Establishing Decay Rates for Bone Collagen in Different Organisms Using Fourier Transformed Infrared (FTIR) Spectroscopy

Collagen is the most abundant protein in vertebrates. Due to its compact triple helical structure, collagen is exceptionally stable; however, it is still subject to spontaneous hydrolytic reactions which break peptide bonds and ultimately lead to its degradation. In 1997, Mary Schweitzer published some of the first evidence of extant biological tissue in dinosaur bones (Schweitzer 1997). Since then, numerous studies have reported a range of surviving structures in dinosaur bones including blood vessels, osteocytes, and endogenous proteins such as collagen (Boatman 2019). Based on the assigned ages of these fossils (>65 Ma), the presence of endogenous biomolecules such as collagen was surprising because of theoretical limits on the persistence of proteins through deep time. The presence of such proteins has led to speculation about the processes that regulate collagen decay, yet few studies have measured the decay rate of bone collagen. The presence and relative abundance of bone collagen can be tested by using Fourier-transformed infrared (FTIR) spectroscopy to measure spectral absorbance patterns of powderized bone samples (Scaggion 2024; Thomas 2023). Our lab has pioneered the use of FTIR to examine changes in the amount of bone collagen in artificially degraded samples. By subjecting modern bone fragments to heat, we accelerate the decay rate of bone collagen and can construct decay curves to calculate the rate of collagen degradation at paleontologically relevant temperatures. To better understand the taphonomic differences between animal taxa, we are measuring bone collagen decay in mammalian, avian, and reptilian bones. By using this artificial degradation protocol, we have calculated the half-life for bone collagen at 25 oC in a neutral aqueous environment to be 1086 yrs and 296 yrs for mammalian and avian bone, respectively. Although it is a stable protein, under these conditions bone collagen levels will drop below 1% in less than 10,000 years. Even at lower temperatures (i.e. 10 oC), the life expectancy of collagen falls far short of the conventional ages assigned to the dinosaur bones in which it is found. While several factors impact collagen decay besides thermal properties, such as the presence of microorganisms which would accelerate decay and the presence of crosslinking which may prolong decay, our data establish a baseline with which to compare future experiments testing proposed models of preservation. If reasonable natural preservation methods cannot be identified which significantly extend the decay rate of collagen, then the assigned ages of these fossils should be re-examined. References: Schweitzer, Mary Higby, Craig Johnson, Thomas G. Zocco, John R. Horner, and Jean R. Starkey. 1997. “Preservation of Biomolecules in Cancellous Bone of Tyrannosaurus Rex.” Journal of Vertebrate Paleontology 17 (2): 349–59. https://doi.org/10.1080/02724634.1997.10010979. Boatman, Elizabeth M., Mark B. Goodwin, Hoi-Ying N. Holman, Sirine Fakra, Wenxia Zheng, Ronald Gronsky, and Mary H. Schweitzer. 2019. “Mechanisms of Soft Tissue and Protein Preservation in Tyrannosaurus Rex.” Scientific Reports 9 (1): 15678. https://doi.org/10.1038/s41598-019-51680-1. Scaggion, Cinzia, Maurizio Marinato, Gregorio Dal Sasso, Luca Nodari, Tina Saupe, Serena Aneli, Luca Pagani, Christiana L. Scheib, Manuel Rigo, and Gilberto Artioli. 2024. “A Fresh Perspective on Infrared Spectroscopy as a Prescreening Method for Molecular and Stable Isotopes Analyses on Ancient Human Bones.” Scientific Reports 14 (1): 1028. https://doi.org/10.1038/s41598-024-51518-5. Thomas, Brian, Kevin Anderson, Imesha De Silva, Guido Verbeck, and Stephen Taylor. 2023. “Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopy Sensitivity to the Thermal Decay of Bone Collagen.” Applied Spectroscopy 77 (1): 53–61. https://doi.org/10.1177/00037028221135634.