The fossil egg capsule Palaeoxyris – Indirect evidence of hybodontid sharks in the Late Paleozoic Remigiusberg Formation, Saar-Nahe Basin, Germany

The Remigiusberg lagerstaette is an outstanding fossil site with abundant and diverse aquatic and terrestrial biota from the base of the Rotliegend in the Saar-Nahe Basin, SW Germany. It refers to an about 50 m thick succession of fluvio-lacustrine sediments of the Remigiusberg Formation (Gzhelian–Asselian, Pennsylvanian–Permian boundary) that is exposed by an active quarry near Kusel, Rhineland-Palatinate. Between 2022 and 2023, during long-term excavations by the Urweltmuseum GEOSKOP, a total of six chondrichthyan egg capsule remains were found in paleotropical delatic mudstones of a silting distributary channel.

The compressed specimens, showing transverse rhombic pattern, are composed of eight bands, were originally about 55 mm long and 12 mm wide at their widest points. According to size, shape and banding characteristics they belong to the fossil chondrichthyan egg capsule morphotype Palaeoxyris. According to the size measurements, size ratios, pedicle shape with transverse band pattern, and the number, width and breadth pattern of the bands these specimens can be assigned to Palaeoxyris carbonaria, SCHIMPER 1850 (synonym = P. appendiculata). This is the most common Paleozoic Palaleoxyris species, known so far from the Late Carboniferous (Westphalian–Stephanian) of paleoequatorial Europe and North America. The capsules are assigned to hybodontid sharks as the most probable producers. Thus they indirectly prove their existence in the Remigiusberg ecosystem, while skeletal remains or teeth are absolute rarities. In addition, these new findings double the number of known shark egg capsule fossils from the Saar-Nahe Basin and increase the number of herein known Palaleoxyris specimens to eight.