Large Polished Perisphinctes Ammonite From Madagascar
Lower Jurassic Period- C. 165-160 Million Years Ago
Order to which the fossil belongs: Ammonitida
Name of which the family belongs: Perisphinctidae
Informal name of the fossil: Ammonite
Members of the Perisphincidae are characterized by open, evolute shell forms, with rounded whorl sections and ornamentation of branching ribs. The suture is complex and has a long living chamber which occupies nearly a whole whorl of the shell. The typical diameter of the Perisphinctes is 4cm.
Ammonites are a form of ammonoid which are distinguished by their complex suture lines. They evolved very rapidly to produce numerous species and genera, but it was during the Late Cretaceous period that the ammonites and other marine groups, like belemnites, and terrestrial groups, like dinosaurs became extinct.
The name ammonite, was inspired by the spiral shape of their fossilized shells, resembling tightly coiled rams’ horns. Many ammonoids probably lived in the open water rather than at the sea bottom, this is due to the fact that their fossils are often found in rocks that were laid down under conditions where no bottom-dwelling life is found. They are typically evolute with the inner whorls exposed, but some are commonly stout and more involute and strongly ribbed with pronounced tubercles.
A nice example of a polished Ammonite with a nice iridescence.
Size: 88mm x 110mm approx