Which shark is recognized as the only known omnivorous shark species?

The bonnethead shark is recognized as the only known omnivorous shark species.

Bonnetheads are small hammerhead sharks found in shallow coastal waters of the western Atlantic and eastern Pacific. Their diet includes crustaceans, small fish, and seagrass. Unlike most sharks, which are treated primarily as carnivores, bonnetheads digest and obtain nutrients from plant material as well as animal prey.

A 2018 study provided strong evidence that bonnetheads actively digest seagrass rather than merely swallowing it incidentally. Researchers found digestive enzymes and nutrient absorption associated with the plant diet, showing that the shark can use seagrass as a meaningful food source. This makes the species an important example of unusual feeding adaptation among sharks.

The bonnethead is a member of the hammerhead family, Sphyrnidae, but it has a much smaller, smoothly rounded head than larger hammerheads. The tiger shark is sometimes called an opportunistic or broad-spectrum feeder because it eats many kinds of animals and objects, but that does not make it an omnivore in the same specialized sense.