RATIONALE: Non-enzymatic deamidation accumulates in aging tissues in vivo and 
has been proposed to be potentially useful as a molecular clock. The process 
continues post mortem, and here we explore the increase in levels of deamidation 
in archaeological collagen, as measured during Zooarchaeology by Mass 
Spectrometry (ZooMS) analysis.
METHODS: With the high sensitivity of current generation mass spectrometers, 
ZooMS provides a non-destructive and highly cost-effective method to 
characterise collagen peptides. Deamidation can be detected by mass spectrometry 
as a +0.984 Da mass shift; therefore, aside from its original purpose, peptide 
mass-fingerprinting for bone identification, ZooMS concurrently yields a 
'thermal indicator' of the samples.
RESULTS: By analysis of conventional ZooMS spectra, we determined the 
deamidation rate for glutamine residues in 911 bone collagen samples from 50 
sites, with ages varying from medieval to Palaeolithic. The degree of 
deamidation was compared to diagenetic parameters and nearby sequence 
properties.
CONCLUSIONS: The extent of deamidation was found to be influenced more by burial 
conditions and thermal age than, for example, chronological age, the extent of 
bioerosion or crystallinity. The method lends itself mostly to screening 
heterogenic deposits of bone to identify outliers.