Nautiloidea (original) (raw)
illustration from Fenton & Fenton, The Fossil Book,
1958, Doubleday & co., p.182
1. Gonioceras (Ordovician) - Actinocerida, 2 Heracloceras (Devonian)Barrandeocerida,
3. a very implausible Cyrtoceras (Silurian) Oncocerida (it is possible that ancestral Plectronocerids did still retain a snail like locomotion), 4. Michelinoceras (Silurian) - Orthocerida,
5. Mandaloceras (Silurian) Discosorida,
Introduction
The "Subclass Nautiloidea" refers to a broad assemblage of molluscs that includes all Cephalopods other than Ammonoids and Coleoids.
Appearing during the late Cambrian they evolved into a great diversity of forms and lifestyles, as indicated by the amazing range of shell types and structure (see illustration above). Remaining diverse throughout the early to mid Paleozoic, they declined later in the era, and have remained relatively unimportant ever since. There are only 3 or 4 living species, all belonging to the single genus Nautilus (the pearly nautilus),
Physiology
graphic from
Lake Témiscamingue Fossil Centre
Nautiloids possess of an external shell divided into chambers by walls known as septa. Contact between septa and the shell wall produces suture lines, often visible in fossil forms. The animal lives in the outermost chamber, called the living chamber. Nautiloids are distinguished from the very similar Ammonoids by the simple nature of the suture lines, and a siphuncle located usually along the center of the shell. Key features which are very important in nautiloid classification are the internal and external structure of siphuncle and the type of internal (cameral and siphuncal) calcareous "ballast" deposits.
Systematics
Despite appearing in text books for many decades, the term Nautiloidea is now considered taxonomically useless. Many controversies arose which characters can be used for classifying subclasses, orders, families and genera. Characters were not investigated according to cladistic or phylogenetic relationships, and often were quite arbitrary. Different researchers came up with totally different classifications. Generally, Nautiloidea is retained as a general catch-all for all cephalopods that are not ammonoids or coleoids. However the subclass Nautiloidea does appear to be partially equivalent to the paraphyletic group "Palcephalopoda."
More than 270 families of Nautiloidea are currently known, about 1750 genera, and some 9000 species. No doubt there are innumerable more waiting to be discovered, or species that never fossilized.
Nautiloid Groups
Subclass: Palcephalopoda
Infraclass unnamed ("Ellesmeroceroidea"? or several infraclasses?)
Order Plectronocerida Flower, 1964
Order Yanhecerida Chen & Qi, 1979 (or included in Plectronocerida or Ellesmerocerida?)
Order Protactinocerida Chen & Qi, 1979 (or included in Plectronocerida or Ellesmerocerida?)
Order Ellesmerocerida Flower, 1950
Order EndoceridaTeichert, 1933
Order Injetocerida Balashov, 1960 (or included in Endocerida?)
Order Discosorida Flower, 1950
Order ActinoceridaTeichert, 1933
Order Pseudorthocerida
Infraclass Nautiloidea Agasiz, 1947 (= Nautiloidea "strictu sensu")
Order Tarphycerida Flower, 1950
Suborder Tarphycerina Flower, 1950
Suborder BarrandeocerinaFlower
Order Oncocerida Flower, 1950
Order NautilidaAgassiz, 1847
Subclass: Neocephalopoda
Infraclass Orthoceratoidea Kuhn, 1940
Order Orthocerida Kuhn, 1940
Order Ascocerida Kuhn, 1949
Links
Fossil Nautiloidea Page - The Page for People Interested in Fossil Nautiloidea - if, like me, you share an interest in the technicalities of this group of extraordinary invertebrates, this is the definitive site to go to. Created and maintained by Theo Engeser
The Orthoceras Nautiloid - a few notes on nautiloids - Lake Témiscamingue Fossil Centre
Glorantha Nautiloidea - this has nothing to do with science - it is a strange page on the history of the nautiloids in Glorantha, a Nordic-type fantasy world created by Greg Stafford (originally a board game, later a role-playing game). Although it has nothing to do with serious knowledge of nautiloids, I thought I would put it in anyway)
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page uploaded 27 September 2002
checked ATW020930
(originally uploaded on Kheper Site 1998)
text by M. Alan Kazlev 1998-2002
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