1 The Early Bronze Age Log Coffin Burials of Britain: The Origins and Development of a Burial Rite(s) By Richard Brunning, Seren Griffiths and Andy M. Jones APPENDIX S1: RADIOCARBON MODELLING Here, for the two sites that warrant site specific chronological models we present this analysis. We also include an alternative approach to analysing all the legacy data. In this we have grouped results from sites using Needham’s periodisations (Needham 1996) for the British Bronze Age, together with revisions to this model which include other artefact forms (Needham 2009; Needham et al. 2010; Woodward & Hunter 2015, 461–71). We discuss this approach below. All these models apply Bayesian analysis in the program OxCal v4.3 (Bronk Ramsey 2009; 2017; Bronk Ramsey & Lee 2013). We have analysed these measurements using the calibration data of IntCal20 (Reimer et al. 2020). The OxCal CQL2 commands and the brackets shown in the figures define the models; the OxCal CQL2 commands in the text below are quoted by convention in Courier font. The date ranges quoted below in italics are the Highest Posterior Density intervals derived from these Bayesian models. They are quoted at 95% probability, unless otherwise stated. Site specific models For two sites, Gristhorpe and Piper Hole Farm, we have sufficient radiocarbon measurements to produce site‐specific chronological models. We discuss these site‐specific models here, before introducing our analysis of the dataset as a whole. Gristhorpe results: At Gristhorpe, sufficient measurements exist on the coffin to produce a Bayesian ‘wiggle match’ (Christen & Litton 1995; Galimberti et al. 2004). Wiggle matching combines a group of radiocarbon measurements produced on tree rings that are separated by a known number of additional annual tree rings. The radiocarbon measurements can then be ‘matched’ to the shape of the radiocarbon calibration curve. A 173‐year composite sequence from the coffin was sampled by six radiocarbon measurements at Gristhorpe (Batt 2013). Each of these measurements was produced on a sample of a block of ten annual rings. The interval between the mid‐points of each sample and the next sample was 30 years. After the youngest dated sample from this timber there were 20 sapwood rings. We can use this prior information to slightly revise the wiggle match produced in the original publication Batt (2013; Fig. S1). The results from this model have good overall agreement (Agreement n=6; Acomb= 89.7%; (An= 28.9%)). The last ring preserved on the Gristhorpe log coffin wiggle match sequence formed in 2050– 2010 cal BC (93% probability or 1975–1960 cal BC 3% probability; Year 0+20 sapwood; Fig. S1). To provide an estimate of the felling date of the timber we need to have an estimate for the number of additional sapwood rings present if 20 sapwood rings were preserved on the timber. Bayliss and Tyers (2004, 961) provide a methodology for this process, which provides an estimate for the felling date of 2050–1995 cal BC (92% probability or 1980–1950 cal BC 3% probability; felling estimate; Fig. S2). Two additional results from the site were produced from the burial; a measurement on the tooth dentine (OxA‐16844) and from the femur (OxA‐19219). Teeth form in childhood, whereas long bones gradually remodel over the lifespan of an individual (eg, Sealy et al. 1995; Hedges et al. 2007). The measurement on the tooth should therefore, in radiocarbon terms, be older than that on the long bone. Furthermore, the long bone would be older in radiocarbon terms than the date of death of the individual, as remodelling of such robust elements occurs over several decades. If the timber for the coffin was felled specifically for the burial, and not stockpiled, the felling date too should be younger in radiocarbon terms than the measurement on the femur. We have presented the measurement on the