Claudia Hildebrandt

Abstract Coprolites from the Rhaetian bone beds in south-west England can be assigned to crustaceans and fishes. Here, we report crustacean microcoprolites, including Canalispalliatum and Favreina, the first records from the British Rhaetian, from Hampstead Farm Quarry near Bristol, evidence for diverse lobsters and their relatives not otherwise represented by body fossils. Further, we identify five fish coprolite morphotypes that differ in shape (cylindrical, flattened) and in presence or absence of a spiral internal structure. Many coprolites show bony inclusions on the surface, often relatively large in proportion to the coprolite; these show little or no evidence for acid damage, suggesting that the predators did not have the physiological adaptations of many modern predatory fishes and reptiles to dissolve bones. CT scanning has revealed the nature, packing and identity of inclusions within the coprolites, mainly fish scales, and some coprolites can contain more than twenty. An extraordinary discovery in one coprolite comprises a single sculptured skull element of the large bony fish Severnichthys together with two caudal vertebrae of the marine reptile Pachystropheus: did the coprolite producer, likely a fish, scavenge some flesh from the head of Severnichthys and then bite off the tail of the reptile? Assigning coprolites to producers is difficult, but it seems that Gyrolepis was preyed on by nearly every predator. The faunas and trophic relations revealed by the coprolites show that this was a modern-style marine ecosystem, with abundant crustaceans and several species of durophagous fishes, evidence for an early stage in the Mesozoic Marine Revolution.

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.

The Late Triassic Rhaetian stage is perhaps best known in southwest Britain for the bone beds of the Westbury Formation, but there are other fossil-rich horizons within this and the underlying Blue Anchor Formation. Samples from a borehole drilled at the Filton West Chord, and collected from exposures near Bristol Parkway railway station, have yielded significant fossil material from both of these formations. The assemblage recovered from the Blue Anchor Formation is similar to those from the lower Westbury Formation, yielding roughly equal proportions of chondrichthyans and osteichthyans. Assemblages recovered from the Westbury Formation are typical of those from the upper Westbury Formation, in being dominated by osteichthyans. The borehole samples have produced the first recorded evidence of crinoids in the British Triassic, and the first evidence of coleoid cephalopods, in the form of grasping hooklets, from the Rhaetian, and indeed the first from the British Triassic.

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...