I just read M.D.Gumert 2012 AJPA 149:447-457 "Marine prey processed with stone tools by Burmese long-tailed macaques": coastal macaques regularly use stone tools, and concluding: "In terms of diversity of foods exploited, coastal stone-based predation by macaques resembles the diet of coastal-foraging humans H.s.sapiens." I wondered whether they also had relatively (slightly) thicker tooth enamel than inland conspecifics or than non-tool-using macaques or other primates. Durophagy is typically seen in hard-object feeders, and we suggested that mid-Miocene hominoids (c 18-15 Ma) dispersed along peri-Tethys coastal forests, where they might have evolved thicker enamel & used stone tools for opening hard-shelled littoral foods, e.g. M.Verhaegen, S.Munro & P-F.Puech 2002 TREE Trends Ecol.Evol.17:212-7 "Aquarboreal ancestors?".