Interpreting biological degradative processes acting on mammalian hair in the living and the dead: which ones are taphonomic?

Abstract

Although the taphonomic (post-mortem) degradation processes relevant to teeth and bones have been well described, those taking place with regards to mammalian hairs have not been characterized to the same extent. This present article describes, in detail, microscopic changes resulting from the actions of biological agents that digest and degrade hairs. The most noteworthy and prevalent agents responsible for the destruction of hair structure are fungi, which use a range of strategies to invade and digest hairs. One of the most important finds to emerge from this study is that taphonomic structures and processes can easily be interpreted by the unwary as 'real', or as class characteristics for a particular animal taxon. Moreover, under certain conditions, 'taphonomic' processes normally associated with the dead are also present on the hairs of the living. This work will improve the reliability of hair examinations in forensic, archaeological and palaeontological applications-in addition, the finding has relevance in the protection of mammalian collections susceptible to infestation. This article also addresses the popular myth that ancient peoples were often red-haired and discusses phenomena responsible for this observation. Insights gained from detailed characterization of taphonomic processes in 95 hairs from a variety of species demonstrate the range and breadth of degradative effects on hair structure and colour. Lastly, the study demonstrates that hairs often tell a story and that there is value of extracting as much morphological data as possible from hairs, prior to destructive sampling for biomolecules.

Keywords: archaeology; forensic investigations; mammalian hairs; microscopy; taphonomy.

Figure 1.

Mammalian hair structure and agents of hair degradation. (a) Pigment granules, (b) medulla and (c) cuticle scales. (Online version in colour.)

Figure 2.

Fungal invasion of hairs. (a) Woolly Mammoth (Jarkov) hair engulfed by hyphae, (b,c) partial removal of cuticle (arrow) and dissolution of cuticle (bracketed) on woolly mammoth (Jarkov) hair, (d) SEM image of a penetrating organ (arrow) embedded in a woolly rhino hair. (e) SEM image of a lateral fungal hypha with an eroding frond (arrow), (f) mycelial mass (arrow) on shaft of woolly mammoth (M10) hair. Scale bars: a = 200 μm, b,c = 100 μm, d = 50 μm, e = 5 μm, f = 20 μm. (Online version in colour.)

Figure 3.

Fungal penetration of hair shafts. (a,b) Thin hyphae invading ancient human scalp hair (Saqqaq) and woolly mammoth (Yukagir) hair (lateral fronds are circled). (c) Lateral hyphae in woolly rhino hair. (d) Extensive mass of lateral hyphae in polar bear flank hair. (e) ‘Needle’ (i) and ‘fissure’ (ii) type damage, to the shaft of woolly mammoth (Yukagir) hair. (f) Surface fungal ‘bloom’ on M26 woolly mammoth hair. Scale bar: a = 50 μm, b = 100 μm, c = 100 μm, d = 200 μm, e = 200 μm, f = 100 μm. (Online version in colour.)

Figure 4.

PMB. (a) ‘Somerton man’ chest hair. (b) Pointed root of scalp hair from a murder victim. (c) Pointed root of Norse Kal male scalp hair. (d) Brush root of woolly mammoth (Jarkov) hair. Scale bar: a = 50 μm, b = 200 μm, c = 100 μm, d = 500 μm. (Online version in colour.)

Figure 5.

Insect larvae damage. (a) Woolly rhino coarse hair, (b) Borum Eshøj ‘young man’ scalp hair. (c) Red deer (Cervus elaphus) dorsal hair. (d) Chest hair from deceased ‘Somerton Man’. Images (a,b,d) show cuspate bite marks caused by larval mandibles. Scale bars: a,b,d = 100 μm, c = 200 μm. (Online version in colour.)