Bone apatite

The 8 C values of the Preclassic humans at Cuello (Table 2.1) average -12.9 0.9%o (n = 28) in collagen, -9.8 1.0 in bone apatite (n = 16), and -8.7 2.3%o in tooth enamel apatite (n = 33) the S N values in collagen average 8.9 1.0%o (n = 23). The discrepancy in the number of specimens is due to the fact that more teeth were available than post-cranial material, while some of the specimens contained insufficient collagen to measure the nitrogen isotope ratios. Additional bone apatite analyses are in progress. 

Lee-Thorp, J.A., Sealy, J.C. and van der Merwe, N.J. 1989 Stable carbon isotope ratio differences between bone collagen and bone apatite, and their relationship to diet. Journal of Archaeological Science 16 585-599. 

Tykot, R.H., van der Merwe, N.J. and Hammond, N. 1996 Stable isotope analysis of bone collagen, bone apatite, and tooth enamel in the reconstruction of human diet. A case study from Cuello, Belize. In Orna, M.V., ed., Archaeological Chemistry Organic, Inorganic, and Biochemical Analysis. ACS Symposium Series 625, Washington, DC, American Chemical Society 355-365. 

Figure 3.2. 8 C values of fossil browser apatites plotted against age for sites including Die Kelders, Klasies River Mouth I, Sterkfontein and Makapansgat. Enamel is represented by solid squares, bone apatite by solid circles. The mean value standard deviation for modem browsers, represented by dashed lines, has been shifted by +1.5%o as described in the text. Adapted from Lee-Thorp and van der Merwe (1987).

For Klasies, although most values for both enamel and bone apatite fall within one standard deviation of the mean of (corrected) modem browser values (Fig. 5.5), some bone specimens fall outside this range. These enriched specimens suggest that a limited degree of equilibration with matrix carbonates has taken place, although inclusion of a limited amount of Q grass in the diet is a plausible alternative explanation for UCT 1025, Raphicerus sp. which as noted above could be the more opportunistic species, Raphicerus campestris. 

In the million year range, however, there is clearer evidence for isotopic alteration which also apparently increases with age. Unfortunately, at present there are few reliable browser and grazer data beyond the Late Pleistocene, i.e., in the Middle Pleistocene, which would allow determination of the periods during which bone apatite and enamel begin to deviate. The indications are that the timing should be different. Material from the site of Florisbad falls within the late Middle Pleistocene ( 125-200 Ka), but at present carbon isotope data are only available for three species of uncertain and/or opportunistic diets (Brink and Lee-Thorp 1992), so that extent or direction of isotopic alteration is impossible to separate from dietary vagaries. 

Hassan, A. A., Termine, J.D. and Haynes, C.V. 1977 Mineralogical studies on bone apatite and their implications for radiocarbon dating. Radiocarbon 19 364-374. 

Wheeler, E. J. and Lewis, D. 1977 An X-ray study of the paracrystalline nature of bone apatite. 

Wright, L. and Schwarez, H. 1996 Infrared evidence for diagenesis of bone apatite at Dos Pilas paleodietary implications. Journal of Archaeological Science 23 933-944. 

Kolodny, Y., Luz, B. and Navon, O. 1983 Oxygen isotope variations in phosphate of biogenic apatites, I. Fish bone apatite—rechecking the rules ofthe game. Earth and Planetary Science Letters 64 398 04. 

Ambrose and Norr (1993) and Tieszen and Fagre (1993) have shown that 5 C of carbonate in bone apatite (6 C,p) is the most accurate measure of the whole-diet composition (Ambrose and Norr 1993 28). The actual 5 C of total diet is related to that of apatite by an isotopic offset (fractionation) which Ambrose and Norr estimate to be 9.5 0.6%o. Other estimates range from 9.6 0.1%o for small mammals on controlled diets (DeNiro and Epstein 1978) to 12%o for large herbivores on natural diets (Lee-Thorp et al., 1989). The origin of this offset is of some concern to us here. We can only use 5 Cap as a measure of total diet if we know A,p.j,e, and also know that this fractionation is a constant, at least for a given species, and does not itself depend on the quality of the diet. 

Figure 10.2. Schematic diagram showing how restricted conversion of fatty acids to amino acids influences the fractionation between collagen and CO3 of bone apatite LI = lipid component, PR = protein, T = total isotopic composition AP = COj component of apatite, a) Herbivorous diet (Cj plants only) b) Carnivorous diet, assuming rj = 1 (no barrier to fatty acid conversion to AAs) c) Carnivorous diet, assuming ri < 1 note that carbonate-collagen fractionation is smaller.

The applicability of the linear-mixing model is seen most prominently in the interpretation of the 5 C of bone apatite which has been shown to represent the total diet, rather than being derived from energy foods , as was previously proposed by some authors. Although 5 C,p should represent total diet, the isotopic fractionation between this component and total diet appears to be somewhat variable, suggesting that more definite knowledge about this fractionation is needed if we are to use 5 C,p as an index of total dietaiy 5 C values. 

On the other hand, the scrambled model of carbon sourcing does not seem to be applicable when we consider the metabolic fate of fatty acids. We find that there are partial barriers to the movement of FA-derived carbon atoms into the synthesis of proteins. This partial restriction leads us to expect a trophic level effect in the fractionation between collagen and bone apatite or respired CO2 of which apatitic carbonate is a sample. The magnitude of the fractionation depends on two separate fractionation factors which cannot be disentangled by analyses of bone samples alone. 

Bj = The 8-value of the j -th component of any set of body components. For example, hone collagen bone-apatite carbonate total body lipid, total body glycine muscle glycine etc. Each particular choice will have its own distinct equation. The set need not be complete— unlike D. 

We make no attempt to discuss the partitioning behavior of U-series elements between aqueous fluids and minerals at ambient conditions. Examples where this behavior is important include uptake of U-series elements by cal cite in speleothems or by bone apatite. Also we do not consider U-series behavior in hydrothermal solutions at high temperatures, such as during dehydration of subducted crust. In both cases complexation behavior in the fluid may play an important role, and at low temperatures kinetic controls may dominate. These are fruitful areas for future experimental study. 

Johnson, K. (1997), Chemical dating of bones based on diagenetic changes in bone apatite, /. Archaeol. Sci. 24, 431-437. 

Hass, H., Banewics, J. J., Radiocarbon Dating of Bone Apatite Using Thermal Release of C02, Radiocarbon, 1980, in press. 

Figure 4.7 Measurement of crystallinity index from IR spectrum of bone apatite. Reprinted from Journal of Archaeological Science 17, Weiner, S. and Bar-Yosef, O., States of preservation of bones from prehistoric sites in the Near East a survey , pp. 187-96, copyright 1990, with permission from Elsevier.

Measurement of crystallinity index from IR spectrum of bone apatite 88... 

Kolodny Y, Luz B, Navon O (1983) Oxygen isotope variations in phosphate of biogenic apatites, 1, Eish bone apatite - rechecking the rules of the game. Earth Planet Sci Lett 64 393 04 Kolodny Y, Luz B, Sander M, Clemens WA (1996) Dinosaur bones fossils or pseudomorphs The pitfalls of physiology reconstruction from apatitic fossils, Palaeogeogr PalaeocUmatol Palaeoecol 126 161-171... 

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