Actinocerids first appeared early in the Middle Ordovician, with the exception of the Georginidae, which are known from the
Cassinian in Northern Australia. They reached their greatest diversity in the Middle Ordovician with more than 20 genera, then declined somewhat in the Late Ordovician and more so in the
Early Silurian; made a slight come back in the Middle Silurian but not to Late Ordovician numbers; and declined more or less steadily from the Late Silurian into the Devonian. Three major lineages began the Middle Ordovician, the Actinoceratidae, Armenoceratidae, and Ormoceratidae. The Actinoceratidae and Armenoceratidae are most likely derived from
Wutinoceras and the Ormoceratidae from a second wutinocerid genus,
Adamsoceras.
Gonioceras is an offshoot of an early Armenoceras;
Lambeoceras and
Huronia are offshoots of a later
Actinoceras. The Actinoceratidae extend into the Lower Silurian with
Actinoceras; the Armenoceratidae and Huroniidae extend into the Upper Silurian. The Ormoceratidae are possibly the most recent, extending into the Lower Devonian
Gonioceras (Gonioceratidae) is limited to the Middle Ordovician, its quasi-lookalike
Lambeoceras (Lamberoceratidae) to the uppermost Middle and Upper Ordovician. The wutinocerids are known only from the early Middle Ordovician (Whiterockian) and the polydesmiadids are restricted to about that time. Originating in the Ordovician, by the
Devonian period actinocerids became rare; they may have been unable to compete with the more compact and maneuverable coiled
nautiloids and ammonoids or cope with the arrival of jawed fish. == Classification and taxonomy ==