Palaeobiogeography of early planktonic foraminifera

Abstract

Abstract Over the last 50 years, our knowledge of early planktonic foraminifera has changed markedly. In 1958 Grigelis described “Globigerina oxfordiana” from the Upper Jurassic of Lithuania and this has, subsequently, become identified as one of the most geographically widespread of Jurassic planktonic taxa. There is a danger in that many authors identify any planktonic foraminiferid from the Jurassic as this taxon, rather than consider the alternative species described in the literature. In the period from 1967 to 1973, however, Dr W. Fuchs (Austria) identified a number of new taxa from the Triassic and Jurassic of Austria and the Jurassic of Poland and claimed that the history of planktonic foraminifera began in the Triassic. Following a long re-investigation of all his material in the Geologische Bundesanstalt in Vienna by the authors it appears that one of his new genera, Praegubkinella, was probably the ancestor of Conoglobigerina in the Toarcian (Early Jurassic). The first conoglobigerinids have been described from Toarcian – Aalenian – Bajocian strata in Central and Eastern Europe (including parts of the Former Soviet Union). The palaeobiogeography of Conoglobigerina and other related genera such as Globuligerina, Haeuslerina and Compactogerina are discussed and the problems yet to be resolved (e.g., records of “planktonic” taxa in the Triassic/Jurassic offshore N.W. Australia) are documented. The distribution (and evolution) of the Jurassic and Early Cretaceous planktonic foraminifera appear to be related to sea level highstands and continental fragmentation, especially in the earliest Cretaceous.