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. This was not a gradual decline but a mass extinction triggered by a combination of severe environmental shocks.
Why Ammonites' Fossil Record Ends Abruptly: The Extinction Explained
The impact would have unleashed an energy release far beyond any human-made explosion, hurling vast amounts of debris into the atmosphere and causing immediate, catastrophic devastation at the impact site. This collapse of the base of the food chain would have devastated marine plankton, the primary food source for many small marine animals, which in turn were prey for larger creatures, including young and small ammonites.
Ammonites released vast numbers of tiny, free-floating larvae called "aptychi" into the water column. Their reliance on a healthy, sunlit ocean made them a canary in the coal mine, and they perished as the ecosystem they dominated collapsed.
Why Ammonites Fossil Record Ended Abruptly: Decoding the Extinction
Furthermore, their complex coiled shells, while hydrodynamically efficient and perhaps used for buoyancy control, may have been a liability in the chaotic aftermath of the impact. Why Ammonites Were Especially Vulnerable While the K-Pg event was a global catastrophe, the reasons ammonites were hit so much harder than their distant cousins, the nautilus, lie in their specific biology and life history.
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