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Abstract The Upper Carboniferous protorothyridid amniote Brouffia orientalis from Czech Republic is redescribed. Photogrammetric scanning of the holotype and only known specimen yields considerable new information on the skull and postcranium of this tetrapod and allows us to amend previous morphological descriptions to a substantial degree. A virtual 3D model built from photogrammetry scan data is used as the basis for a new reconstruction of the skull in dorsal, lateral, and ventral aspects and the lower jaw in lateral aspect. We expand and refine the diagnosis of Brouffia and compare it with other protorothyridids. We discuss the affinities of this taxon by coding it in a recently published data matrix of early amniotes, which we subject to maximum parsimony and Bayesian fossilized birth–death analyses. Brouffia emerges as the sister taxon to Coelostegus in all analyses, but the position of these two taxa within amniotes varies. In a parsimony analysis with unweighted characters, the (Brouffia + Coelostegus) clade forms the sister group to Synapsida. In various experiments of character reweighting, that clade is placed crownward of Captorhinidae on the stem-group of Reptilia, but anticrownward of remaining protorothyridids. The latter constitute either a paraphyletic array relative to Diapsida or their monophyletic sister group. The Bayesian analysis retrieves (Brouffia + Coelostegus) as the most basal plesion on the stem-group of Reptilia.

We redescribe the holotype and only known specimen of the early eureptile Coelostegus prothales from the Upper Carboniferous of the Czech Republic using photogrammetric scanning and a virtual 3D rendition of its skull. New information is available on several skull and lower jaw bones, including the postorbital, supratemporal, tabular, postparietal, angular, and prearticular. The new data also permit the correct identification of previously undetected or mis-identified elements (e.g., supratemporal; quadratojugal; angular). We provide an amended diagnosis of Coelostegus and a new reconstruction of the skull in dorsal and lateral views. To evaluate the affinities of Coelostegus, we code this taxon in two recently published taxon-character matrices. Parsimony and Bayesian analyses do not permit firm conclusions on the phylogenetic position of Coelostegus or, indeed, the status and extrinsic relationships of protorothyridid amniotes. Coelostegus emerges either as the sister taxon to the recently redefined Diapsida (Araeoscelidia; Varanopidae; Parareptilia; Neodiapsida), as one of the most basal protorothyridids, or as a derived stem-group amniote in various parsimony-based analyses, or as the basalmost protorothyridid in one Bayesian analysis, with protorothyridids forming a paraphyletic array relative to Diapsida. We review the cranial similarities and differences between Coelostegus and other protorothyridid genera and discuss the implications that various phylogenetic results have for our understanding of early amniote relationships.