A total of 11 plates from the entire GIOR were included in the study. These were the Gondwanan South America and Africa (there are no Ordovician orthide data from Antarctica), the peri-Gondwanan European massifs: Bohemia (Perunica), Apulia, Iberia and Armorica and the core Iapetus Ocean terranes of Laurentia, Siberia, Baltica and Avalonia. Additionally the Precordillera was included (see below). We generally have used the newest data available (e.g., Cocks and Torsvik 2002; Stampfli and Borel 2002) to outline the borders of these terranes with respect to the placement of orthide data on the various plates.

Most of these did not entail problems, however, it is important to note that this study is based on data from a global database, applied to a regional scale area. This means that some problems such as the tectonic history of the "exotic" blocks of the Holy Cross Mountains (HCM) of Poland have not been resolved in this study (Belka et al. 2002; Cocks 2002). In such cases, the choice of which plate to assign the orthide data to was based on a mixture of literature searches, the similarity of the orthide data from the area in question to the faunas of the possible host plates and lastly the reconstruction software used (PALEOMAP). Fortunately the problematic data usually accounts for only a minor part of the total diversity, which means that the analyses of the data were only slightly affected by their precise placement. In the case of the HCM, orthide data include Baltic endemics, however, also included are genera indicative of a Celtic influence. The data have here been placed within Baltica.

In some cases, the spatial resolution of the data was not good enough to place them on a definite plate, however, as noted above these were not included. Most of the problematic data are related to the greater spatial and temporal uncertainties of Cambrian and Early Ordovician data compared to later Ordovician and Silurian data.

Ireland posed another problem due to the exotic or suspect nature of some of the terranes of the island. The Central Terrane with the two smaller eastern Grangegeeth and Bellewstown terranes encompass most of the uncertainty. The northern terranes of Ireland and the southern Leinster Terrane (Fortey et al. 2000) are, however, firmly established as belonging to Laurentia and Avalonia, respectively, during the Ordovician-Silurian. Data from the northern Irish terranes and the southern Leinster Terrane were included in the analysis. Data from the Central Terrane, Grangegeeth and Bellewstown terranes were excluded on the grounds that the history of especially the two minor terranes remains uncertain (Fortey et al. 2000).

As a final example of currently debated issues in present palaeoreconstructions, the Precordilleran microcontinent (Fortey and Cocks 2003) of Argentina is somewhat of a rogue phenomenon. The microcontinent includes the fossil faunas of the San Juan Formation and Las Aguaditas Formation, from which much of the faunal data involved in reconstructing the wandering path of the terrane was taken. The Precordilleran terrane may originally have been derived from southeastern Laurentia (Thomas 1991; Astini et al. 1995), more specifically the Ouachita embayment of the southeastern USA (Gerbi 1999; Davis et al. 1997) and is recorded immediately south of the central Iapetus suture during the Late Cambrian-Early Ordovician between Gondwana and Laurentia (Cocks and Torsvik 2002). During the Ordovician-Silurian the microcontinent moved southward and docked to the eastern bend of the South American plate (Fortey and Cocks 2003). This history is tested with the limited orthide data available.