The strangely weird looking heteromorph fossilised shell of this type of ancient mollusc is not so instantly recognisable as part of the sub orders of ammonoidea, ammonites. The eccentrically winding growth of the shell appears quite exotic. Up until quite recently its was thought that the evolving form was a period of decline during the Jurassic when this type of dimorphism first appeared in the fossil record of ammonoidea. For the ammonites the evolution of the heteromorph uncoiling whorls persisted up to their eventual extinction in the later Cretaceous period.
Now it established that in fact this was a radiation of types of heteromorphs which were developing and evolving a greater diversity rather than a declining last act of the ammonite group. This just so happened to be leading up to and at around the time of the great mass extinction at the KT boundary. The eccentric fossilised shell, termed an internal mould is from around 100 million years ago. Excavated from the High Atlas mountains of Morocco, the western province of Agadir-Ida Ou Tanane Prefecture and of the Souss-Massa, Marrakech-Safi region. The Fossil Store has surmounted the specimen fossil onto the superb bronzed mount, this balances the fossils securely, which can be lifted off the stand for transport and further study.
Early forms of Jurassic heteromorph ammonites had morphology which was not as exaggerated as this specimen, in their early development the last outer whorl of the shell became separate from the main inner spirals, this developed becoming more pronounced as in this example, eventually towards the end of the Cretaceous types were developing complex and convoluted intertwined types. A most fascinating glimpse back in time to a period of great expansion which finally and abruptly ceased.