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Douvilleiceras orbignyi (8)

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  • Product Code: F23651
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Description

Origin : Madagascar (Mahajanga Province)

Geological era : Early Cretaceous (Albian)

Age : 105 million of years


fossil ammonite, 58.2 gr, cm 4.8 x 2.5.

Douvilleiceras is an extinct cephalopod mollusc belonging to the Ammonites. He lived at the end of the Lower Cretaceous (Albian, about 105 million years ago) and his fossil remains were found all over the world, mainly in Europe and the Near East.
The shell of this ammonite was symmetrical, with a flat spiral, with a poor covering of the subsequent turns, of a vaguely globular appearance. The ornamentation consisted of simple but very robust coasts. These coasts brought more or less numerous tubercles that, in the animal alive, were surmounted by long thorns, sometimes partly preserved in the best preserved fossil specimens. The presence of the tubercles gives the lap section a typical polygonal pattern. The size of the shell, on average, was between 5 and 10 centimeters in diameter, although in some species it could exceed twenty centimeters in diameter in the most developed specimens.
At the beginning of development (up to about 2 cm in diameter) it had no ribs, with only two rows of tubercles; subsequently (up to about 7 cm of diameter) another tubercle appeared in a lateral position, and the coasts developed. The adult stage (over 7 cm in diameter) was multi-tuberculosis (distinguished by the appearance of new tubercles, more or less numerous depending on the species), while the senile (or gerontico) stage was characterized by the disappearance of the tubercles and by an ornamentation with simple ribs, which finally tended to disappear in the most long-lived specimens, with the last round almost smooth.
The suture line was of an ammonite type, relatively uncomplicated and jagged.
The broad profile of the coil offered considerable resistance to water: for this reason, and due to the presence of tubercles and thorns with a likely defensive function, it is thought that douvilleicerato was an inefficient swimmer. Probably it was a necto-bentonic form (that is a backdrop), a predator of small, not very mobile marine organisms.
Among the best-known species, it is worth mentioning Douvilleiceras mammillatum, of the Lower and Middle Albian.

The Ammonites are an extinct group of cephalopods, which appeared in the Lower Devonian about 400 million years ago and extinguished at the end of the Cretaceous, together with the dinosaurs (65 million years ago), leaving no known descendants. Like all cephalopods known this organisms were carnivorous: active predators of marine animals, microphagous (plankton), scavengers, and even cannibals. The shell of ammonites in general has the form of a spiral wound on a plan (although some species, such heteromorphy, have a more complex three-dimensional winding) and it is this feature that has given their name. The appearance infact resembles a coiled horn, like that of a ram (the Egyptian god Amon was commonly depicted as a man with ram's horns). Pliny the Elder described the fossils of these animals ammonis cornua, "horns of Ammon." Often the name of the species of Ammonites ends with -ceras, from a greek word (κέρας) whose meaning is, in fact, "horn" (eg. Pleuroceras etymologically means horn with the coast).
The shell was divided by septa into several rooms, including the clam occupied only the last. The others were used as "tubes" filled with gas and liquid to control the floating body. The ammonite could well change its depth in a manner similar to the current Nautilus.
Because of their extraordinary variability and distribution in marine sediments around the world the ammonites are considered fossils for excellence and guide-fossils of exceptional value, used for dating in stratigraphy of the sedimentary rocks.
The classification of ammonites is made on the basis of morphology and ornamentation of the shell, and the shape of septa, depending on the suture line.



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