Plectronocerida
Plectronocerida Temporal range:
| |
---|---|
Plectronoceras life restoration | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Mollusca |
Class: | Cephalopoda |
Subclass: | Nautiloidea |
Superorder: | †Plectronoceratoidea |
Order: | †Plectronocerida Teichert, 1988 |
Families and genera | |
Plectronoceratidae Balkoceratidae |
Plectronocerida is a primitive order from which subsequent
Occurrence
Plectronoceratids are known from the Upper
Diagnostic characters
Members of the Plectronocerida are characterized as follows. Shells are generally small, some even tiny, laterally compressed, curved (cyrtoconic) or straight (orthoconic). Most cyrtoconic forms are endogastric, with the ventral side longitudinally concave, or the dorsal side more longitudinally convex. A few, the two known genera in Balkoceratidae are exogastrically curved, with the ventral side convex and dorsal side concave. Septa are close spaced, in some less than a millimeter. Siphuncles are ventral, and in most, proportionally large. Connecting rings are in general poorly calcified and may expand as siphonal bulbs into the chambers where not restricted by septal necks.[3]
As with all shelled cephalopods, plectronocerids had a tube called a siphuncle, which let them fill the chambers of their phragmocone with gas instead of water, thus controlling their buoyancy.[4] They were not, however, adapted for jet-powered swimming.
Phylogeny
The Plectronoceratida gave rise in the
Ecology
Plectronocerids were probably
References
- .
- ^ Curt Teichert, 1988. Main Features of Cephalopod Evolution. The Mollusca Vol. 12 Paleontology and Neontology of Cephalopds; Academic Pres Inc.
- ^ a b Flower, Rousseau H. 1964. The Nautiloid Order Ellesmeroceratida (Cephalopoda); Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico
- .
Further reading
- Flower, Rousseau H. (1955). "Saltations in Nautiloid Coiling". Evolution. 9 (3): 244–260. JSTOR 2405647.
- Furnish, W.M.; Glenister, B.F. (1964). "Nautiloidea - Ellesmerocerida". Treatise on Invertebrate Paleontology. K: K129 –.