Figure 2: Pliensbachian to Bajocian oxygen-isotope record plotted against subzone numbers.

Data obtained from pristine and biostratigraphically well-constrained marine calcite fossils from selected European basins (Methods section, Supplementary Data 1, Supplementary Table 1). Shading behind the oxygen-isotope data highlight warm (red) and cool (blue) palaeotemperatures. Plot symbol shape indicates macrofossil type and colour indicates locality. The plot highlights the abrupt and large magnitude shift towards cold seawater temperatures in the earliest Middle Jurassic which, in Hebrides Basin, represents at least 10 °C (Fig. 3). The Late Pliensbachian Cold Event and the Toarcian Oceanic Anoxic (hot) Event are also represented. Superimposed higher frequency climate changes are present during the complete time span for all localities. Data ranges for specific times reflect expected (annual) temperature changes^16,27 and habitat effects²⁸.