Monophyodonty

Monophyodonty is a dental condition in which an individual develops only a single set of teeth and does not replace teeth after eruption. The term comes from Greek monos, meaning single, and odous, meaning tooth. It is used to contrast with diphyodonty, in which two successive dentitions occur (deciduous and permanent), and polyphyodonty, in which teeth are replaced repeatedly over a lifetime.

In practical terms, monophyodonty means that once teeth are erupted, there is no ongoing replacement to compensate for wear or loss. This pattern is observed in some evolutionary lineages where tooth replacement offers little selective advantage, or where developmental trajectories favor a single dental generation. The most well-known examples are among the monotremes, such as the platypus and echidnas, whose adults lack true teeth; they rely on alternative structures for food processing, while earlier developmental stages may form temporary dental structures. In other groups, true monophyodonty is rarer, and many species show at least some tendency toward tooth replacement, even if infrequent.

Evolutionary interpretations of monophyodonty emphasize ecological and developmental factors. A single dentition can be advantageous in environments with stable diets or where the costs of continual tooth replacement outweigh the benefits. Conversely, tooth loss or reduced replacement can impose constraints on feeding, wear resistance, and lifespan. Comparative studies of dentition patterns contribute to understanding how development and ecology shape dental evolution across vertebrates.

See also: dentition, tooth eruption, homodont, heterodont.