Metrical variation between populations of Discus rotundatus as a palaeoecological proxy: a 2D geometric morphometric approach and its archaeological implications Matt Law, School of Sciences, Bath Spa University m.law@bathspa.ac.uk RATIONALE Discus rotundatus (Figure 1) is one of the most commonly encountered land snail shells in archaeological assemblages from Great Britain (Evans 1972, 185). It is variable in its shell geometry, and in many species this variability is linked to environmental factors. Kuznik-Kowalska (2008) found variation within laboratory-reared D. rotundatus (66 shells) was much more marked than in wild populations, which she attributed to lower selection pressure. Kappes et al. (2009) found that age of habitat and degree of reafforestation seemed to impact shell shape. Shells from reafforested sites had wider apertures, smaller embryonic shells and greater heterogeneity in shell metrics than those from unchanged or fragmented sites. It was suspected that the changes may be attributed to the fact that calcium availability is temporarily higher in young regrowth forests, and that newer forests are situated on rich, loamy soils. A geometric morphometrics (GMM) approach has been taken because of the opportunity it allows to measure small but significant geometric differences in the overall shape of the shells that may not be recorded by linear measurements. HYPOTHESIS Variation in shell geometry between populations of the land snail Discus rotundatus are environmentally determined, and can be used as a palaeoecological proxy. FINDINGS Initial results suggest that there is a greater deal of heterogeneity of shell geometry in mature woodland sites than the more open sites (Figure 2). Principal components analysis suggests that the Ruishton shells somewhat cluster, as do the Newton Park shells, whereas the Little Whittenham and New Zig Zag shells show far more variation. NEXT STEPS More data are being collected from Little Whittenham and also from mature woodland at Newton Park. Shells are also undergoing traditional metrical analysis alongside GMM. Possible correlations between shell variation and soil pH and rainfall will also be investigated. Finally, archaeological assemblages will be analysed. Acknowledgements This work is funded by a research grant from the Conchological Society of Britain and Ireland. References Evans, John G. 1972. Land Snails in Archaeology. London: Seminar. Kappes, Heike, Kurt Jordaens, Natalie Van Houtte, Frederik Hendrickx, Jean-Pierre Maelfait, Luc Lens, and Thierry Backeljau. 2009. ‘A Land Snail’s View of a Fragmented Landscape’. Biological Journal of the Linnean Society 98 (4): 839–50. https://doi.org/10.1111/j.1095-8312.2009.01321.x. Kuznik-Kowalska, E. 2008. ‘Shell Variation in the Genus Discus Fitzinger, 1833 (Gastropoda: Pulmonata: Endodontidae)’. Folia Malacologica 1 (16). https://www.infona.pl//resource/bwmeta1.element.agro-7eae9cd0-be85-4b87-a926-34c8385715b4. Law, Matt. 2023. ‘Methods in Archaeomalacology: Two Dimensional Geometric Morphometrics Of Gastropod Shells’. Archaeo + Malacology Newsletter, no. 39: 11–18. Figure 1: Discus rotundatus. Shell diameter= 5.4mm Figure 2: Principal components analysis of Procrustes distance matrix for all shells. PC 1 eigenvalue = 0.8; PC 2 =0.1 MATERIALS AND METHODS So far: 57 modern shells from 4 sites in southern England. Two are in mature woodland: Little Whittenham, Oxfordshire (LW1: 51.630274, -1.1797967) and New Zig Zag, Bristol (NZZ: 51.461337, -2.6296043). The other two are more open environments, an agricultural field margin at Ruishton, Somerset (RUI: 51.016001 , -3.0570831) and managed gardens at Newton Park, Bath (NPQL, NPCE and NPIG: 51.373405, -2.4412011). Shells were photographed in apertural view using an identical set up in each case. Two-dimensional geometric morphometrics was then carried out using semilandmarks following the procedure outlined by Law (2023), using the software packages tpsDIG2, Notebook ++ and MorphoJ.