UK Ammonite Placenticeras
Placenticeras meeki
Pierre Formation
Upper Cretaceous (Campanian)
Meade County, South Dakota
This example of P. meeki has the original shell removed to reveal the complex sutures of this fossil. The specimen is prepared on its original matrix and is a very good display. This specimen includes the counter-part with the impression and original shell material. It is a wonderful illustration of the mode of fossilization typical of ammonites found in the Pierre Shale. The ammonite is over 14 cm across. The innermost whorls in the umbilicus are restored.
Placenticeras meeki is distinguished by its smooth convex, broad, nearly unornamented flanks and smooth venter. Some specimens ocassionally possess small tubercles along the umbilical shoulder and some slight, broad, low ribbing. P. meeki has a large size range up to 80 cm in diameter. the narrow concave venter is the smaller specimens becomes more rounded in larger shells. The species is rare in the Exiteloceras jenneyi Zone and is abundant in the Didymoceras cheyennense through Baculites cuneatus Range Zones throughout marine Cretaceous deposits of the Western Interior.