Skeletalisation in Osteoarchaeology

Skeletalisation has been known to take as little as three weeks in hot weather to 18 months. Preservation with some decalcification has been seen with Tollund and Grauballe men. A system of bone dating, to determine ancient from modern has been elaborated (Knight & Lander, 1967; Knight, 1969, 1971; Chaterji & Jeffrey, 1968).

Correlation between chemical and micromorphological structure of bones and degree of composition:
Intensity of decomposition decreases with advancing time, the processes being due to biological, chemical and physical agents. The differences are valuable in determining modern from ancient bones. Bone decomposition passes through five chemico-histological phases (See: Lengyel, Biology of Earlier Human Populations, Budapest).

Phase 1 – Histology. The delicate cellular structure is shown by standard microscopic methods. Osteocytes can be distinguished. Phase 1 – Chemical. Only initial post mortem autolysis. No change in the bone substance.

Phase 2 – Histology. Cellular structure no longer recognisable. Osteocyte lacunae are empty. Collagen can be impregnated with silver. The osteone system is intact. Phase 2 – Chemical. Exogenous influences determine the level of water soluble inorganic and organic substances, which show a considerable decrease. No essential change in collagen amount or resistant proteins. Slight decrease in concentration of calcium, carbonate, phosphate, and magnesium. Bones are rigid.

Examples from the 10th century bones from Tiszanan and Heves in Hungary illustrate this phase (Lengyel).

Phase 3 – Histology. Cellular structure has disappeared. Collagen is fragmented and unevenly impregnated with silver. The osteones are intact. Phase 3 – Chemical. Collagen and resistant proteins have decreased. Fall in level of osseous origin inorganics, which progresses hand in hand with inorganic invasion from soil. The bone substance begins friability or remains at Phase 2. Progression of friability depends on cause of death and the Phase 1 factors.

Examples from Keszthely-Dobogo graveyard (Veszprem in Hungary) from the 4th and 5th century. (Lengyel).

Phase 4 – Histology. Collagen no longer impregnable with silver. Ground substance is saturated with inorganic salts. Osteones are intact. Phase 4 – Chemical. Collagen concentration is low. The amount ofinorganics coming from the soil is so large that it is no longer possible to distinguish endogenous/exogenous calcium, phosphorus, and carbonate salts. Bones are strongly friable, or in initial stages of petrification.

Examples from graveyard at Alsonmedi (Pest, Hungary), dated from the Copper Age.
Phase 5 – Histology. Nothing but the boundaries of the osteones and Haversian canals remain. Phase 5 – Chemical. There are only traces of inorganic matter. Chemical reactions of an exogenous/endogenous nature have reached an equilibrium. This is the phase of complete mineralisation. The petrified layer is formed on the bone surface and thickens gradually. The bone substance is friable like chalk, or cracking and fragile like stone.

Examples were Solo IX and Homo (Pithecanthropus) erectus III.

Determination of bone age after decomposition. Five chemical and physical tests can demonstrate this (Lengyel, 1963; 1965; 1967; 1969).

(1): Nitrogen content. Micro-Kjeldhal method. Nitrogen content diminishes with time interval. Bones under 50 years have a nitrogen content from 3.5g% to 5g%. A result of 2.5g% or less indicates 350 years or more.
(2): Amino-acid content. Thin layer chromatography method. Up to 14 may be present. Only Proline/Hydroxyproline identifiable (constituents of collagen). Seven or more gives an age of 70 to 100 years. Proline indicates less than 100 years.
(3): Fluorescence. Ultra-violet light. Across whole cut surface. Ndicates under 100 years. Incomplete fluorescence (increasing from periphery inwards) or traces only, indicates age up to 1800 years.
(4): Benzidine Reaction. Positive result indicates 100 to 150 years (liable to false results). Value of test in negative results. Negative means ancient.
(5): Immunological Activity. Gel-diffusion technique (anti-human serum). Ceases at an early age, after 5 years. Extreme limit is 10 years and under 20 years.

Summary of Tests.
Modern bone has a nitrogen content of 3.5g% or more; at least 7 amino acids (with pralines); complete fluorescence; with immunological activity present, indicates les than 20, but probably 5 or less. Ancient bone gives a negative Benzidine test. Considerations are waterlogged or dry conditions. Apatite crystals in bone increase in size with age interval. Methodology is the sterno-scan electron microscope.

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