The Provisional Dermal Folds in the Oral Apparatus of the American Paddlefish Polyodonspathula Walbaum, 1858 (Acipenseriformes, Polyodontidae).

The transitory dermal infoldings are described for the first time in front and behind the upper jaw in the larvae and postlarvae of the American paddlefish, Polyodon spathula Walbaum, 1858. In sturgeons these infoldings are necessary for the jaw protraction. In the paddlefishes, they, probably recapitulate the ancestral state. At the same time, the presence of these folds at the larval stages might indicate that the paddlefish larvae possess the protractive jaws. Further developmental studies of the jaw kinematics in Polyodon spathula are needed to test both hypotheses.