Excellent Heteromorph Ammonite Australioceras

Description: An excellent example of this classic Australian semi-enrolled ammonite. The specimen retains much of it’s calcite exoskeleton. Note the small nodes along both sides of the keel. Uncoiled ammonites are perhaps one of the most aesthetically pleasing of all cephalopods. This specimen stands gracefully up-right on it’s flat base.

While most ammonites have spiral shells that retain the same shape throughout growth (homomorph), the major group of Ancyloceratina, that appeared during the Late Jurassic had these uncoiled shells instead, and were called heteromorph ammonites (meaning, different-shaped).