Fig. 7: FTIR analysis of Palaeocampa anthrax spines.

a Scan images used to make masks that categorized each scanned area into fossil ‘Matrix’, ‘Spine’ or ‘Tip’ regions, using USNM 38032 d (Neotype MCZ:IP:110208 was also analyzed and incorporated into results). b Mean (thick lines) SNV-normalized spectra for each mask category, with 95% percentile ranges shown as confidence bands. c Principal component analysis of SNV pre-processed spectra for the three mask categories across both fossil specimens. d Spectral regions with statistically significant differences between each pair of categories. Upper and lower (Benjamini-Hochberg corrected) boundaries for significance indicated by dashed black horizontal lines with insignificant points grayed-out in between these lines. Differences between tip and spine categories (bottom, dark blue line), have shaded blue bands indicating regions where tip spectra show higher absorbance than spine spectra and have identified local maxima in the spectra corresponding to likely spectral peaks (black annotated numbers). e Spaghetti plot of variation across individual scanning runs between different categories. As in Supplementary Fig. 4, mean values for standard-normal-variate pre-processed, Savitzky-Golay smoothed spectra are presented for each category in each individual scanning run, overlaid to highlight systematic differences between categories in different spectral regions. Dotted lines with wavenumbers at the top denote peaks in the global average of the tip spectra, as identified by the ‘findpeaks’ function of the pracma package⁹⁸, using minimum up and down values of 3 with minimum distance between peaks of 20.