polyphyodont

Polyphyodont describes animals that continually replace teeth throughout life. In polyphyodont species, the dentition is renewed multiple times, in contrast to diphyodont species that have two successive sets (deciduous and permanent teeth) and monophyodont species that form only a single set.

Most sharks and many reptiles are polyphyodont. Sharks replace worn teeth from a conveyor belt–like sequence of developing teeth along the jaw, producing new replacements continuously. Crocodilians also replace teeth throughout life, though the rate is slower and replacement is more discrete. Some snakes and many lizards exhibit ongoing tooth replacement as well. Birds lack teeth altogether, and most mammals are diphyodont, possessing a deciduous set followed by a permanent set; a few mammalian lineages have limited or regionally restricted replacement.

The underlying mechanism involves the formation of new tooth buds from dental epithelium at the margins of the jaw, often driven by the dental lamina or related tissues. Replacement teeth typically develop behind the functional tooth and erupt as wear or loss creates space. The exact timing, rate, and pattern of replacement vary widely among polyphyodonts and are influenced by ecological and life-history factors.

Ecological and evolutionary significance includes maintaining functional dentition in the face of wear from abrasive diets and environmental conditions. Polyphyodont dentition can extend feeding ability and survival in species exposed to high tooth wear, contributing to their foraging strategies and ecological niches.

See also: diphyodont, monophyodont.