The Ordovician brachiopod radiation: Roles of alpha, beta, and gamma diversity
Published:April 01, 2010
The Ordovician Period (ca. 488–444 Ma) witnessed profound changes in the biodiversity and biocomplexity of marine life, marked by the installation of a benthos dominated by suspension-feeding animals, most notably the brachiopods. The Ordovician brachiopod fauna was dominated by rhynchonelliformeans in contrast to that of the underlying Cambrian System, characterized by a diversity of various non-articulated groups. Over an interval of some 25 m.y., accelerating γ (inter-provincial), β (inter-community), and α (intra-community) diversity was initiated by high diversities among Early Ordovician brachiopod faunas associated with the dispersal of the continents and the high frequency of volcanic arcs and microcontinents (γ diversity). During the Early and Middle Ordovician, community types expanded particularly into deeper water and around carbonate platforms and structures (β diversity). Moreover, during the period the α diversity of individual assemblages increased from <10 species during the Late Cambrian to ~30 in the Late Ordovician, with the canalization of ecological niches and the opportunity for more densely packed communities. The end-Ordovician extinction event was a severe crisis for the more common Ordovician taxa, the orthide and strophomenide brachiopods. Whereas some widespread taxa, characteristic of deep-water environments, survived, many from shallower-water, together with those from the deep shelf and slope, disappeared. The subsequent Silurian fauna became increasingly dominated by atrypide, athyridide, spiriferide, and rhynchonellide brachiopods.