Editing Ammonoidea (section)

==Classification==
{{see also|List of ammonite genera}}
[[Image:Ammoniteplit.jpg|thumb|An ammonite shell viewed in section, revealing the internal chambers and [[Septum (cephalopod)|septa]]: Large polished examples are prized for both their aesthetic and scientific value.]]

=== Orders and suborders ===
[[Image:1212amma.jpg|thumb|An ammonitic ammonoid with the body chamber missing, showing the septal surface (especially at right) with its undulating lobes and saddles.]]
[[Image:Iridescent Ammonite Fossil.jpg|thumb|[[Iridescence|Iridescent]] ancient ammonite fossil on display at the [[American Museum of Natural History]], New York City, around 0.61 metres (2 feet) in diameter]]

The Ammonoidea can be divided into six orders, listed here starting with the most primitive and going to the more derived:
* [[Agoniatitida]], Lower Devonian – Middle Devonian
* [[Clymeniida]], Upper Devonian
* [[Goniatitida]], Middle Devonian – Upper Permian
* [[Prolecanitida]], Upper Devonian – Upper Triassic
* [[Ceratitida]], Upper Permian – Upper Triassic
* [[Ammonitida]], Lower Jurassic – Lower Paleocene

In some classifications, these are left as suborders, included in only three orders: [[Goniatitida]], [[Ceratitida]] and [[Ammonitida]].  The classification of ammonoids is based in part on the [[Biological ornament|ornamentation]] and structure of the [[Septum (cephalopod)|septa]] comprising their shells' gas chambers.

=== Taxonomy of the ''Treatise on Invertebrate Paleontology'' ===
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. In subsequent taxonomies, these are sometimes regarded as orders within the subclass Ammonoidea.