Via New Scientist:
It's relatively well understood how the first fish began to move on land and breathe in air, but how vertebrates switched from feeding via suction to evolve a tongue remains unclear. Seeking an answer, Krijn Michel at the University of Antwerp in Belgium and his colleagues looked to the mudskipper.
They captured high-speed X-ray footage of Atlantic mudskippers (Periophthalmus barbarus) out of water pouncing and chowing down on pieces of brown shrimp. The move takes less than half a second but, slowed down 50 times, they spotted that mudskippers carry water in their mouths, which they spit forwards to help grab food then suck it back to swallow, mimicking the action of a tongue.