An artist’s impression of Diplomoceras maximum
An ancient squid-like animal with a shell that looked like a 1.5-metre-long paperclip may have typically lived for 200 years.
Diplomoceras maximum lived about 68 million years ago, making it a contemporary of Tyrannosaurus rex. It was an ammonite – a now-extinct group of tentacled cephalopods – and it had a distinctive paperclip-shaped shell.
“It’s hard not to be entranced,” says Linda Ivany at Syracuse University, New York. “It’s as tall as I am.”
D. maximum’s unusual shell shape makes it difficult to unravel its biology, but Ivany and her colleague, Emily Artruc, have now uncovered hints that individuals might have had very long lives. The evidence comes from chemical signatures locked away in samples taken at regular intervals along a 50-centimetre-long section of D. maximum shell.
When she and Artruc examined the carbon and oxygen isotopes along the shell, they found a repeating pattern in the isotopic signatures that they suspect reflects the annual release of methane from the sea floor. This annual pattern matched up with the sculptural ridges, or ribs, perpendicular to the length of the shell. This suggests that D. maximum added one new rib to its shell each year. “These shells grow by accretion, adding a new increment annually,” says Ivany.
Given that a 1.5-metre-long shell contains many dozen ribs, that leads to an obvious conclusion. “The only scenario that seems to work is to make this thing 200 years old,” says Ivany, who presented the research at an online meeting of the Geological Society of America last week.
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. “These are not centenarians,” says Ivany.
Why D. maximum might have had such a long lifespan isn’t clear. It lived around Antarctica, where food must have been difficult to come by during the long and dark winter. 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.
Either way, the new evidence for the length of the lifespan will lead to a deeper understanding of the living paperclip’s lifestyle, says Ivany. “If you know something about an organism’s lifespan, you learn a lot about its ecology.”