A crystallised Nautilus 80mm exhibiting subtle opalescence where the remaining nacre of mineralised shell is still attached. The chamber of the phragmacone (shell) are filled with a quartz minerals in the form of calcite and jaspers. These minerals grow within in the hollow cavities left behind post the cephalopods demise. Gaseous chambers under the right conditions allow the formation of crystals.
The shell entombed in the bottom mud's from the Cretaceous seabed, a process of osmosis takes place, water coursing through the local environment over time, saturated with minerals seeps through the tissues of the shell and any animal remains, this process is per-mineralisation and this transforms the shell into the fossil we see here. Any mineral wealth around the fossil bed or fossil layer formations, post an event of mass mortality of animals due to some catastrophy become petrified and mineralised in this way and eventually over a long period, fossilised.
Nautilus were once long ago in the Devonian period closely related to the Ammonites, the family tree split some 400 to 350 million years ago and the Ammonites developed a quite unique lineage apart from the Nautiloids. It is thought this is why we still have nautili swimming our oceans today while the Ammonites died out between 74 to 64 million years ago. Ammonites it is now theorised evolved to be less aggressive deep sea hunters, their main prey being platonic at the surface of the oceans, this put them at risk of climatic changes. As the Cretaceous period came to an end, due to environmental changes and eventually a catastrophic event which put pay to the dinosaurs on land, the KT boundary event, the climatic change also reduced the Ammonites main food source plankton, possibly sending the Ammonites into a spiral of decline.
Nautiloids are benthic, swim between mid depth to deep levels. It is theorised this sets them apart from the ancient Ammonites, as palaeontologists have found Ammonites in shallow levels of the sea enviroments within the fossil record. Also nautiloids give birth several times during there lifespan, where as Ammonites once at the end of life, therefore the nautiloids had a better chance of surviving. Even though the Ammonites were much more prolific and successful for most of their existence.
The Nautilus shell of today is quite thick in comparison to the prehistoric Ammonites shells, the Ammonites sacrificed a defensive shell for a lightweight thinner shell, creating features like exotically frilly sutures to spread strength, giving them ultimately more stealth. However this could have been a disastrous development ultimately as populations decreased and climatic condition changed drastically, predation on the Ammonites could have increased. Whereas the Nautiloids could seek deeper levels in crisis and thicker shells gave them more of a chance against predators.
This fossil Nautilus originates from the Tulear region of Madagascar and dates back to the Mesozoic era, specifically the lower cretaceous period, approximate dates, 99-112 million years. Nautilus still persist in the modern oceans of the world, living at great depths, the only surviving relatives of the coiled cephalopods which evolved over 400 million years ago. Sightings of the modern extant Nautilus Pompilius were made off the Great Barrier Reef at depths between 200 to 400 meters, showing the pressures these Cephalopods can attain. 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.
Originating from the Tulear region of Madagascar and dates back to the Mesozoic era, specifically the lower cretaceous period, approximate dates, 99-112 million years.