Palaeoenvironment and taphonomy of the Hypsilophodon Bed, Lower Cretaceous Wessex Formation, Isle of Wight

The Hypsilophodon Bed occurs at the top of the Wessex Formation (Early Cretaceous, Barremian) on the Isle of Wight, southern England. Numerous remains of the small ornithopod dinosaur Hypsilophodon foxii have been recovered from the bed since the mid-nineteenth century. Previous theories for these fossil occurrences have focused on catastrophic mass death events, including miring and flood-related mortality. However, only limited sedimentological and taphonomic analyses of the horizon and its fossil assemblage have been undertaken, hindering efforts to evaluate different theories about how the assemblage formed. Here, we report a sedimentological study of the bed to constrain its depositional environment, an examination of the matrix from Hypsilophodon fossils to identify where they were collected from within the bed, and a taphonomic investigation of Hypsilophodon specimens. Our results indicate a floodplain environment, which later became a marsh and then mudflats at the edge of a lagoon. Hypsilophodon fossils are spatially and stratigraphically distributed throughout the bed. The specimens are largely incomplete and unabraded, suggesting that most perished on, or near to, the floodplain and may have lain exposed for some time prior to burial. Overall, the evidence suggests that the fossil assemblage of the Hypsilophodon Bed formed as an accumulation of remains over time.