AbstractNew exavations of the Mesolithic shell midden type locality, Ertebølle, Denmark have given access to well preserved cockle and foraminifera shells sampled 5700–5230 (± 95) years before present. Species and ecotype determinations of Cardium (Cerastoderma) edule (L.) and Cardium lamarcki (Reeve) revealed sea exp.sure and salinity conditions suggesting existence of a sheltered low salinity lagoon within range of the settlers during part of the period. This was further supported by the foraminifera species composition. An indication of the Littorina Sea temperature at the settlement was obtained from comparisons of midden material with present material concerning C. edules hell sizes and species specific growth rates for sympatric C. edule and C. lamarcki combined with the species composition of foraminifera. These studies do not support theories suggesting that the Littorina Sea temperature conditions differed substantially from those found in the area at present.