Originating from within the bactritoid nautiloids, the ammonoid cephalopods first appeared in the Devonian (circa 400 million years ago) and became extinct at the close of the Cretaceous (66 Mya) along with the dinosaurs.
The Treatise on Invertebrate Paleontology (Part L, 1957) divides the Ammonoidea, regarded simply as an order, into eight suborders, the Anarcestina, Clymeniina, Goniatitina, and Prolecanitina from the Paleozoic; the Ceratitina from the Triassic; and the Ammonitina, Lytoceratina, and Phylloceratina from the Jurassic and Cretaceous.