An unusually large ‘suspension-feeding’ fish from the Kimmeridge Clay Formation of Dorset: the first true record of Asthenocormus (Pachycormiformes: Asthenocorminae) in the UK

A partial caudal fin of a large-bodied asthenocormine pachycormiform (Pachycormiformes: Pachycormidae: Asthenocorminae) is described from the Upper Jurassic (lower Tithonian) Kimmeridge Clay Formation of Dorset, England. The specimen comprises associated fin rays, basal fulcra, ‘epurals’ and paired pre-caudal scutes, the combination and morphology of which is consistent with the large (2–3 m TL) edentulous, supposedly ‘suspension-feeding’ asthenocormine, Asthenocormus titanius (Wagner), presently known only from the Upper Jurassic plattenkalks of Bavaria, Germany. Asthenocormus has previously been documented in the literature as being present in the Middle and Upper Jurassic of England, however all of these specimens have been misattributed or since referred to different genera. However, the specimen from the Kimmeridge Clay Formation is here referred with confidence to Asthenocormus. Morphological variation in the pre-caudal dorsal scute of the new specimen compared to the Bavarian material suggest that the Kimmeridge Clay specimen likely represents a new species of Asthenocormus, although it is currently too poorly represented to diagnose, and hence we refer the specimen to Asthenocormus cf. titanius. The new specimen represents the first true record of Asthenocormus from the UK, thereby extending its known palaeobiogeographic distribution and further demonstrating faunal similarities between fish assemblage from the Kimmeridge Clay Formation of Dorset and the Solnhofen-type plattenkalks of southern Germany. Additional comments are also made on the hidden diversity of pachycormid fishes in the Kimmeridge Clay Formation.