The ammonites' specialization and intricate life cycle, which was finely tuned for the stable and productive Cretaceous seas, left them ill-prepared for the sudden, multi-front assault of the K-Pg event. Without a stable supply of food, populations would have crashed rapidly.
Why Ammonites Were Outcompeted by the Survivors
The most widely accepted cause is the impact of a massive asteroid or comet, approximately 10 to 15 kilometers in diameter, which struck the Earth near what is now the Yucatán Peninsula in Mexico. Ammonites, which relied on building and maintaining their intricate calcium carbonate shells, would have been exceptionally vulnerable to this acidification.
The nautilus, a distant relative that also survived the extinction event, has a simpler, more robust shell and a different reproductive strategy, releasing fewer, larger offspring that are better equipped to survive harsh conditions. The initial blast wave and global wildfires would have been followed by a prolonged period of "impact winter.
Why Ammonites Were Outcompeted by Hardier Survivors
Their reign began in the Devonian period and lasted through the Jurassic and Cretaceous, creating a fossil record so rich they became iconic markers for geological time. These larvae were essentially planktonic, drifting with the currents and forming a crucial part of the marine plankton community.
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