Age: 217-212 million years old
Period: Late Triassic
Field notes: Maximum diameter 120 mm. From the Kiritehere coast, west of Waitomo, North Island, New Zealand. Ammonites (extinct) were squid-like animals (and distant relatives of squid and octopi) that lived inside a coiled shell. Their shells are divided into chambers by complexly folded partitions (called septa). In the close-up photo you can see just how complexly folded these septa could be. Compare them with the simpler chamber pattern of the closely related Goniatite Cymaclymenia. Why did they have chambers? With chambered shells Ammonites behaved like submarines, they could pump gas or liquid into or out of the chambers to change their buoyancy and because of this feature they were easily able to rise up into shallow water at night to feed and sink down in the ocean depths during the day to escape predators such as fish and Ichthyosaurs. Living squid do the same day/night migration. The complexly shaped chambers mean they could also make a light but very strong shell to survive the crushing pressures of the deep ocean.