Fossil Bivalves
Clams, oysters, scallops, and mussels — bivalves have filtered the world's oceans for 500 million years and are among the most abundant fossils in marine sediments.
Overview
Bivalves — clams, oysters, scallops and mussels — are molluscs with two lateral shells hinged by teeth and an elastic ligament. Simple, tough and hugely successful, they are among the most abundant fossils in marine sediments from the Cambrian to today.
Quick Facts
Key Characteristics
- •Two mirror-image left and right valves joined at a dorsal hinge
- •Teeth and sockets interlock the valves; ligament opens them
- •Most filter-feed using enlarged gills; many burrow, cement or byssally attach
- •Growth lines on the shell record age, season and stress events
- •Rudists replaced corals as reef builders in parts of the Cretaceous
Fossil Record
Shells preserve abundantly — Gryphaea 'devil's toenails' define Jurassic clays; oyster reefs carpet Cretaceous and Cenozoic beds; aragonitic shells sometimes dissolve leaving internal and external moulds.
Global Distribution
Global — every marine basin through the Phanerozoic yields bivalves, with world-famous Jurassic and Cretaceous faunas in Europe and North America.
Evolutionary & Scientific Importance
Bivalves are essential palaeoenvironment indicators (salinity, energy, substrate), key Mesozoic index fossils, and their shells archive long-term climate in their growth bands.