Spectacular piece of ± 14 cms x 12 cms with ammonite (macroconcha) of ± 7.2 cm in diameter. The array is filled with small bivalve on both sides. It is not attached to the matrix, or restored.
"In the ammonites, macroconcha size of a given species (supposedly dimorphic female) could become up to 10 times larger than its corresponding microconch (dimorphic supposedly male).
Cretaceous Campanian supeior, Fox Hills Formation
Meade County, South Dakota (USA)