Preservation of corneous beta proteins in Mesozoic feathers

S-XANES data. Small samples (≥3 mm2) of untreated and experimentally degraded feathers in addition to fossil material and samples of host sediment were placed on low-sulfur mylar tape and analyzed at the Stanford Synchrotron Radiation Lightsource (SSRL) using synchrotron X-ray absorption near-edge spectroscopy (XANES) at beam line 6-2. S-XANES data were collected in fluorescence mode using a single element Vortex silicon drift detector set at an angle of ~90° to the incident beam to minimize the scatter signal. The incident x-ray energy was selected using a Si(111) monochromator, which was calibrated using a Na2S2O3 standard with the thiol pre-edge peak defined as 2472.02 eV. S-XANES standards for selected S-bearing compounds, representing different S species, were prepared by mixing commercially available analytical standards (Sigma Aldrich; ≥98% pure) with BN to obtain a S concentration of ca. 5 wt% in each standard. Data alignment, averaging, background subtraction and normalisation were performed using Athena v. 0.9.26.

FTIR data. Fossil data were collected in the 4000–600 cm-1 range using a PerkinElmer Frontier FTIR spectrometer fitted with a Spotlight 400 microscope. Each spectrum was collected as an average of 8–36 scans. Spectra for untreated and matured feathers were collected in the 4000–500 cm-1 range using a universal diamond ATR accessory on the Frontier spectrometer. Each spectrum was collected as an average of 10 scans. Each spectrum was baseline-corrected using SpectraGryph v. 1.2.7 using the parameters adaptive correction, 15% coarseness and no offset. In addition, interactive baseline correction was performed on data in the region 898–450 cm-1 using Spectrum IR v. 10.6.1 (PerkinElmer, USA). This ensured a consistent baseline across the entire scan range to facilitate spectral comparison. Each spectrum was standardized to remove sample thickness effects.