A taxonomic and paleoecological review of the Rhaetian chondrichthyan fauna of Bonenburg (NRW) Germany

Abstract The chondrichthyan fauna of the Late Triassic Rhaetian is fairly diverse and has been well-studied in France and the United Kingdom. Conversely, contemporaneous faunas from Germany only were sporadically analyzed. Here, we present a taxonomic and palaeoecological evaluation of a cartilaginous fish assemblage from Bonenburg in NW Germany, which is represented by isolated teeth as well as cephalic and dorsal fin spines. This material includes the first holocephalan record as well as several morphotypes of dorsal fin and cephalic spines. Based on the material from Bonenburg, Rhomphaiodon minor is synonymized with Nemacanthus monilifer and assigned to the Palaeospinacidae. The Bonenburg bone beds differ from other localities across the Rhaetian Sea as Nemacanthus monilifer is present in unprecedented numbers and Lissodus minimus , typically the most common shark species in Rhaetian deposits, is a distant second in abundance. This, as well as other comparative measurements of Rhaetian shark diversity, reveal that neoselachians were a larger component of Rhaetian ecosystems than previously assumed. A food web reconstruction with a focus on the chondrichthyan and actinopterygian taxa present at the locality shows a general partitioning of niches among the chondrichthyans of Bonenburg, and that chondrichthyans inhabited all but the lowest and highest positions in the trophic chain, revealing that they were an important and ecologically diverse part of their ecosystem.