Analysis of Orthida (Brachiopoda) spatio-temporal data from a new database indicates that five major developments controlled the faunal provincialism of the Orthida in the Greater Iapetus Ocean during the Ordovician-Silurian. These developments include: 1) A diversification during the Early Ordovician; 2) a diversity reduction during the Middle Ordovician, followed by; 3) renewed diversification during the early Caradoc; 4) the Hirnantian glaciation; and 5) a gradual homogenization of the faunas during the Silurian, despite some increasing endemism. The orthides of the peri-Gondwanan European massifs may have formed a faunal association, distinct from the fuanas of the Iapetan central area, whereas the general pattern of faunal associations appears to be related to palaeolatitude and the relative positions of the palaeoplates. The observed faunal patterns generally support recent plate tectonic reconstructions.

Anders Tychsen. Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark.
David A.T. Harper. Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark.