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Geographic diversity of Neandertals in Europe

Final Report Summary - NEAND-GEOGR-DIV (Geographic diversity of Neandertals in Europe)

Neandertals lived in Eurasia for more than 200 000 years and represent the closest relatives of present-day humans. Their study helps us understand what makes modern humans so unique and evolutionary successful. We proposed to apply novel analytical methods to provide new information on the biological and behavioural diversity of the Neandertals in order to better understand how the colonisation of European territory and its ecogeographic characteristics has influenced their evolutionary history. More specifically, we proposed to investigate the morphological diversity and mobility patterns of Neandertals from four geographic regions in Europe.

Their morphological variation are assessed using frequency distribution of discrete skeletal traits (skeletal features such as tubercles, grooves, foramina that are commonly used in the study of recent human populations, as an indicator of population history), whereas we use strontium isotope analysis to study their mobility patterns and territorial strategies. Indeed, the strontium (Sr) in dental enamel comes, through the diet, from the Sr of the bedrock and soil. The Sr is incorporated into dental enamel during tooth formation in childhood and is then preserved into the teeth. The ratio of two isotopes [87Sr/86Sr] reflects the local geology as it varies according to the mineral composition and age of the rocks. When the Sr passes through the diet, there is no change in the 87Sr/86Sr ratio. Thus, this ratio in the enamel allows determining the geographical location where the individual lived during the period of tooth formation. The application of strontium isotope analyses to fossil hominins is a very new field of research and applies state-of-the-art methods in biogeochemistry.

Our objectives were:

(1) to perform an investigation of discrete traits frequency distribution and decipher patterns of similarities and divergence between geographic groups;
(2) to investigate mobility patterns and territorial strategies and their possible regional diversity;
(3) to compare and synthesise the information obtained by both sources of data in each region and discuss their insights into regional peopling history by Neandertals and inter-populations relationships.

These objectives have not been fully achieved because the researcher, Christine Verna, obtained a permanent position at the CNRS in France starting on 1 February. The Marie-Curie IEF was consequently stopped on 31 January, before the final objectives of this project could be fulfilled.

During the reporting period, our efforts have been put in collecting data for both morphological and isotopic analyses. The database structure for morphological analyses was build during this period. After a comprehensive review of the literature, a total of 94 cranial discrete features were selected and for each, a scoring procedure was established. This step also required complementary training in skeletal anatomy that were done through the interactions with the members of the department (Prof. Rosas and Dr Bastir in particular). In addition, a database recording an inventory of Neandertal fossil remains was build. It includes for each specimen the name of the archeological site, its GPS coordinates as well as the chronological and archaeological context in which the remains were found. A total of 717 Neandertal specimens as well as 321 isolated teeth are currently included in this database.

After this first step, we started to fill the database by scoring morphological discrete features on original Neandertal specimens. A very important part of this step is the inclusion of all the material found at the site of El Sidrón, which is curated in the Department of Paleobiology in Madrid. A total of 57 cranial remains, 17 mandibles and 6 maxillas found at this site were screened and their discrete features scored in the database. Additional Neandertal original remains studied during this period are the specimens from Saint-Césaire (France) and Ehringsdorf (Germany).

We also started to collect the isotopic data needed for the development of the project, by analysing Neandertal remains from Southwestern France. The region of Poitou-Charentes in France has indeed yielded many remains of Neandertals who occupied this region for more than 200 000 years. Through strontium isotope analyses, we then have the the opportunity to study individual, group as well as diachronic variability in mobility patterns. We selected three archaeological sites (Rochelot, Abri Bourgeois-Delaunay and Abri Suard) that yielded series of isolated teeth. The sites are located in the Charente Basin, and are caves opened in the Mesozoic limestones of the Aquitain basin. The measurements of the Sr isotope ratio in the dental enamel of these specimens were done at the MPI-EVA in Leipzig.

We provide here the results obtained for an individual found at the site of Rochelot. Six teeth were analysed and yielded a measurable 87Sr/86Sr signal fulfilling our quality criteria. Two teeth that were formed early in the life of the individual (lower canine and first molar) yielded a 87Sr/86Sr ratio similar to the local limestone deposits (see the figure below). Two other teeth (upper first and second premolars), that are formed later in infancy (likely sometime between two and four years old), yielded however a high 87Sr/86Sr ratio, that falls outside the known range for the regional Mesozoic limestones. This shows that the Neandertal from Rochelot incorporated for a certain time in his diet food ressources coming from another geological background, likely the Paleozoic crystalline rocks that are found some 30 kms East of the site. The two last teeth that were formed (lower second molars) show again a 87Sr/86Sr ratio similar to the two first teeth and to the Mesozoic limestones, suggesting that the group moved again or returned to the same geological background. Together, these data indicate that the individual from Rochelot has likely spent some time in another region than where he was found (sometime between 2 and 4 years), and also suggest for the group at least two residential moves between 0 and 6 - 8 years.

These very promising results show how strontium isotope analyses can give us information about food provenience during childhood and a new line of evidence for assessing Neandertal group mobility and territorial strategies. A public lecture presenting the use of strontium isotope analyses to assess Neandertal mobility- including our first results obtained during this reporting period - was given in January 2012 in Paris.

On the other side, during the period, a talk was given at the International meeting of the Society for the Study of Human Evolution (Leipzig, Germany, September 2011) presenting the results of the study of a Middle Pleistocene mandible recently found in France. The morphometric analysis of this specimen, and in particular, the morphological discrete features of the mandibular body, led us to question the definition of the taxon Homo heidelbergensis, and to discuss the morphological diversity of the earliest Neandertals. In January 2012, a poster was presented at the meeting of the Société d'Anthropologie de Paris (in Bordeaux, France) showing the results of a study of human remains found at the site of La Quina-Aval (France). Our morphological analyses of these specimens allowed us to show that the makers of the Early Aurignacian technocomplex in France were anatomically modern humans and not Neandertals, contrary to what had been recently suggested by various authors.

Finally, from an institutional viewpoint, even thought the project has been prematurely interrupted, thanks to the stay at the Department of Paleobiology of the Museo Nacional de Ciencias naturales, Christine Verna is however able to pursue this project in collabouration with A. Rosas. In fact, Dr Verna has become a member of the Spanish Science Minister Grant number CGL2012-36682 for 2013 - 2015.

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