New data on isotopic composition of Jurassic-Early Cretaceous cephalopods

The aim of this paper is to reconstruct the Jurassic-Early Cretaceous climatic conditions using new isotopic data. Paleobotanical data indicate that a cooling occurred gradually just after Late Triassic, and a temperature minimum was reached in the Pliensbachian. This was followed by a climatic optimum in the early Toarcian, cooling in the late Toarcian and a second climatic optimum in the Oxfordian. Published isotopic thermometry data and our new results on isotopic composition of some Jurassic invertebrate shells from the Russian Platform, Poland, Germany and England generally confirm this pattern, and also indicate a third climatic optimum in the Middle Callovian. Middle-Late Mesozoic adult belemnites apparently lived during their spawning phase, in shallow waters similar to extant Nautilus. However, at least juvenile belemnoids, unlike ammonoids, engaged in significant short-term vertical migrations in the water column, reaching colder waters of the upper bathyal zone.