Morphology and postnatal ontogeny of the dentition of Chthonerpeton indistinctum (Gymnophiona: Typhlonectidae)

The gross morphology, histology and postnatal ontogeny of the dentition of the viviparous and direct-developing typhlonectid Chthonerpeton indistinctum were described and compared with other caecilian species. C. indistinctum exhibited the typical pedicellated condition present in lissamphibians, with a conical monocuspid crown. Our histological analysis demonstrated that the tissue joining crown and pedicel was formed by two bands (internal and external), whereas the external band circumvented the complete periphery of the tooth junction. Likely this condition was not described for another gymnophionan species. In viviparous and some oviparous caecilians, dentition changes radically during ontogeny. Thus, there is a foetal dentition arranged in multiple rows of teeth (i.e. tooth patch), which is replaced by single tooth rows in neonate or juvenile individuals. Details of dentition in the lower jaw of neonate specimens are firstly reported for C. indistinctum herein, adding another member of Typhlonectidae. In some slightly larger specimens the foetal tooth patch on the lower jaw coexisted with a lingual row of the adult-type teeth, indicating that replacement of foetal dentition in the lower jaw did not take place just after birth. The number of teeth, a character widely employed among caecilian species descriptions, varies during postnatal ontogeny. Hence, we concluded that at least for typhlonectid caecilians, tooth number should not be considered as a character with a strong taxonomic value without considering the intraspecific ontogenetic variation. An extensive survey exploring the relationship between body length and tooth count becomes necessary to test the usefulness of tooth counts in species diagnosis.