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Information is presented on paleoternperature determinations from the rostra of Jurassic and Lower Cretaceous belen-mites in northern USSR. Mean annual paleotemperatures of the order of 13–25 °C were obtained on the basis of isotopic composition of oxygen (about 100 determinations showing the tendency for higher temperatures between the Bathonian and late Volgian times); and of the order of 10–22 °C, on the basis of Ca/Mg ratio (about 200 determinations). Seasonal fluctuations of paleotemperatures were about 5–7 °C. The conclusion is drawn that the northern reaches of Eurasia were situated approximately within the northern part of the subtropical zone - in the Toarcian, Late Jurassic, and Neocornian; and in the temperate zone - in Middle Jurassic and late Volgian times. --Authors.