Advances in identifying archaeological traces of horn and other keratinous hard tissues

Abstract

Despite being widely utilized in the production of cultural objects, keratinous hard tissues, such as horn, baleen, and tortoiseshell, rarely survive in archaeological contexts unless factors combine to inhibit biodeterioration. Even when these materials do survive, working, use, and diagenetic changes combine to make identification difficult. This paper reviews the chemistry and deterioration of keratin and past approaches to the identification of keratinous archaeological remains. It describes the formation of horn, hoof, baleen, and tortoiseshell and demonstrates how identification can be achieved by combining visual observation under low-power magnification with an understanding of the structure and characteristic deterioration of these materials. It also demonstrates how peptide mass fingerprinting of the keratin can be used to identify keratinous tissues, often to species, even when recognizable structural information has not survived.

Molecular markers in keratins from Mysticeti whales for species identification of baleen in museum and archaeological collections

“…Elsewhere, there is little known about traditions of baleen use, even though whale remains and artefacts made of whale bones have been found in many archaeological sites (for instance in Northern Europe [ 34 – 37 ], South America [ 38 ] and New Zealand [ 39 , 40 ]). In the United Kingdom for example, only two archaeological finds of baleen are known [ 41 ]. This is likely due to the poorer preservation of keratinous tissues in warm and temperate climates compared to bone.…”

“…The inorganic component of baleen is much lower than in bone; in sei whales, for example, the hydroxyapatite content has been estimated at only 4.5% [ 42 ]. Without the protective mineral component, baleen, like other keratinous tissues, would be susceptible to biodegradation [ 41 ].…”

“…Due to its tough and flexible properties, the material was used for a wide range of objects and acquired a high commercial value. As early as the 13 th c. A.D., baleen was used in Europe in the construction of armor and tourney equipment [ 41 ]. During the 18 th and 19 th c. A.D., when exploitation of baleen was at its maximum, the plastic material was made into sheets, strips or rods and used in items of clothing (stays, corsets and hoop skirts) [ 43 ], and in the production of objects such as umbrella stays, eyeglass frames, combs, boxes, etc.…”

“…During the 18 th and 19 th c. A.D., when exploitation of baleen was at its maximum, the plastic material was made into sheets, strips or rods and used in items of clothing (stays, corsets and hoop skirts) [ 43 ], and in the production of objects such as umbrella stays, eyeglass frames, combs, boxes, etc. [ 31 , 41 , 43 ].…”

Experimental Taphonomy of Keratin: A Structural Analysis of Early Taphonomic Changes

“…Keratins such as feathers, pelts, and hair, spun and weaved into textiles, are rare in archaeological sites (e.g., Hargrave 1960;Messinger 1965;Brom 1986;Reinhard and Bryant 1992;Rogers et al 2002;Dove et al 2005). Although peptides can persist in some circumstances due to anaerobic, acidic conditions and occasionally through the association with toxic metals (e.g., copper), iron presence results in only a corrosion cast and/or pseudomorphs of the keratin (Solazzo et al 2014;O'Connor et al 2015). Millennia of diagenetic forces can degrade keratin, which is robust relative to other proteins due to extensive disulphide cross-linking by the amino acid, cysteine.…”