Cranial Anatomy, Ontogeny, and Relationships of the Late Carboniferous Tetrapod Gephyrostegus bohemicus Jaekel, 1902

ABSTRACT We review the cranial morphology of the Late Carboniferous terrestrial tetrapod Gephyrostegus bohemicus from the coal deposits of the Nýřany Basin in the Czech Republic. Gephyrostegus is known from several skulls ranging in length from about 25 mm to about 58 mm (holotype). The narrow skull is about twice as long as wide and shows a well-ossified quadrate and articular, but no evidence of braincase ossification. Autapomorphic features include a pustular ornamentation on some skull table bones, and a plate-like tabular process exhibiting a fine dorsal pitting. Gephyrostegus shares with Bruktererpeton fiebigi (Late Carboniferous, Germany) the presence of low, anteromedially to posterolaterally orientated sharp ridges on the posteroventral surface of the vomer. It shares with seymouriamorphs a rectangular, transverse pterygoid process and closely packed, radially arranged rows of small denticles on the palate. A phylogenetic analysis retrieves Gephyrostegidae (Gephyrostegus, Bruktererpeton) as sister group to Seymouriamorpha, although this wider clade receives low bootstrap support.