Article: Wenlock and Ludlow marine communities in Wales and the Welsh Borderland
C. E. Calef and N. J. Hancock
Five major marine benthonic communities, the (1) Salopina, (2) Homoeospira/Sphaerirhynchia, (3) Isorthis, (4) Dicoelosia, and (5) Visbyella communities occupied clastic sediments laid down in areas of increasing depth from the shoreline to deep areas in Wales and the Welsh Borderland during Wenlock and Ludlow times. The communities are described statistically and are shown to be completely intergrading in composition. They are dominated by epifaunal brachiopods, and so differ markedly from modern benthonic communities which are primarily infaunal. Other minor faunal associations are described.A species diversity gradient from low in the shallow-water Salopina community to high in the deep-water Dicoelosia community is analogous to modern benthonic diversity gradients. A density gradient running in the opposite sense suggests food was scarcer in deep water and thus important in determining brachiopod distribution. The Visbyella community probably lived at depths greater than the Dicoelosia community and represents the deepest limits of Silurian benthonic life.