A Professor of Evolutionary Paleoecology and Paleoclimate at Syracuse University, Scientist Linda Ivany in upstate New York studied the remains of a now-extinct Diplomoceras maximum, an amazing ammonoid. This pre-historic cephalopod-like being lived about 68 million years ago. The animal was similar to squid but had a very unique shell that bent into itself over and over just like a paper clip, as the ammonoid grows older. Ivany determined that these underwater creatures lived for astonishing 200 years. The lifespan of modern cephalopods is very short.
At first glance, a 200-year-old shellfish might seem unremarkable, given that some modern shellfish can live more than twice as long. But D. maximum was a cephalopod, and all modern cephalopods live fast and die young. Octopuses and squid – even the gigantic forms – live no more than about 5 years. Nautilus, shelled cephalopods, can survive into their twenties.
The exception is probably the temperature of the water and very slow metabolism. The Diplomoceras maximum was supposed to live in the waters off of Antarctica, which gave a very harsh environment.
Ivany speculates that the ammonite might have had a slow metabolism to cope, and lived a long life as a side effect. Alternatively, a long lifespan might have been an adaptation to maximise the chances of reproducing successfully in such a challenging environment.