A new species of Cyclotosaurus (Stereospondyli, Capitosauria) from the Late Triassic of Bielefeld, NW Germany, and the intrarelationships of the genus

Abstract. A nearly complete dermal skull roof of a capitosaur stereospondyl with closed otic fenestrae from the middle Carnian Stuttgart Formation (Late Triassic) of Bielefeld-Sieker (NW Germany) is described. The specimen is assigned to the genus Cyclotosaurus based on the limited contribution of the frontal to the orbital margin via narrow lateral processes. A new species, Cyclotosaurus buechneri sp. nov., is erected based upon the following unique combination of characters: (1) the interorbital distance is short so that the orbitae are medially placed (shared with C. robustus); (2) the region lateral to the orbitae is only slightly broader than the orbitae (shared with C. posthumus, C. ebrachensis, C. intermedius, and C. mordax); (3) the postorbital region is slender (shared with C. ebrachensis); (4) the preorbital projection of the jugal is shorter than half the length of the snout (shared with C. mordax, C. ebrachensis, C. intermedius, C. posthumus, and C. hemprichi). A phylogenetic analysis of seven Cyclotosaurus species, including C. buechneri, and eight further capitosaur taxa with the Rhinesuchidae as an outgroup finds a monophyletic Cyclotosaurus. In accordance with its stratigraphic occurrence, C. buechneri nests at its base but is more derived than C. robustus. Among the more derived Cyclotosaurus species, C. ebrachensis and C. intermedius, as well as C. posthumus and C. hemprichi, form sister groups, respectively. However, the phylogenetic position of C. mordax with respect to both groups remains unresolved. In the phylogenetic analysis presented here, Cyclotosaurus is the sister group of the Heylerosaurinae (Eocyclotosaurus + Quasicyclotosaurus). Cyclotosaurus buechneri represents the only unequivocal evidence of Cyclotosaurus (and of a cyclotosaur in general) in northern Germany.