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

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.

Structure of the caecilian Siphonops annulatus (Amphibia, Gymnophiona): general aspects of the body, disposition of the organs and the structure of the mouth, oesophagus and stomach

“…The presence of a single line of teeth in the lower jaw and a double one in the upper jaw, also described in other species, is probably related to the feeding habit. The irregular disposition and size of the teeth and our histological observations regarding the occurrence of teeth in different stages of development in adult animals suggest a continuous process of tooth replacement, as observed in other species of Gymnophiona by other authors (Lawson 1965;Wake 1976Wake , 1980. The histology of the initial part of the digestive tract of S. annulatus presents a series of structures and characteristics such as: (1) presence in the mouth of a stratified squamous epithelium associated with goblet mucous cells;…”

The pattern of tooth plate formation in the Australian lungfish, Neoceratodus forsteri Krefft

“…Replacement of teeth has been studied in some teleosts but the evidence cited does not support the "Zahnreihe" hypothesis (Norris & Prescott, 1959;Ciardelli, 1967). Replacement patterns in Hypogeophis rostratus (Gymnophiona) and in Plethodon cinereus (Caudata) are consistent with Edmund's hypothesis (Lawson, 1965;Lawson et al, 1971) and this is also true in Hana pipiens (Gillette, 1955) but not in other species of Anura (Goin & Hester, 1961;Lawson, 1966) nor in Necturus maculostis (Caudata), where replacement patterns are very irregular (Miller & Rowe,197 3).…”

Evolution of vertebrate viviparity and specializations for fetal nutrition: A quantitative and qualitative analysis

“…From its phylogenetic distribution, this “dermatophagic” pattern was suggested to be broadly ancestral, with the embryonic teeth by which it is accomplished having been modified in viviparous forms for oviductal feeding (Kupfer et al, ; Gower et al, ; Wilkinson et al, ). However, embryonic dentition in caecilians shows much diversity in structure and development (e.g., see Lawson, ; Wake, , 1993; Wake and Wurst, ; Greven, ). Thus, its homology throughout caecilians cannot be assumed.…”