Evolution of Silurian Brachiopod Communities along the Southeastern Coast of Acadia

Silurian rocks along the Atlantic coast from Massachusetts to Nova Scotia contain a diversity of level-bottom marine communities dominated by articulate brachiopods. Stratigraphic changes in these communities are classified as community evolution when there is a preponderance of continuous lineages between older and younger communities and community succession when there is not. In Nova Scotia, community succession within the near-shore environment was caused by faunal invasion between lower and upper Llandovery time, community successions accompanied offshore conditions during Wenlock time, and community evolution occurred within relatively constant nearshore conditions from late Wenlock through Pridoli time. Earliest nearshore communities of Nova Scotia were dominated by single species of pedunculate brachiopods, whereas later nearshore communities included greater diversity of both pedunculate and free-lying brachiopods. Late Silurian nearshore communities from Massachusetts to New Brunswick retained the pattern of single-species dominance, but species were of different stocks than those of early Silurian time and included free-lying as well as pedunculate forms.