The kill-off pattern of domestic animals in archaeological faunal assemblages is most commonly established from deciduous and permanent tooth eruption and tooth wear patterns. During the last decades, however, the method of counting cemental incremental lines has been used on wild mammals, specifically to assess the time of seasonal settlement in archaeological materials. The method is relatively new and its potential is still being explored. Thus, further studies are needed to better define the accuracy, precision, sensitivity and specificity of the age assessment method of counting incremental lines in the dental cementum of domestic animals. The literature on this method is quite limited.
The overall aim is to develop and characterise an age assessment method based on incremental lines in dental cementum using contemporary bovine teeth and teeth from archaeological faunal assemblages. The investigations also include two other age assessment methods: tooth wear pattern and macroscopic dental measurements. The first permanent mandibular molar and lower jaws from 70 contemporary cattle of known age were made available for this study. In addition, 170 teeth from 170 animals and lower jaw molars when available from ten different Swedish archaeological sites were used. The following conclusions were drawn:
“Are there incremental lines in the dental cementum of cattle?” In transmitted polarised light, both distinct narrow light layes and wide dark layer were present in ground sections of teeth from medieval as well as contemporary cattle.
“Can incremental lines in the dental cementum of cattle be utilised for age assessment purposes?” The growth layers in teeth from medieval and post-Reformation cattle were more distinct than those of contemporary teeth. Thus, there appears to be a sound basis for age assessment of cattle of unknown ages based on incremental lines in dental cementum.
“Is there a relationship between the number of incremental lines and age in contemporary cattle?” and “Which part of the tooth root is the most reliable for age assessment based number of incremental lines in the dental cementum varied between different parts of the tooth root as well as within one and the same individual. The results from contemporary cattle of known age showed a strong relationship between age and incremental lines in the cementum of the distal part of the mesial root (R2=65.5%) and the known ages of the animals. The lines were thus interpreted as incremental lines related to age.
“Can the last formed cemental incremental line be used to identify the season in which the animal died?” There was no significant relationship between the appearance of the different parts of the incremental lines (dark or light) and the season of slaughter in contemporary cattle. This may be a consequence of the difficulty of correctly interpreting the outermost line in the ground sections.
“Do any other factors influence the formation of incremental lines in contemporary cattle?” With the “best” model variation in age could be explained to 65.5% (R2) by the number of incremental lines. Thus, the remaining age variation (approximately 35%) could not be explained by these lines. Other factors than must thus be responsible. However, with the exception of calves born the present material did not reveal any such significant relationship. In a larger material such factors could comprise stress, living conditions, climate, etc.
“How do other age assessment methods involving teeth compare with age assessment based on the formation of cemental incremental lines?” The results from cattle of known age indicate that the method of assessing age on the basis of cemental incremental lines is more reliable than other methods such as tooth wear or tooth measurements. However, by combining counting incremental lines and one variable assessing tooth dimension (tooth height) a slightly stronger relationship could be obtained (R2=74.5%).
“Can the methodological results from the contemporary material be applied to an archaeological material and if so, what are the limitations and possibilities of the methods?”
The results from age assessment of the medieval and post-Reformation cattle emphasize the importance of supplementing any age estimation of archaeological assemblages based on dental indicators with characteristics for the particular assessment model. Furthermore, conclusions based on age assessment with such models can not be drawn with any more detailed time scale than about 2 years leaving at best only 25% (R2) of factors influencing the dental indicator(s) utilized in the model unexplained. One such factor could be the number of calves given birth to. The accuracy of the age assessment required by the particular historical context in which the archaeological remains are found should thus decide what level of accuracy should be chosen.