The supernumerary postcanine teeth were examined in the kuril seal (Phoca vitulina stejnegeri), the larga seal (P. largha) and the ribbon seal (P . fasciata). Supernumerary postcanine teeth were found in 6.56%, 6.03% and 11.76% of them respectively. On the other hand , 1.31% of the kuril seal, 0.86% of the larga seal and 11.76% of the ribbon seal were found to have missing teeth. So, in these three species, there is a greater percentage having supernumerary teeth than missing teeth. This is a

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... re situation in mammals because missing teeth are more common than supernumerary teeth in many species. As the position in which supernumerary postcanine teeth were found are commonly variable, it is thought that the cause of supernumerary postcanine teeth is due to a splitting of the tooth germ rather than atavism in the kuril seal and the larga seal. Also the positions of the supernumerary teeth in the kuril seal are different from the larga seal. This difference is presumed to stem from the differences in the foetal developmental process of the maxilla and mandible of the two species.