Palaeontological collections made on the 1985 Geotraverse are used to date the associated strata and provide information about palaeoenvironments. A biostratigraphical and palaeoenvironmental framework for the Tibetan plateau is constructed. The crucial stratigraphical and palaeontological evidence for dating volcanic sequences, flysch basins, open oceanic sediments, latest marine sediments and terrestrial red beds in each terrane is reviewed. A quantitative palaeobiogeographical analysis from the Carboniferous to early Triassic is presented for the Tibetan fauna and flora, to establish the biotic relationships between the various terranes. This is based largely on coral, brachiopod and fusulinid distributional data, but other groups have also been analysed, including the Permian terrestrial flora. This analysis demonstrates a clear diversity gradient from equatorial or sub-equatorial biotas in the north to temperate biotas in the south during the late Palaeozoic. No suture line consistently marks the position of a faunal/floral break during the late Palaeozoic and there appears to have been no physical barrier (such as a large ocean) to biotic dispersal between Tibetan terranes at this time. Climate is seen as the most likely factor dominating biotic distribution in this region and the early Permian glaciation had a profound effect on marine faunal distributions in Tibet. 1. The late Palaeozoic biota ranged from equatorial or sub-equatorial in the north to temperate(southern) in the south. 2. Climatic fluctuation on a global scale controlled the distribution of the biota of this region during the late Palaeozoic and no suture zone can be identified as a consistent boundary between `Gondwanan' (i.e. temperate southern) and `Cathaysian' (i.e. equatorial) biotas. 3. It is therefore suggested that either the whole region formed one continuous shelf region at this time, or that, under an island terrane model, the terranes formed `island' platforms spread out across the region more or less uniformly. There is no evidence for any consistent dichotomy at one particular suture zone, nor for any one suture zone marking a significant barrier to faunal dispersal. 4. There is no evidence for any Upper Palaeozoic continental rise or oceanic sediments on the Tibetal plateau. The earliest evidence is of early Triassic turbidites and late Triassic radiolarian cherts. This is contrary to the expectations of an island terrane model. 5. The breakup of this region may date from the permian.