Stable Carbon and Nitrogen Isotope Variability of Bone Collagen to Determine the Number of Isotopically Distinct Specimens

Abstract

Archaeological and palaeontological excavations frequently produce large quantities of highly fragmentary bone. These bones can help to answer questions regarding past environments and human and animal lifeways via a number of analytical techniques but this potential is limited by the inability to distinguish individual animals and generate sufficiently large samples. Using stable carbon and nitrogen isotope values of bone collagen (δ13C, δ15N), we present a metric to identify the number of isotopically distinct specimens (NIDS) from highly fragmented faunal assemblages. We quantified the amount of intra-individual isotopic variation by generating isotopic data from multiple elements from individual animals representing a wide variety of taxa as well as multiple samples from the same skeletal element. The mean intra-individual variation (inter-bone) was 0.52‰ (σ = 0.45) (Euclidean distance between two points in isotopic bivariate space), while the mean intra-bone variation was 0.63‰ (σ = 0.06). Using archaeological data consisting of large numbers of individual taxa from single sites, the mean inter-individual isotopic variation was 1.45‰ (σ = 1.15). We suggest the use of 1.50‰ in bivariate (δ13C, δ15N) space as a metric to distinguish NIDS. Blind tests of modelled archaeological datasets of different size and isotopic variability resulted in a rate of misclassification (two or more elements from the same individual being classified as coming from different individuals) of < 5%.

Four millennia of long-term individual foraging site fidelity in a highly migratory marine predator

“…Mean isotopic compositions from all four types of bone samples (Tarsometatarsi, humeri, coracoids, and wing digits; Supplementary Table 1 ) showed show little variation in δ 13 C (range for means = 0.2‰) and δ 15 N (range for means = 0.8‰). These differences are smaller than expected for typical intra-skeletal isotopic variation 35 indicating that bone type has not influenced isotopic patterns. Samples passing QC criteria produced mean δ 13 C and δ 15 N values of –14.6 ± 0.4‰ and +18.0 ± 0.7‰, respectively (Fig.…”

Combining δ13C and δ15N from bone and dentine in marine mammal palaeoecological research: insights from toothed whales

“…Variation in intraskeletal bone δ 15 N ranged from 0.3 ‰ in walrus and dusky dolphin [41,42] to 1.3 ‰ in South American sea lion ( Otaria flavescens ) (among atlas, humerus and basioccipital [42]). However, other studies could not detect intraskeletal variation when performing similar analysis; e.g., [43] did not detect differences in isotopic composition between cortical and trabecular bone in harp seals ( Pagophilus groenlandicus ).…”

“…Intraskeletal bone variation in δ 13 C and δ 15 N has also been investigated in terrestrial mammals (e.g., in humans [39]; in cow ( Bos taurus ), pig ( Sus domesticus ), long-tailed weasel ( Mustela frenata ), and raccoon ( Procyon lotor) [43]). Using an isotopic distance value estimated from δ 13 C and δ 15 N bivariate plots, Hyland et al 2021 [43] detected an average isotopic distance value of bone sampled within individuals of 0.52 ‰. Our results showed intraskeletal variation between bone and various dentine elements.…”

Changing diets over time: knock-on effects of marine megafauna overexploitation on their competitors in the southwestern Atlantic Ocean

“…In order to avoid pseudoreplication, bones from the neurocranium (fishes) or long limb bones (birds) with the same laterality were used for both ancient and modern specimens. The skeletal elements analyzed for each species varied across archaeological sites, because of uneven occurrence, but intra-individual variability in the stable isotope ratios of skeletal elements of fish and birds is usually much smaller than interindividual variability (Bas and Cardona 2018; Hyland et al 2021).…”