The last eryopids: Clamorosaurus and Syndyodosuchus from the late Kungurian (Cisuralian, Permian) of Russia revisited

The three Permian (Cisuralian) temnospondyls Syndyodosuchus tetricus , Clamorosaurus nocturnus and C. borealis from the Pechora Coal Basin in Russia, are redescribed. The assignment of Clamorosaurus to the Eryopidae is confirmed, and several new characters are presented in detail. Syndyodosuchus tetricus is identified as an eryopid for the first time, as this taxon was previously regarded as a basal stereospondylomorph. In our phylogenetic analysis, S. tetricus forms a polytomy at the base of the Eryopidae together with Actinodon frossardi and Osteophorus roemeri . More crownward, Glaukerpeton avinoffi and Onchiodon labyrinthicus build a polytomy, followed by O. thuringiensis and Stenokranio boldi as successive sister taxa of a monophyletic Clamorosaurus plus Eryops megacephalus . A reweighted analysis finds A. frossardi at the base of Stereospondylomorpha; the Eryopidae is completely resolved and consists of S. tetricus , O. roemeri , G. avinoffi , O. labyrinthicus , O. thuringiensis , S. boldi and E. megacephalus as successive outgroups to Clamorosaurus . The phylogenetic position of Clamorosaurus among the most derived eryopids is congruent with its young stratigraphic age, whereas for S. tetricus as a basal eryopid a long ghost lineage has to be assumed. Although being coeval, the two genera occurred in different environments, with Clamorosaurus being preserved in lacustrine limestones wheras S. tetricus was found in a coal bed. The lifestyle of these eryopids can best be designated as semi-aquatic.