Stable isotope ratios of bone constitutive elements (including C, N, O, Sr and S) inform about the individual’s diet, and the landscape, climate and geology of its habitat.

Isotope analyses performed in bone and teeth (photo M. Balasse).

Ingested from food and drinking water, these elements are incorporated into bone tissues during skeletal development. In bone, they are then renewed throughout life while tissues turnover: for this reason they mainly reflect the last part of the existence. In dental tissues (dentine and enamel), which are not remodeled, information are fixed during tooth formation, over the first years of life (except in species with ever-growing teeth). Under certain conditions, biogenic isotope ratios are preserved and can be measured. Therefore it is possible, not only to extract palaeodietary and palaeoenvironmental information from skeleton remains, but also, by comparing isotope signals incorporated in different pieces at different times of life, to reconstruct sequences of individual history.

This last point is of particular interest for archaeozoology and especially the study of herding practices and techniques.

Tooth enamel sequential sampling (photo M. Balasse).

Studies of intra-tooth variations of isotope ratios has considerably developed over the past few years. They are most frequently conducted on enamel bioapatite (mineral fraction) on which analysis of d13C, d18O and 87Sr/86Sr is performed. However a few studies have also been conducted on the d15N and d13C values of dentine collagen (organic fraction). Tooth is sampled sequentially following growth axis, in order to observe variations in the isotope signal recorded during tooth formation. The geometry of growth and mineralization process of dental tissues are very complex, however it seems that that sampling procedure preserves chronology.

Application of the procedure permits to deal with topics such as:

	weaning age of domestic animals (and, indirectly, investigation of duration of lactation);
	seasonality of birth of domestic animals;
	animal diet (winter foddering);
	seasonal mobility of herds.

The sample size required for isotope analysis has been considerably reduced, opening new perspectives of application. It is now possible to measure d13C and d18O values of very small amount of material sampled along growth lines in shells and fish otholiths, allowing climatological investigations, and determination of gathering and fishing season.

While applications to ancient material is gaining popularity, enlargement of modern reference sets is still seriously needed.