Palaeoclimates and their modelling with special reference to the Mesozoic era - Early Mesozoic phytogeography and climate

Triassic and Jurassic floral lists from Eurasia have been subjected to an ordination study. A latitudinal gradient is revealed for each interval of each epoch which can be interpreted climatically as ranging through the dry subtropical to the w arm and cool temperate biomes. Floras at the dry end of the spectrum may be identified by the dominance of microphyllous conifers and the regional association with evaporites. At the other extreme, the cool temperate floras are recognized by the abundance of deciduous ginkgophytes and broadleaved conifers. The highest diversity, centered at about 40° palaeolatitude, occurs in the intermediate w arm temperate zone which may contain all of the above floral elements in association with numerous fern and cycad genera. The transitions between these biomes remained at relatively constant latitudes, from the late Triassic to the early Cretaceous, suggesting climate stasis over a long interval. Climate changes, perceived locally, appear to be the result of continental motion rather than true global change. During the early and middle Triassic, however, the biomes are less distinct, with floras interpreted as warm temperate extending to latitudes of up to 70° north.