Ammonites Were Thriving Before the Catastrophe That Killed the Dinosaurs

Ammonites, the marine molluscs known for their spiral shells, were not in decline before the catastrophic event that wiped out the dinosaurs, scientists have found.

An illustration shows marine ammonites basking under the late Cretaceous Sun. (Image Credit: Artwork by Callum Pursall, @cpursall on X).

New Delhi: A group of researchers has challenged the common belief that ammonites were already on the path to extinction before the end of the Cretaceous period, around 66 million years ago. This extinction event, which also killed off non-avian dinosaurs, was mainly caused by massive volcanic activity. Ammonites had thrived in the world’s oceans for over 350 million years.

Previous studies suggested that ammonites were declining before their extinction by looking at the fossil record. However, these patterns might just reflect how fossils were collected rather than the true history of these creatures. Scientists had a blind spot because they were treating the fossils they had as the complete story of ammonites, which led to the incorrect conclusion of a long-term decline.

Balancing Evolution and Extinction

To address this, researchers created a new database of Late Cretaceous ammonite fossils, using museum collections instead of just published studies. They found that the balance between evolution and extinction varied over time and across different regions. While ammonites might have been struggling in North America, they were thriving in other parts of the world. Their diversity wasn’t driven by a single factor like changing temperatures.

Complex and Detailed Fossil Stories

The findings have been published in the journal Nature Communications. Flannery Sutherland, the lead author of the paper, explained, “Palaeontologists often like simple explanations for changes in fossil diversity, but our research shows it’s not that simple. We can’t always trust global fossil datasets and need to look at them on a regional level. This way, we get a more detailed picture of how diversity changed over time and space, showing how different factors influenced these changes.”