New material of the reptile Colobomycter pholeter (Parareptilia: Lanthanosuchoidea) and the diversity of reptiles during the Early Permian (Cisuralian)

Over 150 years of collecting in the Permian Basin of North America suggests that reptiles evolved in the shadows of Dimetrodon and related Early Permian synapsids. Research in recent decades has revealed an unappreciated ecological diversity in addition to taxonomic richness of Early Permian reptiles and recognition of a radiation of Palaeozoic-Triassic forms now known as parareptiles. Perhaps the most unusual parareptile to be described from the Permian Basin of North America is the lanthanosuchoid Colobomycter pholeter from the Richards Spur locality, Oklahoma, USA. Although initially described as a synapsid, this species was later reassigned to Parareptilia. Colobomycter is very distinct from all other known parareptiles, and coeval tetrapods in general, largely due to its extremely conspicuous and unique marginal dentition. The single, very large anteriormost tooth of the premaxilla and the paired enlarged teeth of the maxilla characterize the dentition of Colobomycter. Herein we describe new cranial material of C. pholeter that reveals previously unknown aspects of the skull and further increases our anatomical knowledge of this unique taxon. The new cranial data allow us to reassess the interrelationships of Early Permian parareptiles, which has critical implications for the diversity of parareptiles during the Early Permian. Parareptiles were a diverse clade of reptiles that were an important component of Middle and Late Permian ecosystems, having gained a cosmopolitan distribution by the Middle Permian. In contrast to their diversity during the Middle and Late Permian, parareptiles were historically considered to have a lower taxic diversity during the Early Permian, as well as being rare members of Early Permian fossil assemblages. However, with the numerous species that have been produced from the Richards Spur locality of Oklahoma in recent years, we now have a much better view regarding the diversity of parareptiles during the Early Permian, with their diversity coming close to matching that of Early Permian eureptiles. Richard Spur is also unique in that more than half of all known Early Permian parareptiles are found there, as well as in capturing representatives of all major lineages of terrestrial parareptiles present during the Early Permian.