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Holzmaden Ammonoid Plate 4ft


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An exquisite Holzmaden fossil ammonoid Poseidon shale plate encapsulating Harpoceras and Dactylioceras ammonoids which have absorbed mineral deposits during the fossilisation process over 180,000,000 years. Read more below...

Genus: Harpoceras falcifer and Dactylioceras commune Family: Cephalopoda, Order Ammonitida, Family Hildoceratidae and Dactylioceratidae.
Origin: Holzmaden region, Posidonia formation, Lagerstätten shales, South West Germany.
Age: Palaeozoic era, Lower Jurassic period, Toarcian stage, approximately 180 million years. Holzmaden plate measurements.

Holzmaden Plate Measurements.
Height: 105.5 cm
Width: 122 cm
Depth: 2 cm

Weight: 45 Kg


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Holzmaden ammonoidea plate, beautifully curated for interiors around the world. The Harpoceras ammonite exhibiting exquisitely detailed preservation with conservation of the fossilised Jurassic phragmacone (shell), once the home of a marine mollusc a cephalopod member related to modern-day cuttlefish and octopi of the cephalopoda group. The Harpoceras ammonite being part of the subclass Ammonoidea and a family Hildoceratidae. The extinct prehistoric molluscs shell has absorbed, through a process of an anoxic environment (lack of oxygen) in conjunction of a lack of organic bacterial growth, Iron pyrite has formed from the production of sulphur from simple algae. This caused an iron pyrite metamorphism to the decaying animal and shell during the fossilisation process, which has taken place over 180,000,000 years, the minerals of iron pyrite have developed in the form of the more commonly known fools gold. Fools gold is often found in the occurrence of gold ore and is used as an indication of a possible gold seam.

The surrounding shale has been carefully and precisely cut and fashioned from the fossil bed, prepared and finally conserved providing a fine naturalistic and aesthetically pleasing statement wall piece. The fossil inclusion within the plate is the natural fossil from the fossilisation of marine cephalopoda. Each fossil phragmacone exoskeleton (shell) demonstrates excellent detail; all the specimens feature fine ribbed and sizeable sized phragmacone's of type.

The Posidonia shales of the Jurassic (Toarcian stage approximately180 million years ago) period. Formed part of the ancient Tethys Ocean and the deposition of sediments creating the oil shales and the fossils therein which were deposited and fossilised in an anoxic (lacking in oxygen) deepwater environment. These shales contain rare fossil animals of the Jurassic period. Marine vertebrates, ichthyosaurs, plesiosaurs, ammonites (go to our ammonite pages) and crinoids ( review our crinoids pages). The Holzmaden (Posidonia shale deposits) are of worldwide importance because of the unique formation and the discovery of skin cover showing parts of fossilised fauna rarely seen in the palaeontological record. Only a few locations have such an environment which so finely preserved its fossil treasures. The Posidonia Shale fossils can be found at the Museum Hauff, Holzmaden, as well as museums around the world.

The presence of iron pyrite 'fools gold', in the Posidonia black ‘jet’ shales is an event created by the historic anoxic environment of the sea floor. Because the benthic level of the sea lacked a concentration of oxygen the biota of the oceans once deposited, post-mortem on the seafloor did not decay quickly, oxygen-loving bacteria did not form and decay the tissue of sea creatures like the Ammonites. Disc-like pyrite nodules indicate the anoxic environment of the Jurassic seas in this location. Low oxygen loving Algae formed in place of bacteria and produced sulphates which released hydrogen sulphates as a by-product. The further bacterial breakdown released sulphur which combined with iron minerals to form iron pyrite.

The Ammonites eventually becoming extinct in the Maastrichtian age, just before the mass KT extinction event. The Nautiloids survived probably due to their benthic ecology. Laying small batch eggs often, at depth or on the sea floor with more frequency, throughout their life, thus protecting the eggs from most significant climatic changes. Whereas the Ammonites laid one batch of numerous eggs at the end of life and attached these to marine planktonic environments, close to the surface which made them more susceptible to any significant planetary climatic change.