The researcher Abel Moclán, of the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), has participated in a study led by Héctor Del Valle of the IPHES-CERCA, and published in the prestigious Journal of Archaeological Science, which shows that animal dung burning processes had an important impact on the composition and fossilization of archaeological bone remains, and this has proved key to understanding the conservation of the materials at the El Mirador cave site (Sierra de Atapuerca, Burgos).

This site has been under excavation since 1999, providing a sequence with Pleistocene and Holocene levels, and is indispensable in particular to understanding the commencement of agricultural or livestock practices in the Iberian plateau. This paper represents the first study of bone diagenesis in fumiers at El Mirador, furnishing important conclusions about the formation of this kind of sequence, generated by livestock activities in caves used as stables from the Neolithic.

According to Del Valle, “[It] can be concluded from the study that the sedimentary context of each fumier facies leads to specific characteristics in the composition of the bone remains, and the origin of the bones can be discovered on the basis of these [AMR2] characteristics”. So, it is possible to select the best-preserved facies and, therefore, select the most viable ones for obtaining data of biochemical origin such as proteins or isotopes.

For more than 4000 years, the cave was used as a place of habitation, a grave and stable for livestock. This latter activity generated a sedimentary deposit made up of animal dung, plant remains and waste from human occupations. These deposits were burned to kill parasites and clean the spaces, yielding a series of layers (facies), both burned and unburned, which make up the fumier, with the El Mirador one being one of the largest and best conserved from its period.

These deposits are a source of high-quality information of granular time resolution for revealing details of the expansion and development of agricultural and livestock prehistoric producer economies, from their area of origin in the Middle East as far as the Iberian Peninsula.

New techniques and methods

The study shows that, using the ATR-FTIR technique, but irrespective of sound external appearance, bone remains must be evaluated for their state of conservation at molecular level to be known. This makes it possible to choose samples whose components are best preserved, for other analyses.

Another contribution of the work is the use of new statistical methods like Artificial Intelligence. These analyses enabling classifying the origin of the bone remains in the different facies, and highlighting that bones acquire different properties on foot of their carbonates content. This is of special interest in the case of unburned facies which have been reelaborated, by distinguishing unburned bones which are similar in appearance.

In summary, the study has offered data on the formation of fumiers, the impact of fire on bones, and the characteristics these acquire in each facies. These results could be applied to other Neolithic assemblages in the Mediterranean basin with fumier sequences