Extended Data Fig. 5: ToF-SIMS and FEG-SEM analysis of untreated and demineralised SSN8DOR11 integument.

a, Negative-ion ToF-SIMS image of untreated epidermis showing the spatial distribution of ions representing phosphate (\({{\rm{PO}}}_{2}^{-}\) and \({{\rm{PO}}}_{3}^{-}\)) in red, eumelanin (C₄H^–, C₆H^–, C₈H^–, C₃N^–, C₃NO^–, C₅N^–, and C₇N^–) in green and silica (\({{\rm{SiO}}}_{2}^{-}\), \({{\rm{SiO}}}_{3}^{-}\) and \({{\rm{SiHO}}}_{3}^{-}\)) in blue. b, Enlargement of the area framed by a white box in a. c, Negative-ion ToF-SIMS spectra derived from the regions demarcated by green lines in b (a remnant melanophore) and a modern Sepia officinalis eumelanin reference sample. Phosphate ions (\({{\rm{PO}}}_{2}^{-}\) and \({{\rm{PO}}}_{3}^{-}\)) are denoted by stars. Data are representative of eight independent measurements from four areas on one sample. d, Negative-ion ToF-SIMS spectrum obtained from the melanosome accumulation inferred to represent the condensed epidermal–dermal interface and superficial dermis, together with a spectrum acquired from modern S. officinalis eumelanin. Note close resemblance between the two spectra, despite reduced intensities from N-containing ions (dashed vertical lines) in the fossil one. e, Positive-ion ToF-SIMS spectrum derived from the same melanosome mat as in d, together with a spectrum from S. officinalis eumelanin. Peaks characteristic of polyaromatic hydrocarbons are indicated by stars. Data are representative of three independent measurements from three areas on one sample. f, FEG-SEM micrograph of the melanosome mass from which the fossil spectra in d and e were acquired, partially overlain by a semi-transparent negative-ion ToF-SIMS image showing N-containing organics (C₃N^–, C₃NO^– and C₅N^–) in green and silica (\({{\rm{SiO}}}_{2}^{-}\), \({{\rm{SiO}}}_{3}^{-}\) and \({{\rm{SiHO}}}_{3}^{-}\)) in red. g, Magnification of the white boxed region in f. Note densely packed melanosomes. Scale bars, 50 µm (f), 10 µm (a, b), 1 µm (g).