The development and replacement of teeth in Hypogeophis rostratus (Amphibia, Apoda)

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Abstract

The details of tooth development in Hypogeophis rostratus are described and analysed by dividing the life cycle of the tooth into a number of stages. Such divisions are based on either morphological characters or the degree of change which occurs during equal fractions of the whole life cycle. On the basis of such data it is apparent that some phases of the development of the tooth take place slowly whilst others are passed through more rapidly. Such variations result in the production of a dentition in which each locus is generally occupied by a functional tooth and a replacement tooth at an earlier stage of development.

The process of tooth development in general follows the pattern described in Salamandra maculosa by Kerr (1960), and the enamel which covers the major and minor cusps of the adult tooth is considered to be of ectodermal origin. A stage at which the enamel matrix occurs in an uncalcified stage has not been found in Hypogeophis rostratus and it is assumed that calcification of the enamel occurs almost simultaneously with the production of its organic matrix. The crown and the pedicel of the mature tooth are connected by a ring of fibres, and it seems likely that the asymmetrical pedicel is ankylosed to the jaw bone by a thin layer of cement.

The mechanism of tooth succession is investigated and it is clear that both tooth production and tooth replacement occur in a synchronous manner. The term Zahnreihen (Woerdeman, 1919, 1921, and Edmund 1960, 1962) is accepted, and used in the description of tooth succession. It is clear that tooth production and replacement occur in much the same manner as in the reptiles (and possibly in all non-mammalian vertebrates (Edmund, 1960)) and can be explained by the fact that the Zahnreihen are on average 2·4 tooth spaces apart and that each replacement wave (which travels craniad along the jaw) usually contains about six teeth. The results obtained in H. rostratus in no way conflict with the idea that the Zahnreihen are produced by stimuli which travel caudad along the jaw and that the replacement waves may run in the reverse direction.

A theoretical template based on Zahnreihen 2·4 spaces apart is constructed and shows that replacement waves contain six teeth and run craniad along the jaw. It is pointed out that the observed facts do not exactly follow the theoretical pattern in that the distance between successive Zahnreihen may vary and that replacement rows may involve more or less than six teeth. Finally it is affirmed that such deviations are to be regarded as normal variations in the process of tooth production and replacement.

Ancillary