Ontogenetic aspects of dental evolution.

The evolution of dental ontogeny in the vertebrates is reviewed. Teeth probably originated as dermal structures, which secondarily spread to the mouth, where they became associated with bones. Tooth formation is a repetitive process, resulting in spatially separate units, and primitively it continued throughout life. Development of conical teeth commences at the tip and extends basally; folding of the basal lamina of the inner dental epithelium results in complex shapes, as in mammalian molars. Heterodonty, the divergent development of the teeth in a dentition, has evolved in a number of vertebrates, particularly mammals. Experimental analysis of dental development is still at an early stage, and the explanation of evolutionary changes in developmental terms is largely speculative Mammals are atypical vertebrates in many ways, and more studies of lower vertebrates, especially fishes, are needed.