Teeth as a feeding mechanism in an oral cavity (mouth) are functionally and locationally linked with jaws. In fossils, teeth found in the oral cavity are usually linked with jaws, although mineralised structures with the same histology as teeth are known in fossils before jaws appeared. Denticles in the skin occur in both fossil and extant fish. Pharyngeal denticles also occur in both extant and fossil gnathostomes but in only a few fossil agnathans (thelodonts). Complex structures with dentine and enamel have been described in the earliest jawless vertebrates, conodonts. Such fossils have been used to suggest that teeth and jaws have evolved and developed independently. Our understanding of the developmental biology of mammalian tooth development has increased greatly in the last few years to a point where we now understand some of the basic genetic interactions controlling tooth initiation, morphogenesis and patterning. The aim of this review is to see what this developmental information can reveal about evolution of the dentition.