7.3" Heteromorph Ammonite (Audouliceras) Fossil - Volga River, Russia

This is a very impressive heteromorph ammonite fossil of the genus/species Audouliceras matherioanum, quarried from the Volga River region of Russia. This specimen exhibits extensive opalescent mother-of-pearl along with diffuse pyritization. The ammonite itself is 7.3" wide, and has been professionally exposed from the rock. It is accompanied by a display stand.

There is some restoration on the ammonite, about 10-15% This is typical for most Audiloceras ammonites sold from this region.

Most ammonites are homomorphs meaning that they retain their spiral shell shape throughout growth. Heteromorph (different shaped) ammonites developed during the late jurassic and have uncoiled shells. It's hard to imagine how this shape would have given them an evolutionary advantage as it would have hindered fast movement.