The development of the tooth pattern and dentigerous bones in Polypterus senegalus (Cladistia, Actinopterygii)

The formation sequence of the tooth-bearing bones and the tooth pattern in early ontogeny of Polypterus senegalus is investigated using transparent pr eparation, histological sections, and SEM. During the attachment step of th e yolk-sac larva the first dermal bones and teeth are formed. Teeth appear simultaneously in the areas of the maxillary, dentary, dermopalatine, pre a rticular, and coronoid 1 along with the first separate anlagen of these bon es. A monostichous arrangement of primary teeth is established on the maxil lary, dentary, and dermopalatine. Polystichous tooth arrangements do not oc cur before the early pterolarval phase, and then only in connection with bo nes of the palate and inner dental arcades. Especially pronounced is the in fluence of tooth formation on the structure of the parasphenoid that become s much thickened by accretion of denticulate platelets, but we found neithe r evidence for a distinct vomeral contribution to the parasphenoid. nor a c omposite origin of the ectopterygoid in ontogeny. First replacement teeth a re found in association with the maxillary and dentary as early as the late apterolarval phase. Primary teeth are of a single general type, whereas fr om the pterolarval phase onward three tooth types can be distinguished that are restricted to certain tooth bearing bones. Relatively late in ontogeny , dermo-metapterygoid and entopterygoid become formed and colonised by teet h, whereas first branchial teeth and tooth plates appear earlier during the first phase of extrinsic larval feeding. Characteristics of development of the dentition are discussed in comparison with character states of other b etter known fossil and recent taxa among Actinopterygii and Sarcopterygii. Compared to the assumed basic pattern of actinopterygian fishes, Polypterif ormes show a derived condition with respect to structure, arrangement, repl acement, and differentiation of teeth, which arises in sequence during larv al development. This also corresponds to observed changes of feeding behavi our and functional demands during larval life.