Fossil group

Ammonoids (rare)

Molluscs · Devonian – Cretaceous

Extinct shelled cephalopods with chambered shells and distinctively folded internal walls (sutures), spanning the ammonites and their Palaeozoic–Triassic forebears. Their fast evolution and wide dispersal make them prime index fossils from the Devonian to the end-Cretaceous.

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