Polar heat wave. Arctic (left) and Southern Ocean (right) temperatures over the past 112 million years based on leaf physiognomy analyses of Arctic plant assemblages and oxygen isotope analysis of planktic and benthic foraminifera from Southern Ocean deep- sea sites. Isotopic paleotemperatures were calculated with the paleotemperatures equation of Anderson and Arthur (12), assuming a mean oceanic d¹⁸O value of -1.2 per mil. Standard mean ocean water for an ice-free Earth (13). Surface-water paleotemperature estimates incorporate the latitudinal salinity correction of Zachos et al. (13). Lower and upper (? = uncertain) paleotemperature implications of champsosaur discovery by Tarduno et al. (1) are also shown.