First occurrence of an acipenseriform (Chondrostei: Acipenseriformes) from the Upper Jurassic Kimmeridge Clay Formation of England

Abstract

ABSTRACT Several fragmentary remains of an enigmatic acipenseriform, the order of fishes that includes living sturgeons and paddlefishes, are described from the Upper Jurassic Kimmeridge Clay Formation of southern England. These remains are significant because they represent the first definitive evidence of an acipenseriform from the Upper Jurassic described outside of Asia. In total, five associated dorsal caudal fulcra from the caudal fin and a paired pelvic fin from at least two separate individuals are identified as acipenseriform, although it is uncertain to which family they belong. Three families of Mesozoic acipenseriform are considered: the †Chondrostei (Lower Jurassic, Europe), the †Peipiaosteidae (Upper Jurassic to Lower Cretaceous, Asia), and the extant Acipenseroidei (Lower Cretaceous–recent, Laurasia). The new Kimmeridgian Clay acipenseriform fossils would significantly extend the temporal and spatial distribution of whichever family they are ascribed, but their affinities remain unclear. Regardless, the stratigraphic and paleobiogeographic occurrence of the new specimens holds novel implications for the poorly known evolutionary history of this primitive clade of extant non-Neopterygian fishes.