This study indicates that five important developments affected faunal organization of the orthides of the greater Iapetus region: 1) the diversification of the Early Ordovician, 2) the Middle Ordovician diversity reduction, 3) renewed diversification of the early Caradoc, 4) the Hirnantian glaciation and 5) the following gradual homogenization of the faunas during the Silurian. The conclusions agree with the general plate tectonic history presented for the GIOR presented in recent reconstructions such as those of Cocks and Torsvik (2002) and Torsvik and Rehnström (2003).

The high degree of correspondence between the palaeogeographic maps for the greater Iapetus region and the results of the ordination/cluster analysis presented here lends credibility to the use of these methods in palaeobiogeography. However, it remains unresolved which similarity/distance measures that should be used for the calculations and if and how these should be modified to accommodate differences across environmental gradients.

This study indicates that a combination of indices is necessary to find the strongest faunal signals. Plates such as Siberia and the Precordillera will remain problematic because their faunal signals are mixed, however, this can perhaps be resolved with the appliance of data from other groups (Fortey and Cocks 2003). Moving from the type of generalized study presented here, the next logical step would be to distinguish between intra-cratonal/marginal locations or even individual biofacies. Furthermore, the important intra-oceanic terranes and islands of the Celtic province should be separated (Harper and Mac Niocaill 2002). This separation would add a further level of precision to the analyses presented here.