Quality control for modern bone collagen stable carbon and nitrogen isotope measurements

(1) Isotopic analyses of collagen, the main protein preserved in sub fossil bone and tooth, has long provided a powerful tool for the reconstruction of ancient diets and environments. Although isotopic studies of contemporary ecosystems have typically focused on more accessible tissues (e.g., muscle, hair), there is growing interest in the potential for analyses of collagen because it is often available in hard tissue archives (e.g., scales, skin, bone, tooth), allowing for enhanced long-term retrospective studies. The quality of measurements of the stable carbon and nitrogen isotopic compositions of ancient samples are subject to robust and well-established criteria for detection of contaminants and digenesis. Among these quality control (QC) criteria, the most widely utilized is the atomic C:N ratio (C:NAtomic), which for ancient samples has an acceptable range between  2.9 and 3.6. While this QC criterion was developed for ancient materials, it has increasingly being applied to colla..., Establishing an observed range for vertebrate collagen C:NAtomic
To establish the natural range of C:NAtomic for vertebrate collagen we surveyed a wide body of data from the food chemistry literature. Amino acid compositions are from both acid and pepsin solubilized collagens. Comparing C:NAtomic ratios from studies that performed both methods on collagen from 13 species, Szpak (2011) found that amino acid compositions measured using acid and pepsin solubilized collagen were nearly identical with no statistically significant differences. Data from both types of collagen extraction techniques should therefore produce amino acid compositions that are comparable for our purposes. Because fish collagens are adapted to environmental conditions (Eastoe 1957; Gustavson 1955), we further grouped fish based on habitat preferences using classifications provided on FishBase (Froese and Pauly 2000) as follows: warm water (tropical, subtropical) and cold water (temperate, polar, boreal, and deep-wa..., The following documents are included:
Table S1. Amino acid compositions for collagen and non-collagenous proteins collected from published literature. All data are presented as residues/1000. Materials code: 1= bone, 2 = scale, 3=skin. Temperature code: 1 = cold water, 2 = warm water.
Table S2. Statistical results: Shapiro Wilks tests for C:NAtomic for different taxonomic groups.
Table S3. Results for Spearman’s ρ tests for collagen δ13C grouped by ascending C:NAtomic
Table S4. Extent to which shifts C:NAtomic (resulting from lipid contamination) affect δ13C. Comparison made with data generated by recent studies (Guiry, et al. 2016; Szpak and Guiry In Prep) on the effects of collagen extractions methods on the elemental and isotopic compositions of 122 bones from 85 fish, mammal, and bird specimens from diverse taxa and environments. Four to five extraction procedures were applied to subsamples from each bone. Within each group of four to five samples per bone, the δ13C of the sample wi...