A central aim of evolutionary developmental research is to decipher the relative roles of ecological and molecular interactions in explaining biological diversity. Tetrapod teeth show diverse evolutionary patterns with a repeated increase in dental complexity, especially in response to herbivorous habits. Most extensively in mammals, dentition increases in complexity by elaborating morphology of individual teeth rather than increasing the number of teeth. Even though evolution of mammalian dentition is governed by ecology, recent evidence on molecular signalling suggests that many details and even some general evolutionary tendencies may be instigated by development. Specifically, iterative use of the same developmental modules, the enamel knots, may have facilitated developmentally efficient, or economical, elaboration of tooth shapes without substantially compromising the existing morphology. These kinds of developmentally influenced tendencies may be hypothesized to be typical to many organs and systems showing repeated evolutionary patterns.