1.9" Cretaceous Fossil Oyster (Rastellum) Half - Madagascar

This is a Cretaceous-aged fossil oyster of the species Rastellum carinatum from Mahajanga Province, Madagascar. It had wide, angled ribs that have lent it the nickname 'denture clam'. The zig-zag joint between the two shells stopped coarse dirt and debris entering the shell and damaging its soft body. Like modern oysters, it lived in shallow coastal waters including the intertidal zone--the area between high and low tide--and fed on food particles that it filtered out of the sea water.