Diversity and development of labial tooth row formulae in tadpoles

Keratinized labial teeth of the oral apparatus are a conspicuous evolutionary novelty of anuran tadpoles. Although several comparative studies have investigated their diversity in shape, arrangement, and function, no attempts have been made so far to explore taxonomic distribution and relationship with ontogenetic patterns at a global level. In this paper, we survey the variation in labial tooth row numbers in tadpoles in a phylogenetic context and discuss the developmental patterns probably involved in interspecific disparity. A configuration of two upper and three lower tooth rows occurs in almost half of free-living tadpoles but mostly concentrates in Notogaeanura; in Indianura, three rows are frequent in the lower lip but combined usually with increased numbers in the upper lip. While the homology between individual rows in this 2/3 and lower configurations seems straightforward to assess, the diversity of addition pattern of tooth rows in the upper and lower lips of tadpoles belonging to different clades merits the development of alternative terminology and refined coding systems for future phylogenetic analyses.