Microvertebrates from the classic Rhaetian bone beds of Manor Farm Quarry, near Aust (Bristol, UK)

Manor Farm Quarry shows a detailed record of the entire Rhaetian section typical of southwest England. It has yielded a standard Rhaetian marine fauna, including eight species of sharks, four species of actinopterygian fishes, and the reptiles Pachystropheus and Ichthyosaurus, all of which are widely known from coeval sites. An unusual feature is the occurrence of an unidentified coelacanth, represented by nine isolated quadrates showing a broad range of sizes. The site has also provided information on the occurrence of vertebrates through five distinctive bone-bearing horizons, including the famous basal Westbury Formation bone bed, as well as a second horizon with bones at the top of the Westbury Formation, and three within the overlying Cotham Member of the Lilstock Formation. These show substantial differences, especially between the basal bone bed and the four overlying bone-rich units. The basal Westbury Formation bone bed is dominated by shark remains (73%, compared to 23-30% in the four overlying units), most notably, teeth of Rhomphaiodon minor and Lissodus minimus, which are absent or rare in higher beds. Further, teeth of the bony fishes Gyrolepis albertii and Severnichthys acuminatus are rare in the basal bone bed, but abundant at the top of the Westbury Formation and through the Cotham Member, and the sharks Duffinselache holwellensis and Pseudocetorhinus pickfordi, absent in the basal bone bed, are relatively abundant in the four overlying bone-bearing units. These differences in faunal lists and in relative proportions probably do not reflect sampling, but some major differences in ecology and evolution.