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 inte rval of each epoch which can be interpreted climatically as ranging th rough the dry subtropical to the warm and cool temperate biomes. Flora s 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 high est diversity, centered at about 40-degrees palaeolatitude, occurs in the intermediate warm temperate zone which may contain all of the abov e floral elements in association with numerous fern and cycad genera. The transitions between these biomes remained at relatively constant l atitudes, from the late Triassic to the early Cretaceous, suggesting c limate stasis over a long interval. Climate changes, perceived locally , appear to be the result of continental motion rather than true globa l change. During the early and middle Triassic, however, the biomes ar e less distinct, with floras interpreted as warm temperate extending t o latitudes of up to 70-degrees north.