Often overlooked, this may be the most recent group to evolve flapping-wing flight. You’ve probably heard of the so-called "flying fish", which glides over the ocean, dipping its tail in the water for propulsion. Because it relies on the water for propulsion, the flying fish isn't really capable of powered flight.

There is another fish, called the freshwater hatchetfish, which may have a more developed flight adaptation. The nine species of hatchetfish inhabit the rivers of tropical South America. They often leap out of the water to catch their flying insect prey. Some books say the hatchetfish can rapidly beat its pectoral fins to propel itself through the air. The body of the fish has a deep, keeled shape, which is said to contain powerful muscles that attach to the front fins. Other sources say the hatchetfish only skims along the surface of the water, using its caudal (tail) fin, or that it merely jumps from the water like any other fish.

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