capture and manipulate prey.
According to Discovery News, the point at which a handful of fish left the water and took to the land some 350 to 400 million years ago was “one of the most pivotal moments” in evolution, as those creatures developed into the first tetrapods (four-legged land animals) and ultimately went on to become amphibians, reptiles, birds, and mammals.
To determine how this transition took place, scientists typically research how the limbs of those early tetrapods evolved over time, the website said. However, Michel and his co-authors took a different approach: studying how these first land animals developed the ability to eat on land.
“To capture and swallow food on land, a sticky tongue… has evolved in land vertebrates from aquatic ancestors that used mouth-cavity-expanding actions of the hyoid to suck food into the mouth,” the study authors wrote. “However, the evolutionary pathway bridging this drastic shift in feeding mechanism and associated hyoid motions remains unknown.”
“Modern fish that feed on land may help to unravel the physical constraints and biomechanical solutions that led to terrestrialization of fish-feeding systems,” they added. “Here, we show that the mudskipper emerges onto land with its mouth cavity filled with water, which it uses as a protruding and retracting ‘hydrodynamic tongue’ during the initial capture and subsequent intra-oral transport of food.”
We bet they are really good at French kissing
Fish generate suction with their mouths when in the water, drawing in food with the help of a neck bone called the hyoid. On land, however, it proved impractical to suck in air to swallow food. In response, tetrapods evolved tongues supported by the hyoid that helps food make it down the throat, but little is known about exactly how these tongues developed.
Michel’s team conducted experiments using five Nigerian mudskippers, hoping to learn more about the process through which tongues evolved. Using high-speed video cameras and X-ray scanners, they captured footage of the fish eating and showed how they used the water in their mouths like a tongue to reach out, capture the prey, and then quickly swallow it.
“First it spews out the water, then very rapidly… it’s sucking the water back up again. They’re using the water that is in their mouth as a substitute for a tongue,” Michel told Nature. “They’re very good at feeding on land. We put the food there and within a fraction of a second it’s gone. They’re remarkably bad at feeding underwater. They miss the food completely sometimes.”
“Our analyses link this hydrodynamic action of the intra-oral water to a sequence of compressive and expansive cranial motions that diverge from the general pattern known for suction feeding in fishes,” he and his co-authors wrote. The hyoid motion had “a remarkable resemblance” to that of newts “during tongue prehension” and that “hydrodynamic tongue usage may be a transitional step” in the evolutionary processes required for terrestrial foraging, they added.