The ecology of a Middle Jurassic hardground and crevice fauna

The base of the Bradford Clay (Bathonian) at Bradford-on-Avon, Wiltshire, was a hardground. Soft lime-sand below the hardground was washed out to form crevices, the walls and the floor of which also became lithified. The hardground and the crevices were colonized by encrusting and boring organisms, which polarized into: (i) an upper-surface community dominated by oysters, Apiocrinus and Nubeculinella and (ii) a crevice community, dominated by Serpula (Cycloserpula), encrusting ectoprocts, and Moorellina. Similar ecological distributions are known from other formations, and are attributed to differences in light and turbulence, which in turn influenced competition for space and food.