Paddlefish and sturgeon eggs are sold as caviar. American sturgeon and paddlefish populations were targeted as likely substitutes. There are also many species of tree frogs, and fish such as sturgeon and paddlefish. Their team successfully removed fossil field jackets which contained articulated sturgeons, paddlefish and bowfins. Fish include sharks, rays (such as the durophage "Myledaphus"), paddlefish, bowfins, gars, and teleosts. Selected species, like the paddlefish and alligator snapping turtle, would benefit from reduced harvesting. They also have fewer, thicker gill rakers than American paddlefish. Young American paddlefish are poor swimmers which makes them susceptible to predation. Paddlefish (family Polyodontidae) are basal Chondrostean ray-finned fish. Research suggests that the American paddlefish uses electroreceptors located on the rostrum to detect prey. There are 13 states that allow commercial or sport fishing for American paddlefish. American paddlefish are smooth-skinned and almost entirely cartilaginous. The largest American paddlefish on record was caught in 1916 in Okoboji Lake, Iowa. They are the only living species in the paddlefish family, Polyodontidae. The Missouri River also contains the pre-historic paddlefish.