Seaweed-eating sheep and the adaptation of husbandry in Neolithic Orkney: new insights from Skara Brae

Abstract

Abstract

Identifying seaweed consumption by sheep using isotope analysis of their bones and teeth: Modern reference δ13C and δ15N values and their archaeological implications

“…However, the only two adult sheep from the same site (albeit likely different individuals to those analysed for δ 13 Cenamel) that were analysed for δ 13 Ccollagen did not show evidence of seaweed consumption (−19.8 ‰ and −20.1 ‰; Schulting and Richards, 2009). A similar discrepancy between enamel and bone δ 13 C results at site level was found at Skara Brae, where sheep collagen δ 13 C results were comparatively low (−21.1 ‰ to −20.3 ‰; Jones and Mulville, 2016), yet sequential tooth enamel δ 13 C analyses indicated substantial seasonal seaweed consumption (Balasse et al, 2019). Similarly, at the Knap of Howar, recent reinterpretation of sequential δ 13 Cenamel results indicates seasonal seaweed consumption in small amounts by some sheep (Balasse et al, 2019(Balasse et al, , 2006, while δ 13 Ccollagen results (potentially performed on different sheep; ranging from −20.7 ‰ to −18.8 ‰) have been interpreted as not being indicative of seaweed consumption (Bronk Ramsey et al, 2002;Schulting and Richards, 2009).…”

“…A similar discrepancy between enamel and bone δ 13 C results at site level was found at Skara Brae, where sheep collagen δ 13 C results were comparatively low (−21.1 ‰ to −20.3 ‰; Jones and Mulville, 2016), yet sequential tooth enamel δ 13 C analyses indicated substantial seasonal seaweed consumption (Balasse et al, 2019). Similarly, at the Knap of Howar, recent reinterpretation of sequential δ 13 Cenamel results indicates seasonal seaweed consumption in small amounts by some sheep (Balasse et al, 2019(Balasse et al, , 2006, while δ 13 Ccollagen results (potentially performed on different sheep; ranging from −20.7 ‰ to −18.8 ‰) have been interpreted as not being indicative of seaweed consumption (Bronk Ramsey et al, 2002;Schulting and Richards, 2009). In contrast, distinctly marineinfluenced δ 13 Ccollagen values (−18.6 ‰ to around -13 ‰) have been found in five young lambs from Holm of Papa Westray North Cairn and Neolithic Quanterness, Orkney (Bronk Ramsey et al, 2009Schulting et al, 2004Schulting et al, , 2017Schulting and Richards, 2009), whereas δ 13 Ccollagen of older sheep from the same sites did not clearly indicate a marine influence (Schulting and Richards, 2009).…”

“…Particularly in the North-West of Europe, seaweed is already known to have been consumed by, and fed to domesticated animals including sheep, cattle and pigs both today and historically (Bell, 1981;Fenton, 1997;Martin, 1716;Towsey, 2002). Additionally, stable carbon isotope ratio measurements on sheep's teeth and bones from the Orkney Islands, Scotland, have provided the first archaeological evidence of seaweed consumption by sheep, with earliest evidence from the Neolithic onward (around 3000 BC; Balasse et al, 2019Balasse et al, , 2005Dockrill et al, 1994). However, references to seaweed consumption by domesticated animals outside of Orkney are rare in the archaeological literature.…”

“…However, references to seaweed consumption by domesticated animals outside of Orkney are rare in the archaeological literature. This may be due to a lack of awareness of seaweed as a potential food source (Bell, 1981), or its (mistaken) dismissal as not applicable outside of Orkney, but crucially could also be caused by unfounded expectations of how seaweed consumption would be reflected in stable isotope ratios in consumer skeletal tissues (Balasse et al, 2019). Seaweed species most commonly consumed by livestock generally have δ 13 C values between −21 ‰ and −13 ‰ (Hansen et al, 2003a;Raven et al, 2002), while terrestrial C3 plant material have lower δ 13 C values (generally between −32 ‰ and −23 ‰, Kohn, 2010) and C4 plant material higher δ 13 C values (around −10 to −16 ‰, Basu et al, 2015;O'Leary, 1988).…”

Specialized cattle farming in the Neolithic Rhine-Meuse Delta: Results from zooarchaeological and stable isotope (δ18O, δ13C, δ15N) analyses

“…Values below –22.5‰ in collagen can be considered as the key value for grazing in open areas and an indication of resources from a closed-canopy environment [ 68 ]. Contribution of resources from marine/estuarine environments leads to elevated δ 13 C and δ 15 N values in bone collagen, whereas freshwater/riverine components will be reflected in low δ 13 C values compared to the terrestrial ecosystems [ 69 , 70 ]. Saltmarsh grazing is proved to elevate the δ 15 N values significantly (approximately 3‰) compared to other terrestrial resources as a result of salinity and sea-spray effect [ 71 ].…”