Figure 2. Representative SR-FTIR spectra.

Baseline-corrected and normalized characteristic infrared band assignment for preserved collagen within the central vascular canals shown in red, and the peaks were assigned for methyl group (_sCH₃ and _as CH₃) and methylene (_sCH₂ and _as CH₂) in the spectral range of 3,000–2,800 cm⁻¹ as shown in the blue inset, collagen type I from extant calf skin dispersed in 0.1% acetic acid solution in green, preserved protein remains in flat fragments found in and near the central canals of the fossil bone in blue, bone matrix in brown, extant bacteria biofilm in black and epoxy resin in pink. It is evident that the spectra of preserved collagen and extant collagen type I are closely matched. The extant bacterial biofilm showed significant differences from fossil or extant collagen in the range of 3,100–3,600 cm⁻¹ region (_sOH).