Larval ontogeny of Micromelerpeton credneri (Temnospondyli, Dissorophoidea)

A growth series of 97 specimens of the dissorophoid temnospondyl Micromelerpeton credneri from the Permo-Carboniferous of Central Europe is taken as a basis for ontogenetic investigations. Whereas the dermal skull roof is already ossified and sutured in the smallest specimen with a skull length of 6 mm, the ossification sequence of the postcranium can be reconstructed. Compared to branchiosaurids and Recent urodeles, the ossification of the post-cranial skeleton is delayed. For the first time, external gills are described in Micromelerpeton credneri. Their three pairs of branches shorten proportionally during ontogeny. A Cartesian transformation and biometric analyses show allometric changes in the dermal skull roof Whereas the preorbital region elongates slightly (due to positive allometric growth of nasal length and negative allometric growth of orbits) and grows in width isometrically, the postorbital skull table shows isometry in length (due to positive allometry of frontal length and negative allometry of parietal length) and distinct negative allometry in width (due to negative allometry of parietal and supratemporal width). The interorbital width relatively decreases. The cheek region shows positive allometry both in length and in width, shifting the jaw articulation posteriorly. In this way proportionally more space and attachment area for the adductor musculature are provided and the gape enlarges proportionally. The positive allometric growth of the diameter of the sclerotic ring indicates increased importance of the optical sense. Transformation into the adult stage took place gradually and in a longer period of time during ontogeny than in extant amphibians.