Extended Data Fig. 7: Detailed PCA result of negative ToF–SIMS spectra.
From: Four camera-type eyes in the earliest vertebrates from the Cambrian Period
a, the PCA result of 54 negative secondary ion peaks obtained from the following samples: fresh melanin, artificially matured melanin (aged for 24 h at 200 °C/250 bar and 250 °C/250 bar), fossil melanin, various melanin-negative controls, and specimens of Chengjiang myllokunmingids. b, Comparison of ToF-SIMS full spectra between Haikouichthys eyes (top) with a negative control of the host sediment (bottom) from the Chengjiang biota. c, loadings for principal component analysis (panel a and Fig. 2a), showing the contribution of specific ion fragments to the positioning of specimens along the x-axis (PC1) and y-axis (PC2), respectively. d, the list of details of the numbered samples in a.
