The stratigraphically oldest eryopoid temnospondyl from the Permo-Carboniferous Saar-Nahe Basin, Germany

An isolated mandible of a large temnospondyl from Theisbergstegen, Rhineland-Palatinate, is described that is derived from the Late Carboniferous Remigiusberg Formation of the Saar-Nahe Basin, southwestern Germany. The mandible is well preserved and exposed in lingual view, showing typical characteristics of basal eryopoids (i.e., eryopids plus stereospondylomorphs) such as the small size of the postglenoid area formed by the surangular and articular and the rather small Meckelian fenestra that fails to contact the postsplenial. It can be distinguished from the mandibles of all other known eryopoids from the Saar-Nahe Basin by characters such as a distinctly higher surangular process, higher, more strongly curved marginal teeth and the presence of a symphyseal lamina with at least one large parasymphyseal tooth. The mandible resembles those of eryopids rather than stereospondylomorphs in the angle of jaw being located on the level of the anterior portion of the surangular process and the dorsal edge of the mandibular ramus being dorsally concave. The described mandible is unequivocally the earliest known eryopoid from the Saar-Nahe Basin and shows that also large temnospondyls invaded the lakes of the Saar-Nahe Basin already during the "Remigiusberg invasion" in the Late Carboniferous.