The Rhaetian (Late Triassic) vertebrates of Hampstead Farm Quarry, Gloucestershire, UK

The Rhaetian marine transgression, which occurred across Europe in the latest Triassic, 205.5 Ma, famously deposited one or more bone beds. Attention has generally focused on the basal bone bed alone, but here we explore this bed, and a stratigraphically higher bone bed at the top of the Westbury Formation, and compare the faunas. The Rhaetian at Hampstead Farm Quarry, Chipping Sodbury, Gloucestershire, UK, has produced more than 26,000 identifiable microvertebrate remains, including teeth and scales of chondrichthyan and osteichthyan fishes, as well as vertebrae of sharks, bony fishes, ichthyosaurs, and plesiosaurs. The higher bone bed (‘bed 9’) contains more small specimens than the basal bone bed, and they are also less abraded, suggesting less transport. Both bone beds yield largely the same taxa, but Rhomphaiodon minor and rare Vallisia coppi and Sargodon tomicus are found only in the basal bone bed. Duffinselache is reported only from units above the basal bone bed, but low in the Westbury Formation, and durophagous teeth only from two horizons. Four out of nine chondrichthyan species are common to both bone beds, whereas Rhomphaiodon minor and Ceratodus are absent, and hybodonts in general are rarer, in bed 9. Bed 9 is the richer source of marine reptile remains, including ichthyosaur teeth, jaw fragments, vertebrae, rare plesiosaur teeth and vertebrae, and a few Pachystropheus vertebrae and limb bones. Whereas the basal bone bed represents considerable transport and possible storm bed deposition associated with the onset of the Rhaetian Transgression, bed 9 was deposited under a lower energy regime.