Development of the teeth in a pouch-young specimen of Isoodon obesulus and one of Perameles gunnii (Peramelidae: Marsupialia)

Abstract

The heads of one pouch-young specimen of Isoodon obesulus, snout-occiput length 3 cm, and one pouch-young specimen of Perameles gunnii, snout-occiput length 3.5 cm, were sectioned transversely and the tooth germs and dental laminae were graphically reconstructed. In Isoodon obesulus, the replacing premolar developed terminally on a dental lamina lingual to the deciduous premolar in both jaws. In the upper jaw this lamina was isolated, while in the lower jaw it remained connected to P 2 for a short distance. In Perameles gunnii, there was no trace of the replacing premolars although a marginal thickening of the dental lamina lingual to dp could be followed for about 500 μm in both jaws. These laminae were nowhere connected to P 2 2 or dp. Since the earliest differentiation of the replacing premolars on the isolated dental laminae must start in a definite lingual position to dp in Perameles gunnii, difficult to accept that the replacing and deciduous premolars are in series. In Isoodon obesulus, the enamel of the deciduous premolar was well developed in both jaws, whereas in Perameles gunnii this tooth had a very thin enamel layer and irregular dentinal tubules, its structure resembling that of the mandibular abortive tooth germ. In both specimens, the germ of M 3 was in the cap stage and was endostichally connected to an isolated dental lamina. The germ of M 4 was in the cap stage in Perameles gunnii and was terminally situated on the dental lamina which had no connection with M 3. In Isoodon obesulus, the germ of M 4 was not found, but was supposed to start its differentiation somewhere on the horizontal lamina which was parietally connected with M 3. It is demonstrated that several differences exist between Isoodon obesulus and Perameles gunnii as to the degenerative rate of the dental laminae and the development of the teeth.