For years, scientists thought ammonites, the spiral-shelled creatures of the sea, vanished when the dinosaurs did, about 66 million years ago. But a fresh study in Scientific Reports shows some survived much longer, causing researchers to wonder what finally led to their end.
Ammonites were incredibly successful. They thrived in Earth’s oceans for over 340 million years, navigating three major mass extinctions before the Cretaceous–Paleogene (K–Pg) event. Their beautifully coiled fossils can be found around the globe, from the cliffs of Morocco to England’s Jurassic Coast.
Traditionally, it was thought that ammonites became extinct right after the asteroid impact due to rapid ocean changes and food chain collapse. However, recent fossil discoveries challenge this idea.
The new evidence is from Stevns Klint in Denmark, a UNESCO World Heritage site known for preserving fossils from both before and after the extinction. In a recent paper, Professor Marcin Machalski and his team found ten ammonite fossils in limestone layers dating from the early Paleogene—long after the asteroid hit.
These fossils belonged to three known groups: Hoploscaphites, Baculites, and Fresvillia. Most of these fossils were found in their original layers, suggesting they had survived the initial catastrophe for up to 200,000 years longer than previously believed.
If ammonites didn’t die right away, what led to their eventual extinction? The concept of “Dead Clade Walking” might hold the answer. This term describes species that endure an extinction event but fail to thrive afterward due to ongoing stresses.
Even though the ocean likely stabilized within tens of thousands of years, its ecosystems remained disrupted. Ammonites, particularly those that fed on plankton, may have struggled for food. Their genetic diversity and ecological resilience might not have been enough for a full recovery.
Interestingly, their relatives, the nautiloids, survived. Nautiloids lived deeper in the ocean and had slower reproductive cycles, giving them advantages in the unstable post-impact environment.
The long-held belief of ammonite extinction alongside the dinosaurs persisted partly because Paleogene ammonite fossils are rare. Many were considered older fossils shifted by geological activity. The well-preserved fossils found at Stevns Klint present a significant challenge to this view, revealing that our understanding of extinction events can be misleading.
This discovery emphasizes how new evidence can reshape scientific narratives. Even established timelines can drastically change with fresh facts, reminding us that nature still holds many surprises. Understanding these creatures helps us not only see the past but also learn more about survival in changing ecosystems.
For further details on this groundbreaking research, check the full article in Scientific Reports.
