The general history of the Orthida in the GIOR is in accordance with the general tectonic and faunal history of the region established by earlier authors (Cocks and Torsvik 2002). Even though endemic rates and ordination analysis targets two different aspects of the faunal data they can be compared and support each other – or conversely indicate that the results of the analyses are uncertain.

The faunal data can be divided into three segments based on the overall association trends of the analyses: The 1^st segment includes the Early-Middle Ordovician, where the old Gondwana marginal terranes of Baltica and later Avalonia changed faunal content to develop a more mixed composition between the equatorial terranes and the polar to high latitude Gondwanan terranes. At the same time there was a dramatic diversification and geographical expansion among the orthides (Harper and Gallagher 2001; Harper and Mac Niocaill 2002), which was truncated by an Abereiddian-Llandeilian diversity reduction and an increase in endemism. This diversity reduction may have been the result of a contraction in available living space caused by a regression during the Arenig (Barnes et al. 1996). From the Early Ordovician, the European massifs formed their own faunal association, with Armorica and Iberia forming a tight link, which is in accordance with the conclusions of Cocks and Torsvik (2002); these authors included Iberia with Armorica, except the South Portuguese Zone where the oldest rocks are of Middle Devonian age (Cocks 2000). Note that the faunal association of the European massifs may not be restricted to these, as the analysis presented here does not include all the plates in the neighborhood of the European massifs.

The 2^nd segment (Figure 5) was initiated during the Costonian with the singularly largest diversity increase for most of the plate groups investigated. During the 2^nd segment, Baltica, Avalonia and Laurentia consolidated as a coherent faunal association independent of the peri-Gondwanan European massifs and core Gondwanan terranes, creating a gradient that correlates roughly with palaeolatitude (Torsvik 1998; Cocks and Torsvik 2002). Three distinct faunal associations formed, however, note that neither analytical method presented here provides a measure of the physical distance between the plates.  The 3^rd segment (Figure 6) covers the Silurian, during which the overall faunal association pattern changed rapidly as a result of the Late Ordovician extinction event, forming a more or less homogenous faunal association during the early parts of the Llandovery.

This homogenous association gradually differentiated, however, perhaps as a result of the core Iapetan plates moving towards Gondwana during the Silurian, the same degree of faunal provincialism as evidenced during the Middle-Late Ordovician was never re-established. At the Lower-Middle Silurian boundary, two distinct faunal associations emerged from the supergroup, forming a (within the region) cosmopolitan low-mid latitude fauna and a high latitude fauna (Clarkeia fauna, see Fortey and Cocks 2003). Furthermore, the apparent isolation of Siberia indicates a separate faunal association of this plate.

During this interval the European massifs retained their faunal integrity, however, Bohemia changed from being associated with the massifs to the larger Gondwanan-Iapetan association, indicating movement of this terrane. These conclusions are tentative however, being hampered by very low Silurian diversities, which add uncertainty to the results of the analyses.

Siberia

Siberia is highly mobile throughout the analyses, which is partly the result of low diversities during the earlier and later temporal intervals analyzed. The Siberian orthides appear to be of a mixed association, including both Gondwanan and Laurentian elements, which causes the spurious placement in the dendrograms (Figure 3). The relationship of Siberia with the other GIOR plates is clearer in the NMDS diagrams (Figure 4), where it is initially shown with a placement near Laurentia and South America, however, during the Late Ordovician Siberia became progressively more affiliated with the core Iapetan plates, retaining, however, a distinct faunal signal. The Late Ordovician extinction event possibly affected the Siberian faunas differently than the Laurentian as seen in the placement of Siberia in the Rhuddanian NMDS diagram (Figure 4, bottom left). A tentative link with the Silurian Gondwanan-Iapetan faunal association was, however, retained during the entire Silurian. This pattern is consistent with other faunal data (Nikiforova and Andreeva 1961) and is repeated for groups like trilobites (Chugaeva 1973). These faunal data suggest that Siberia was at least in partial faunal contact with Laurentia during the Silurian, this distance being smaller than the distance to the North China Plate, whose influence was apparently less; during the Early and Early-Middle Silurian the fauna remained a tropical pandemic (Fortey and Cocks 2003).

The Precordillera

This terrane is also highly mobile in the cluster and ordination diagrams presented here, owing both to changing compositions in the faunal data and low diversities. Orthide data support a Laurentian origin for the Precordillera. During the Arenig, 15 genera are reported from the Precordillera. With the exception of Monorthis, the Precordilleran genera were all found on Laurentia. Monorthis is reported from the Early Ordovician only from Wales (Avalonia) and Argentina (the Precordillera). This is in accordance with Fortey and Cocks (2003), who noted an Avalonian influence in the faunas. Apart from Argentina, orthides are reported from Bolivia, Brazil and Colombia within South America. These records are unfortunately much more fragmented than those from Argentina. There are five genera recorded from Arenig deposits of these countries, and none of these is found on the Precordillera, however, for example Acanthorthis and Orthidium are shared between the Precordillera and Laurentia. This lends to support for Precordillera origin within Laurentia as proposed by Thomas (1991); Astini et al. (1995); Davis et al. (1997) and Gerbi (1999).

The orthides of the Middle-Late Ordovician from the Precordillera are commonly widespread to cosmopolitan. The orthide data, therefore, cannot be safely used to delineate the position in time and space of this terrane during the Late Ordovician – faunal data from other groups needs to be employed.

Bohemia (Perunica)

A greater amount of orthide data are known from the Ordovician-Silurian of Bohemia, than from any other peri-Gondwanan terrane, due to the studies of the Bohemian successions in the Prague Basin, especially by authors such as Barrande in the 19^th century and more recently by Havlíček (Havlíček 1977; Havlíček et al. 1994). During the Early-Middle Ordovician, Bohemia obviously formed part of the European massif association, supporting the conclusions of Fortey and Cocks 2003. As indicated by the cluster analysis, the European massifs remain more closely related to each other than any other plate or plates during the entire Ordovician, and only by the Middle Silurian does Bohemia switch association (Figure 3, bottom right). During the Caradoc, ordination plots indicate, however, that Bohemia was that of the European massifs most closely associated with the Iapetan and Gondwanan plates (Figure 4), a situation which developed during the Caradoc-Ashgill.

The orthide data confirm the conclusions of Fortey and Cocks (2003), who summarized trilobite and brachiopod data from Bohemia, and noted that the terrane was probably close to, however, perhaps tectonically separate from West Gondwana by the Tremadoc. Greatest oceanic separation was achieved during the Caradoc, followed by an interval when Bohemia drifted progressively closer to Baltica.