Fig. 3

High-resolution Raman maps (3 s exposure time, 3 accumulations) of remains of extracellular matrix extracted from Allosaurus fragilis bone in aqueous hydrochloric acid (pH = 3). The dotted rectangles mark the area mapped, and the different shades of red represent the signal intensity of the protein fossilization product (PFP). The colored spheres framing the compound structures represent a N-heterocycle polymer context, and the red shading labels the functional unit that gives rise to each signal mapped out. The scale bar equals 300 μm. a Dark residue of soft tissue. b Map of N-rich heterocycles (1550–1610 cm⁻¹), which cover most of the sample surface. c Pentosidine (980 cm⁻¹), the AGE marker, which corresponds to the spatial distribution of N-rich heterocycles. d Amide I generated by peptide bonds, which is a less precise match for the N-rich heterocycles (1690 cm⁻¹). e–g The organic functional units representing the selected Raman shifts are shaded (red) below each map