'Palaeoshellomics’ reveals the use of freshwater mother-of-pearl in prehistory

Abstract

The extensive use of mollusc shell as a versatile raw material is testament to its importance in prehistoric times. The consistent choice of certain species for different purposes, including the making of ornaments, is a direct representation of how humans viewed and exploited their environment. The necessary taxonomic information, however, is often impossible to obtain from objects that are small, heavily worked or degraded. Here we propose a novel biogeochemical approach to track the biological origin of prehistoric mollusc shell. We conducted an in-depth study of archaeological ornaments using microstructural, geochemical and biomolecular analyses, including ‘palaeoshellomics’, the first application of palaeoproteomics to mollusc shells (and indeed to any invertebrate calcified tissue). We reveal the consistent use of locally-sourced freshwater mother-of-pearl for the standardized manufacture of ‘double-buttons’. This craft is found throughout Europe between 4200–3800 BCE, highlighting the ornament-makers’ profound knowledge of the biogeosphere and the existence of cross-cultural traditions.

The shell matrix of the european thorny oyster, Spondylus gaederopus: microstructural and molecular characterization

“…The finding that Spondylus matrices are rather organic-poor is consistent with the data obtained on other cross-lamellar (Agbaje et al, 2019;Demarchi et al, 2015;Marie et al, 2013a;Osuna-Mascaró et al, 2014) and foliated (Pierini et al, 2016) shells; this contrasts to what is observed in organic-rich nacreous and prismatic microstructures (Marie et al, 2009b;Marin et al, 2013;Sakalauskaite et al, 2019). As spondylids represent a bivalve family that emerged rather recently, in the Middle Jurassic (Waller, 2006), our observations corroborate the pioneering idea of Palmer that, in molluscs, the "cost" for making a shell is mostly driven by the "cost" to synthesize the organic matrix (Palmer, 1992); we can argue that evolution was directed to strike a balance between the mechanical properties of a biomineral and the actual "cost" required to produce it.…”

“…1) Shell matrix proteins are frequently characterized by the presence of repeated low complexity domains (LCDs or RLCDs, frequently found as long poly-Ala/Asp/Ser/Gly blocks (Kocot et al, 2016;Marie et al, 2017;Sakalauskaite et al, 2019), and post translational modifications such as phosphorylation (Du et al, 2018) and glycosylation (Boskey and Villarreal-Ramirez, 2016;Mann and Edsinger, 2014), making the protein sequences difficult to cleave using standard proteases and thus reducing the chance of identification.…”

“…Most of these studies focused on mother-of-pearl shells (Marie et al, 2017(Marie et al, , 2013aRamos-Silva et al, 2012;Yarra et al, 2016), shedding light on some characteristics of shell proteins (Arivalagan et al, 2017;Sleight et al, 2016). One interesting feature, is the widespread occurrence of low complexity domains/ repetitive low complexity domains (LCDs/RLCDs) (Kocot et al, 2016;Marin et al, 2016Marin et al, , 2014) -these were identified in proteins associated with nacre (Jackson et al, 2010;McDougall et al, 2013;Sakalauskaite et al, 2019) but were also found in shell proteomes associated with other microstructures (Marie et al, 2013a), suggesting that these domains likely play a role in mineral binding and in providing flexibility (Sarashina and Endo, 2006). However, most importantly, 'shellomics' has also exposed the diversity of the SMP repertoires between shells that have similar microstructures or species that are phylogenetically close (Jackson et al, 2010;Marie et al, 2009aMarie et al, , 2009b.…”

“…In this context, our study has a dual goal: 1) characterizing the shell microstructure of Spondylus gaederopus and the molecular properties of the associated organic matrix, followed by an in-depth proteomics study; 2) establishing a biomolecular dataset for the Spondylus shell matrix, which will constitute a reference in future studies to identify the biological origin of fragments of prehistoric shell ornaments, where morphological identification is unattainable (Demarchi et al, 2014;Sakalauskaite et al, 2019), taking into account the diagenetic processes.…”

Eumelanin and pheomelanin pigmentation in mollusc shells may be less common than expected: insights from mass spectrometry

“…The colouration and patterning of the molluscan shell and associated biominerals (e.g. pearls) have fascinated human cultures since prehistoric times [5–10]. The pigmentation of these structures holds not only aesthetic beauty, but can also dictate their commercial value [11–13].…”