Phylloceras sp.
Jurassic
Tulear, Morandava
Madagascar
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This is an example of the ammonite Phylloceras that has been cut in a bilateral cross section to display the preserved internal chamber structure. Some of the chambers are filled with limestone and others with crystalline calcite. The exterior of the ammonite has been sanded and polished to show the suture pattern.
Phylloceras is an extinct genus of ammonoid cephalopods belonging to the family Phylloceratidae. These nektonic carnivores lived from Early Jurassic (Hettangian age) to Late Cretaceous (Maastrichtian age). Shells of Phylloceras can reach a diameter of about 8�10 centimeters(3.1�3.9 in), with a maximun of about 20 centimeters (7.9 in). These primitive ammonites had an involute, laterally flattened shell with a regular shell opening. They were almost smooth and the ornamentation was virtually absent or, at most, represented by simple growth lines barely visible. The striking sinuous suture lines were characteristic of this genus. They are reminiscent, in some ways, of the leaves of plants (hence the name Phylloceras, which means leaf-horn).