The development of a palaeothermometer for ancient oceans has been a prime goal of stable isotope geochemistry since its inception in the middle of the last century. Following the calibration of the calcite oxygen isotope palaeothermometer by Epstein et al. (1953), and expanding on the seminal papers by Cesare Emiliani, the technique blossomed into a widely applied tool of palaeoceanography. These studies resulted in major advances in our understanding of Quaternary, and to some extent Tertiary oceans, but for older time periods the effort is mired by controversy and is at a standstill. In part this is due to the dearth of well-characterized carrier phases for the temperature signal, such as foraminifera shells, in the pre-Tertiary strata, but an intractable disagreement among practitioners as to the oxygen isotopic composition of ancient seawater is probably a more important stumbling block.