3. Methods

All the information and results presented here have been obtained from sedimentary samples (45 litres in total) collected during the excavation. Sieved with fine meshes (4 and 2 mm), these samples were sorted and studied at the Archaeosciences Laboratory of the University of Rennes. The identification of marine invertebrates (gastropods, bivalves and sea urchins) was carried out using the comparative collection from the same laboratory (comparative collection Gruet and Dupont, UMR 6566-CReAAH), and was confirmed using several reference works on marine biology (Tebble 1966; Poppe and Goto 1991; 1993; Hayward and Ryland 1995; Quéro and Vayne 1998; Audibert and Delemarre 2009). The scientific names used for the identified marine molluscs correspond to the international standards of the CLEMAM (2013). Several counting methods were used to calculate the relative proportions of each species. The NISP (Number of Identified Specimens) corresponds to all the identified remains greater than 2mm. The MNI (Minimum Number of Individuals) was also used. For bivalves, an MNI was obtained after assigning valves to the left or right according to the position of the teeth, the ligament and the pallial sinus line (Dupont 2006a; McCarthy et al. 1999). For spiral gastropods, the MNI is linked to the presence of the peristome (Dupont 2006a). Finally, the remains of each species were weighed (in grams).

The shells were then measured using a digital calliper graduated in millimetres (mm) (0.01) in accordance with the procedures described by Dupont (2006a). Some specific biometrical studies were also performed on the common mussel (Mytilus edulis). Shells found at the site are highly fragmented and consequently the whole length is not measurable. In fact, their fragile nature meant that the shells were found crushed as a result of the mechanical pressure exerted by the overlying sediments. Some authors highlight the fact that a good correlation exists between the height and the length of the shell (Buchanan 1985; Dupont 2006a, 86-87; Campbell 2013) and that it is therefore possible to reconstruct a mussel original size from measurements of shell height. However, mussels discovered at the Clos des Châtaigniers were so fragmented that shell height could not be measured. Therefore, a different method was employed, relying on a correlation established between original mussel size and a small part near the teeth (corresponding to the not pearly part, located just after the anterior adductor muscle scar; see Figure 4) (Mougne in prep). Through taphonomic analysis, modifications due to physical and chemical factors on the archaeomalacological material were identified (Claassen 1998; Dupont 2006a; Gutiérrez Zugasti 2008). The associated faunas in the thickness of the shell and in or on the shells were also observed and recorded (Hayward and Ryland 1995).