The Mystery of Survival: Why Did Nautiloids Outlive the Ammonites?
Key Details
- Ammonites, a highly diverse group of marine cephalopods, vanished 65.5 million years ago in the end-Cretaceous mass extinction.
- Nautiloids, a less diverse group of shelled cephalopods, survived that cataclysm and still exist today.
- Evolutionary biologist Michael Schmutzer and colleagues built the largest-ever dataset of Late Cretaceous shelled cephalopods, incorporating museum fossils and published data, to investigate the difference in survival.
New Findings Challenge Old Hypotheses
Previous hypotheses suggested that differences in geographic distribution could explain the survival gap. However, the new study found no support for this idea.
The researchers also reassessed the theory that larger egg size gave nautiloids an advantage. In a striking twist, they discovered that the few ammonite genera which briefly survived after the extinction had the smallest eggs.
"The findings indicate a need to revise the egg-size hypothesis," said Michael Schmutzer.
This suggests that ammonites and nautiloids may have employed fundamentally different survival strategies after the asteroid impact.
A Surprising Conclusion: Were Ammonites Just 'Unlucky'?
Schmutzer noted that the results point toward a different interpretation of the extinction event. Rather than being out-competed, ammonites may have simply been 'unlucky' in the chaotic aftermath of the disaster.
This is a remarkable conclusion for a group that had already existed for 350 million years and survived multiple mass extinctions, including the devastating Permian-Triassic event 252 million years ago.
Background & Presentation
The full study will be presented at the EGU General Assembly.
Text written by Megan Sever.