Description
Origin : Northwestern Madagascar (Mahajanga)
Geological era : Late Jurassic (Oxfordian)
Age : 160 million of years
Size : 56,4 gr - mm 43 x 40 x 22
Ammonite Fossil Seashell mm 43 x 40 x 22 gr 56.4 Phylloceras heterophyllum Extinct Prehistoric Cephalopods Molluscs Mesozoic Cretaceous Collecting Paleontology Museum.
Also available in lots, at this link.
Pleasant fossil specimen of Ammonite from the Upper Jurassic from Madagascar, representative collectible find of good quality.
Specimen polished to highlight the character of ornamentation and the ammonitic suture lines of phylloid type (cells divided into elements more or less numerous leaf-shaped, high number of umbilical lobes and fractal geometry type).
The iridescent layer, with various colored reflections, in excellent condition, is perfectly visible. Only a piece, as in photos.
The Phyllocerate (Phylloceras) is a genus of cephalopod mollusc belonging to the Ammonoidea. It lived between the Lower Jurassic and the Lower Cretaceous (190-130 million years ago).
Phyllocerate was the most typical representative of the phylloceratines (Phylloceratina), a long-lived and fairly widespread suborder of ammonites, which 
developed in the Triassic and passed unscathed through the extinction that occurred between the Triassic and Jurassic.
This primitive ammonite had a high-profile shell with an oval, discoid-shaped spindle section. The navel was very narrow, while the ornamentation was practically absent or, at most, represented by simple, barely visible striations, which were interrupted in correspondence with the ventral region where the siphon was present. Some species had slightly wavy and uninterrupted ribs on the siphonal margin.
The suture, however, was extremely complex: narrow and elongated lobes and saddles gave rise to other lobes of smaller dimensions but with similar characteristics. The entire suture somehow resembled the fronds of plants (hence the name Phylloceras, which means “leaf-horn”). The animal's dwelling chamber occupied less than half of the last lap. The size of the shell could reach twenty centimeters in diameter, but was generally smaller.
The hydrodynamic profile of the shell, together with the rounded belly, suggests that the phyllocerate was a good swimmer, which could move at moderate speed by means of a propulsive jet.
The morphology of these animals developed very little during their evolution; it is assumed that the ancestors of Phylloceras can be found in the family of monophyllithids (Monophyllitidae), typically Triassic.
Among the best-known species, Phylloceras heterophyllum is worth mentioning. His remains have been found all over the world, particularly in Western Europe.
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 (κÎρας) 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 "air chambers" 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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