Which of the major mass extinction events most profoundly affected ammonites?

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BlackTom AI · Accepted Answer

To approach this question, let's review how ammonites fared across major extinction events and which event left the strongest imprint on their lineage.
Option a: End Permian. This was the most severe global extinction in Earth's history, wiping out a huge fraction of species across many groups. However, ammonoids did not disappear entirely at this boundary; they endured into the Early Triassic, albeit with evidence of significant turnover and reduced diversity. Thus, while impactful, the End Permian event did not eradicate ammonites nor leave as profound a selective stamp on them as the later event.
Option b: End Cretaceous. The End Cretaceous (K-Pg) boundary marks the mass extinction associated with the asteroid impact that killed the non-avian dinosaurs. Ammonites were driven to global extinction at this boundary, vanishing from the fossil record at the K-Pg event. This represents a major, decisive wipeout of their lineage, more so than in other mass extinctions, making it the event that most profoundly affected ammonites.
Option c: End Triassic. The End Triassic extinction opened ecological space and caused faunal turnover across many groups, but ammonoids persisted into the Early Jurassic and show a pattern of diversification after this boundary. Therefore, while it caused changes, it did not have the deepest and most lasting impact on ammonites overall.
Option d: End Ordovician. The End Ordovician extinction primarily affected marine invertebrates like graptolites and many shelled organisms in Ordovician seas. Ammonoids were not a dominant or defining group at this time (they are more characteristic of the Mesozoic), so this event is not the primary driver of ammonite history and would not be described as the most profound impact on them.
In summary, while multiple mass extinctions reshaped marine life, ammonites experienced a catastrophic, near-total extinction at the End Cretaceous boundary, whereas they persisted through or recovered from the others to varying degrees. This makes the End Cretaceous the event that most profoundly affected ammonites.

GEOL0003_24-25 Final Quiz (if you have a SORA use the alternative link below) (2025)

Which of the major mass extinction events most profoundly affected ammonites?

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