CT-based re-evaluation of the anatomy and phylogeny of the trematopid temnospondyl Rotaryus gothae

Trematopids are a monophyletic group of Permo-Carboniferous dissorophoid temnospondyls from North America and Europe. These anamniotes were well adapted for a terrestrial lifestyle, but most species are only known from a single specimen. The scarcity of well-preserved fossils, combined with anatomical variation among taxa, poses significant challenges for resolving trematopid taxonomy and relationships. This study re-evaluates Rotaryus gothae, a trematopid from the lower Permian Bromacker locality in central Germany, using computed tomography (CT) and 3D digital segmentation. This detailed examination revealed previously obscured anatomical features and led to the identification of novel characters. Notable findings include the presence of an internarial fenestra and new insights into the mandibular and palatal anatomy, including new information on the dentition. Furthermore, a comprehensive set of postcranial elements was uncovered, including a previously unknown, nearly complete and articulated right hindlimb. These discoveries provide valuable new insights into the locomotor morphology and functional anatomy of Rotaryus gothae. Bayesian and parsimony analyses were conducted using two matrices, respectively. The results support the trematopid identification ofRotaryus, but it acts as a wildcard taxon with varying phylogenetic positions depending on dataset and method used. Furthermore, the broader relationships within Olsoniformes remain unresolved. This new data has led to a better anatomical understanding of Rotaryus but also highlights the difficulties posed by limited specimen availability and high morphological variability. This study underscores the necessity of re-evaluating early tetrapods with modern tools to refine unresolved phylogenetic questions and provide a foundation for future investigations.