3.05" Cretaceous Fossil Oyster (Rastellum) - Madagascar

This is a Cretaceous-aged fossil oyster of the species Rastellum carinatum from Mahajanga Province, Madagascar. It has wide, angled ribs that evoke its nickname 'denture clam'. The zig-zag joint between the two shells stopped coarse dirt and debris from 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.