Taxonomy, location of origin and health status of proboscideans from Western Canada investigated using stable isotope analysis

Abstract

We investigated the application of stable isotope analysis of proboscidean remains (collagen in bone/dentin/cementum and structural carbonate in enamel bioapatite) for genus-level identification of isolated specimens, assessment of geographic origins, and testing for nutritional stress. Mammoths (Mammuthus sp.) tended to have higher δ 15 N col and lower δ 13 C col than mastodons (Mammut americanum), but differences were not significant in every location.Determining the genus of isolated specimens may be possible for locations and time periods with good isotopic baselines, but environmental changes can confound interpretations. For example, an Alberta proboscidean with a δ 15 N col of +1.4‰ (characteristic of mastodons) ultimately proved to be a mammoth. Its surprisingly low nitrogen isotope composition is attributable to the recently deglaciated environment it inhabited. We provided a baseline for isotopic assessment of geographic origins of isolated proboscideans in Western Canada. Bioapatite δ 13 C sc and δ 18 O sc can be used to distinguish specimens from Alberta, Klondike, Old Crow, Herschel Island, and further south (e.g., Arizona, Great Lakes). Finally, we found that an Alberta mammoth with morphological evidence of nutritional stress experienced a change in diet, environment, or physiology prior to death, but its isotopic compositions did not suggest a link to hypothesized starvation (catabolism of proteins or reliance on lipids).

Nanoscale Imaging and Microanalysis of Ice Age Bone Offers New Perspective on “Subfossils” and Fossilization

“…The type-1 collagen scaffolding of these permafrost bones has undergone limited diagenesis relative to the extensive in-situ polymerization/carbonization observed for soft tissue specimens of earlier geologic strata [18,19,21,22,79]. This agrees with prior studies on bulk permafrost bone extracts that have reported C:N ratios of ~2.9-3.6, implying relatively minimal alteration of the collagen [46][47][48]. Likewise, paleoproteomic sequencing studies of permafrost bone generally report sequence coverage for both peptide chains of type-1 collagen (α1 and α2) >50-60% [40,44,45], roughly comparable to what is reported for extant bone [49,50].…”

“…Both the permafrost and extant specimen C:N ratios were within the range 2.9-3.6, which has historically been accepted as indicating well-preserved collagen. Values for %C and %N (by mass) ranged from 41.0-46.0% and 15.2-17.1%, respectively, which is likewise consistent with the collagenous scaffolding having undergone minimal diagenesis [46][47][48]65]. Measurements of δ 13 C and δ 15 N are also reported; while the obtained values are consistent with prior values obtained from permafrost megafaunal bones, they are more so related to organismal diet/trophic-level and thus are not further discussed [46][47][48].…”

“…Permafrost bones are specifically chosen for this initial investigation because they are well studied regarding gross biochemical preservation. Genomic studies of permafrost bone extracts [40][41][42][43], as well as some proteomic [40,44,45] and isotopic investigations [46][47][48], have reported excellent biochemical preservation. DNA fragments and a diversity of proteins are generally reported [23,40,44].…”

“…Past studies have instead generally used homogenized extracts which preclude localizing chemical signal to biomolecular histology [27]. Finally, carbon:nitrogen (C:N) ratios are reported for the various specimens herein to allow for direct comparison against previous studies of permafrost bone [46][47][48]. The atomic C:N ratio, as well as %C and %N by mass, have historically been commonly used proxies for collagen preservation and are practical for comparing specimens across studies [65].…”