DENTITION AND DENTIGEROUS BONES IN JUVENILES AND ADULTS OF POLYPTERUS-SENEGALUS (CLADISTIA, ACTINOPTERYGII)

Tooth types, their arrangement and the mode of tooth replacement were studied in juvenile and adult specimens of Polypterus senegalus by mea ns of scanning electron microscopy of cleared and stained specimens as well as sections. All the dermal bones of the oropharynx are almost c ompletely covered with teeth except for the angulare. The same is true for the branchial apparatus where only the hyoid skeleton is toothles s. The teeth are uniformly monocuspid and conical, but can be classifi ed according to shape and size into three types. These types and the m ode of tooth replacement are characteristic for each dermal bone. In s ome of the jaw bones each tooth possesses a lingually situated replace ment tooth. This is true for the teeth of the premaxillary, the maxill ary, and the dentary which are arranged in a single line, and those of the dermopalatine, the coronoids, and the vomer which are in several lines and graded in size. Replacement teeth of all the other dentigero us elements develop on top of existing pulpal openings, forming an ana stomosing common pulpal complex only after resorption of the previous tooth. The tooth plates of the dermal bones of the branchial apparatus are connected by syndesmosis only to the perichondrally ossified and to the cartilaginous or connective tissue material of the elements of the gill-arches. The dentition and its association with the bones of t he head in Polypterus senegalus bear resemblances to advanced actinopt erygians on the one hand (e.g. differentiation of tooth-types, arrange ment), but also some similarities to living Amphibia (anchoring materi al and mode of replacement) on the other. The accentuation of a single marginal line of large teeth in both, the outer and the inner dental arcade of the jaws is a peculiarity of Polypterus that in a way parall els the derived state of similar mono-linear tooth arrangements in Act inopterygii and Tetrapoda.