New anatomical details concerning the cranial structure of the early Permian stem reptile Protorothyris archeri revealed by μCT , with implications for the evolution of olfaction in reptiles

Abstract Re‐examination of early‐diverging stem reptiles can provide valuable phylogenetic data and insights into the evolution of sensory systems during the terrestrialization of tetrapods in the late Palaeozoic. Here, we apply μCT imaging to a previously undescribed specimen of Protorothyris archeri . Our segmentations revealed previously unknown anatomical details of this species, including enlarged dentary teeth, denticles on the parabasisphenoid, and the morphology of the internal surfaces of the dermatocranial elements. We included this specimen within a phylogenetic matrix of 177 operational taxonomic units and 628 morphological characters designed to examine the relationships of early‐diverging amniotes, particularly stem reptiles. Bayesian and parsimony analyses reveal that there is still topological discordance among some clades (e.g. caseasaurs, varanopids), although these analyses confirm that ‘protorothyridids’ do not form a clade, consistent with other recent phylogenetic analyses. The position of P. archeri as an early‐diverging stem reptile in our analyses suggests that it may provide insight into the evolution of the olfactory system as the reptile lineage diversified throughout the Permian, based on the morphology of the cristae cranii. However, more anatomical work is needed to determine if the depth of the cristae cranii is indicative of olfactory bulb size and capability.