The external gills and ornamentation of skull roof bones of the Lower Permian tetrapodDiscosauriscus (Kuhn 1933) with remarks to its ontogeny

Until now, the largest specimens of Discosauriscus (and also Utegenia and Ariekanerpeton - the Lower Permian members of the family Discosauriscidae) have been considered to be adult individuals. The largest specimens of Discosauriscus, in which the external gills are still present, had skull lengths of about 22-25 mm. Metamorphosis was believed to have commenced at this size in discosauriscids and specimens with skull lengths of about 50-54 mm were considered to be already adult or senile. New finds of Discosauriscus demonstrate the presence of external gills in specimens with skull lengths of up to 32 mm. On the base of this, together with the ornamentation of the skull roof bones and osteological features of new large specimens, it is here concluded that 1) Discosauriscus represents the larval, metamorphic and early juvenile stages of a reptiliomorph tetrapod, the adults of which are yet unknown and 2) two other discosauriscids (Ariekanerpeton and Utegenia) also represent early ontogenetic stages.