Paedomorphic Origin of the Anurans: A New Approach to Prove It

Sergei V. Smirnov


Anurans are proposed to be paedomorphic descendants of labyrinthodonts. This hypothesis is based on the similarity displayed by larval/juvenile dissorophoids and adult anurans. Firstly, anurans lack those cranial features that appeared lately in the labyrinthodont’s ontogeny: skull ornamentation, postorbital, postfrontal, supratemporal, tabular, and postparietal ossifications. Secondly, they show pedicellate teeth which were ontogenetically transient in dissorophoids. However, this similarity is a necessary, but not sufficient, condition to assume the paedomorphic origin of the anurans. To prove it, one must show this similarity to have been attained via changes in the rate of somatic/sexual development at the labyrinthodont-anuran transition. Paedomorphosis results from the acceleration of sexual/retardation of somatic development leading to the incomplete realization of the morphogenetic program. Features lost via paedomorphosis may remain as latent capacities: continuation of postmaturational ontogeny or secondary acceleration of descendant ontogeny may result in their re-appearance. Consequently, if anurans have originated via paedomorphosis, the re-appearance of labyrinthodont-like features is likely in old frogs or frogs with accelerated cranial ontogeny. Indeed, such animals display: a) skull ornamentation, b) additional bones likely corresponding to the postparietal, supratemporal, etc., and c) non-pedicellate teeth. Accordingly, the re-appearance of these ancestral features must be considered as evidence supporting the hypothesis of paedomorphic origin of anurans.


skull; teeth; Anurans; Labyrinthodonts; origin; paedomorphosis

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