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± Values are one s.e., or in the case of water isotope values, the propagated s.e.
*Samples were considered to be of uncertain preservation if not enough information from multiple sources was available to make an informed assessment or if different types of analyses were not conclusive. See Supplementary Note 3 for full description of steps taken to assess preservation, and Supplementary Table 4 for justification for classification of individual specimens.
†Represents the number of distinct extractions of CO2 from a sample that were separately purified and analysed. See Supplementary Table 3 for additional data for samples.
Stable isotope values of the carbonate mineral.
§Values given on the ‘absolute reference frame’20.
¶Calculated using a compilation of published biogenic calibration (Equation (3), Supplementary Note 2) data collected in the Caltech laboratories and synthesized by Eagle et al.26. See Supplementary Note 2 text for more information on how this calibration was derived.
#δ18O of mineral formation waters calculated using the equation of Kim and O’Neil38, and using the Δ47 (Biogenic) temperature). All eggshells are calcite. Error represents propagated one s.e.