Internal nautilus Oncocerida specimen cephalopod. The whole internal fossilised form with individual chambers filled with white calcite minerals is thought to be a member of the nautiloidea class of cephalopods. A fine example of the internal structure showing the chambers which have been replaced by quartz and calcite minerals over 420,000,000 to 355,000,000 years. The fossil excavated from the fossil site, cut out of solid rock, cleaned and semi-matt polished finish created by artisans in North Africa.
A siphuncle, a tube grew against the internal shell wall, this tube clearly illustrated in our images. It appears as a demi lune sectioned tube pattern on each chamber, along with the ventral curvature, the siphuncle passed gases and water from one ballast chamber to another to initiate rise and fall much like the ballast tanks of a submarine. As the nautilus grew the chamber became redundant but for buoyancy aids, using the gases it produced pumping them through the siphuncle to each chamber to regulate the cephalopods rise and fall in the water column. This siphuncle, like modern-day nautili, was also used as a jet propulsion system driving the cephalopod through the water, giving it speed and the element of surprise on ambulant bottom dwellers.
The largest chamber cavity is easily viewed as the wide end of the fossil sculpture, now the natural rock end or foot end of the sculpture, which is most apt, as the name cephalopod derived from the Greek (pod being a foot and kephale head, to Cephalon), cephalopod. Oncocerida is thought to be part of the nautiloidea subclass of cephalopods as described by Flower in 1950.
Sightings of the modern extant Nautilus Pompilius have been made off the Great Barrier Reef at depths between 200 to 400 meters, showing the pressures the Cephalopods can attain. Nautiloids are cephalopods as are the Ammonoidea class of shelled mollusc. The Ammonites extinction is dated around 65 million years. Ammonites are important index fossils, it is often possible to link the sediment layer in which they are found to specific geological time periods. The largest ammonite to date is around 2.5 meters in diameter from Germany.
Phylum: Mollusca, Class: Cephalopoda, Subclass: Nautiloidea, Order: Oncocerida, Family: undetermined, Genus: described by Flower 1950.