Heterochrony in the development of vestigial and functional deciduous incisors in rabbits (Oryctolagus cuniculus L.)

Foetal and postnatal development of vestigial and functional deciduous incisors was reexamined using routine serial histological sections of maxillae and mandibles at daily intervals from day 16 postconception to postnatal day 15. It was found that the development of the maxillary and mandibular vestigial incisor teeth was more rapid than that of the functional incisors and that, of the functional incisors, the maxillary posterior deciduous incisors were the slowest to develop. It appeared from this study that a basic morphogenetic requirement for unfolding structure, ie, developmental timing, was not critical in generating hypsodont or brachydont teeth. A proposition has been made that originally juvenile stages of odontogenesis represent a continuously growing system, which during evolution has successively become typical for adult descendants.