Fossil group

Ostracods

Arthropods · Ordovician – Recent

Tiny crustaceans whose body is enclosed in a hinged, bivalved carapace, often no larger than a sand grain. Abundant in marine and freshwater sediments, their shells are widely used as microfossils for dating rocks and reading past environments.

A broad fossil group rather than a single taxon — the units below record it among their fauna or flora.