THE COMPOSITION AND STRUCTURE OF LOWER SILURIAN MARINE COMMUNITIES

Authors


Abstract

Five benthic communities occupied the shelf regions of the British Isles, Norway, and North America in Upper Llandovery times. The communities are listed below in order of increasing distance from shore.

  • 1The Lingula Community is the least diverse; it has both infaunal elements, including a protobranch, and two lingulids, and epifaunal elements, including a rhynchonellid, a pterioid, and a cornulitid. A restricted and protected near-shore environment, such as a bay or estuary, is postulated.
  • 2The Eocoelia Community shares elements in common with the former community, but is more diverse and is dominated by epifaunal forms; the many small pedunculate brachiopods probably lived attached to the large leptostrophiid brachiopod.
  • 3The Pentamerus Community is dominated by this genus which lived free and upright on the bottom; smaller pedunculate brachiopods probably attached to this large neighbor.
  • 4The Costistricklandia Community was similar in structure to the former community with the many small pedunculate brachiopods being attached to the large Costistricklandia.
  • 5The Clorinda Community is the most diverse, with a great variety of small brachiopods which were probably able to attach to small objects in this quiet off-shore environment, or to some moderately sized brachiopods, such as Clorinda and Cyrtia, which apparently lived free on the bottom.

The brachiopod dominated communities of the Silurian clearly inhabited the ‘level bottom’, an area now occupied mainly by infaunal forms. The main attachment surfaces for the epifaunal elements of the Silurian communities were disarticulated, convex-upward shells.

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