The late Viséan Chemnitz fossil site – a Carboniferous locality full of surprises

Besides the Early Permian Fossil Forest, for which Chemnitz is known in the palaeontological literature worldwide, temporary outcrops in the north of the city have yielded a rich fauna and flora from the late Early Carboniferous. 19th- and early 20th-century sandpits and a motorway construction site in the early 2000s allowed for insights into the Ortelsdorf and Berthelsdorf Formations of the Hainichen basin (330 ± 4 Ma for the upper Ortelsdorf Fm). Characterised by loose sandstones, thin coal seams, carbonatic siltstones and locally thick conglomerates with large boulders, these formations document frequent changes of braided-river, swamp and alluvial plain conditions. The sandstones preserve a diverse flora consisting of mosses, horsetails, ferns, seedferns, and lycophytes, a terrestrial arthropod assemblage comprising myriapods, trigonotarbid and phalangiotarbid arachnids, scorpions, and Arthropleura, aquatic arthropods and vertebrates including chondrichthyans, possible actinopterygians, sarcopterygians, and Germany‘s oldest tetrapod. Most remarkably, the chondrichthyan record involves two types of shark egg capsules – Fayolia sterzeliana and Palaeoxyris sp. – which in places occur on the same bedding plane, and a xenacanth cephalic spine that probably derives from the producer of the Fayolia capsule. No further remains belonging to xenacanths or hybodonts correlative with the Palaeoxyris capsules have been found so far. Nonetheless, the Chemnitz locality represents the oldest record of chondrichthyan egg capsules worldwide and the only site where two types of capsules not only co-occur in the section, but actually are found on the same surface, indicating nearly synchronous deposition by two different groups of producers in the vegetated nearshore area.