Fossil group

Corals (in limestone interbeds)

Corals · Ordovician – Recent

Marine cnidarians — relatives of sea anemones and jellyfish — that secrete a calcium-carbonate skeleton, as solitary cups or branching colonies. Reef-building corals need warm, clear, shallow water, so fossil corals mark ancient tropical shelves.

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