Clams build the reefs
Corals are pushed aside as strange conical bivalves take over the tropical shallows.
- When
- —
- Duration
- 64 million years
- Known to
- ± 5 million years
- Era
- Cretaceous, Mesozoic
Rudists are bivalves that abandon the shape of a clam entirely: one valve grows into a thick cone cemented to the seafloor while the other becomes a lid. Through the Cretaceous they crowd out scleractinian corals on tropical carbonate platforms and become the dominant reef builders, thriving in warm, saline, nutrient-poor water where corals struggle. The limestone they leave forms major oil reservoirs around the Gulf of Mexico and the Middle East. They vanish at the end of the period, and corals inherit the reefs again.