Heteromorph Ammonite Labeceras

Description: An excellent example of this classic Australian uncoiled (heteromorph) ammonite. The specimen retains much of it’s calcite exoskeleton. The smaller specimen appears to be a semi-enrolled Australioceras jackii. Note the small nodes along both sides of the keel. Such ammonites are perhaps one of the most aesthetically pleasing of all cephalopods.

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).