UK Ammonite Placenticeras
Placenticeras meeki
Pierre Formation
Upper Cretaceous (Campanian)
Meade County, South Dakota
This example of P. meeki has the original shell with some good red and green iridescence. The shell is thin in some areas and the underlying sutures are visible. The specimen is prepared on its original matrix and is a very good display. The ammonite is 8.5 inches across. There is a sliver of restoration along the venter (see illustrated photo). The innermost whorls are also restored. This mode of preservation is very typical for the locality.
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.