Ammonite (microconch) perfect, pearly given by the fossilization of the shell with opalized reflexes.
Fossil of about ± 8 cm × ± 6.5 cms. The ammonite measures ± 4.7 cm in diameter.
"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 Fox Hills Formation
Meade CountySur Dakota (USA)