The Irish Caledomde terranes occupied a variety of sites marginal to the cratons of Laurentia, Baltica and Gondwana. Palaeontological data provide age constraints on the timing of sedimentary linkage and the age of overlap sequences. The Northwestern terrane is characterized by the development of Toquima–Table Head faunas in the early Ordovician in contrast to the Celtic faunas of the Bellewstown and Rosslare terranes. During the middle Ordovician the Northwestern terrane and the Scottish equivalent of the Central terrane were occupied by the Scoto–Appalachian fauna. The Leinster terrane was dominated by Anglo-Welsh elements with varying proportions of the Scoto-Appalachian and Baltic faunas across the terrane. In the Iapetus suture zone in the east of Ireland the Grangegeeth terrane is characterized by a predominantly Scoto-Appalachian fauna.