Ammonite Madagascar (Goat Horn Douvilleiceras mammillatum +Cleoniceras)

Ammonite (Goat Horn) Douvilleiceras mammillatum 125 mya to 109 mya from Madagascar The intricate suturing pattern provided strength to the ammonite. The linear structure evident at the midline is the siphuncule, an integral part of the ammonite’s “ballast system”. The ammonite moved freely at depth by pumping water in an out by means of the siphuncule. Ammonites were predatory cephalopod mollusks that resembled squids with spiral shells. They are more closely related to living octopuses, though their shells resemble that of nautilus species.

True ammonites appeared in the fossil record about 240 million years ago during the Triassic Period, descending from straight shelled cephalopods (baculites). The last lineages disappeared 65 million years ago at the end of the Cretaceous. Many Ammonites floated or swam above seafloors that lacked oxygen to support animal communities. When they died, they drifted to the bottom and bacterial decomposition altered the redox chemistry of the water- making minerals less soluble and thereby concreting around the ammonite. This scenario promoted excellent preservation of shell material.

Though soft tissues are poorly preserved, some ink sacs and beak-like jaws have been found. The rapid evolution of distinguished genera, their subsequent extinction after a few million years, and the excellent preservation of unique shell features make ammonites an excellent index fossil. Ammonites grew by adding new and bigger chambers. The largest ammonite that has been discovered was 8. 5ft in diameter!

The squid-like part of the animal (soft-body) lived inside the last chamber which was also the biggest. In females, the chambers also contained the eggs. The coil of the ammonite shell has often been sought after for its Feng Shui properties. The spiral also follows the Fibonacci sequence which is endless. Therefore, the symbol of infinity is associated with ammonites.

Some fossils have beautifully preserved coils at their centre while others may not show any sign of a coil. There are also two different reoccurring types of coils; an outward coil and the common inward coil. Fossils that display a spiral will be more highly valued than one that does not. Ammonite (Cleoniceras) Fossil - Madagascar