In their paper, now published in Scientific Reports, the team analyzed a sample from a 66-million-year-old Tyrannosaurus rex tibia to provide evidence that vertebrate blood vessels – collagen and elastin structures that don’t fossilize like mineral-based bone – may persist across geologic time through two natural, protein-fusing “cross-linking” processes called Fenton chemistry and glycation.
First, the scientists used imaging, diffraction, spectroscopy, and immunohistochemistry to establish that structures present in the sample are indeed the animal’s original collagen-based tissue. Then, Berkeley Lab co-authors Hoi-Ying Holman and Sirine Fakra respectively performed synchrotron radiation-based Fourier-transform infrared spectromicroscopy (SR-FTIR) to examine how the cross-linked collagen molecules were arranged, and X-ray fluorescence (XRF) mapping to analyze the distribution and types of metal present in T. rex vessels.
“SR-FTIR takes images and spectra of the same sample, and so you can reveal the distribution of protein-folding patterns, which helps to identify the possible cross-linking mechanisms,” said Holman, a senior scientist in the Molecular Biophysics & Integrated Bioimaging Division.
Fenton chemistry and glycation are both non-enzymatic reactions – meaning they can occur in deceased organisms – that are driven by the iron present in the body. “The XRF microprobe revealed the presence of finely crystalline goethite, a very stable iron oxyhydroxide mineral, on the vessels that likely contributed to the preservation of organic molecules,” said Fakra, an ALS research scientist.
The authors believe that the cross-linking reactions they found evidence of, combined with the protection offered from being surrounded by dense mineralized bone, can explain how original soft tissues persist.