The discovery of petrous bone as an excellent repository for ancient biomolecules has been a turning point in biomolecular archaeology, especially in the recovery of ancient genomes. Although the information extracted by the biochemical analyses of petrous bone can be valuable, the processes are destructive, expensive and time consuming, while excessive and uncontrolled sampling could result in loss of this valuable resource for future research.
This study reports on the histological (optical microscopy), physical (FTIR-ATR), elemental (CN), biomechanical (nanoindentation) and biochemical (collagen and DNA analysis) preservation of 272 bones spanning from c. 10.000 BC to c. 1850 AD, including 108 petrous bones. Through the combined application of a number of diagenetic parameters (general histological index; infrared splitting factor; carbonate/phosphate ratio; amide/phosphate ratio; col wt. %; % C, % N and C/N of whole bone and collagen; hardness, elastic modulus, % endogenous DNA), new insights into petrous bone micromorphological and diagenetic characteristics, inter-site, intra-site, intra-individual and intra-bone diagenetic variability, and new evidence to enhance successful screening of archaeological bone prior to aDNA and collagen analysis is presented.
Specifically, the petrous bone microstructure consists of highly osteocytic woven and lamellar-like tissues, and osteons occur in at least two directions (transverse and longitudinal). Despite its stunning micromorphological characteristics, the biomechanical properties and diagenetic characteristics of petrous bone do not differ significantly from those of long bones. Inter-site and intra-site diagenetic variability is mostly affected by the site hydrology, while different types of burials can influence the microenvironment conditions and leave distinctive marks on bone histology. No intra-individual patterns, which could also favour the gut origin of microbial attack in bone, or intra-bone variability are observed in any of the diagenetic parameters. Screening archaeological bone for collagen preservation can be enhanced using the % C of whole bone which is equally strong as % N of whole bone collagen predictor, while the IRSF (< 3.7) and C/P (> 0.15) indices can distinguish bones containing >1 % endogenous DNA with a success rate of c. 85 % as bioapatite preservation is associated with loss of DNA.
