Microvertebrates from the basal Rhaetian Bone Bed (latest Triassic) at Aust Cliff, S.W. England

Abstract

The famous Aust Cliff section, on the east bank of the River Severn, S.W. England, includes one of the first documented successions through the Rhaetian stage (latest Triassic) and a classic Triassic-Jurassic boundary section, and, historically, the first ever mention and description of the Rhaetian bone bed, dating back to the 1820s. The larger fossils, abraded vertebrae and limb bones of marine reptiles, have been widely reported, but the microvertebrates from the Aust Cliff Rhaetian basal bone bed have been barely noted, after the classic works of Louis Agassiz, who named 17 fish taxa from Aust in the 1830s, of which eight are still regarded as valid taxa. Here we describe the extensive microvertebrate fauna, including six species of chondrichthyans identified from their teeth, featuring the second ever report of Parascylloides turnerae from the UK, as well as numerous examples of three morphotypes of chondrichthyan placoid scales (denticles). In addition, we report four species of osteichthyans based on their teeth, Gyrolepis, Severnichthys, Sargodon, and Lepidotes, as well as numerous isolated scales, fin rays, and gill rakers, and the second occurrence of cephalopod hooklets from the British Rhaetian. Four types of coprolites are noted, probably produced by these fishes, and these, with evidence from teeth, allow us to present a food web for the classic Rhaetian bone bed seas.