Ammonites were not in decline before they were wiped off by calamity that killed dinosaursScientists have discovered that ammonites, marine molluscs with iconic coiled shells were not in decline leading up to their extinction.
Illustration of marine ammonites basking under the late Cretaceous Sun.
Scientists had concluded that the ammonites were in decline even before the extinction by examining the fossil record, but the patterns of biodiversity in the fossil record can just reflect the patterns of sampling, rather than the actual biological history.
While the ammonites may have been struggling in North America, they were flourishing in other regions.
Corresponding author of the paper, Flannery Sutherland says, “Palaeontologists are frequently fans of silver bullet narratives for what drove changes in a group’s fossil diversity, but our work shows that things are not always so straightforward.
Ammonites were not in decline before they were wiped off by calamity that killed dinosaurs
Scientists have discovered that ammonites, marine molluscs with iconic coiled shells were not in decline leading up to their extinction.
Illustration of marine ammonites basking under the late Cretaceous Sun. (Image Credit: Artwork by Callum Pursall, @cpursall on X).
New Delhi: A team of researchers have challenged the prevailing notion that the demise of the ammonites was inevitable, and that ammonite diversity was decreasing long before the went extinct at the end of the Cretaceous, along with non-avian dinosaurs about 66 million years ago, an extinction event that was primarily driven by excessive volcanism. The marine molluscs with iconic coiled shells flourished in the oceans of the world for over 350 million years.
Scientists had concluded that the ammonites were in decline even before the extinction by examining the fossil record, but the patterns of biodiversity in the fossil record can just reflect the patterns of sampling, rather than the actual biological history. The blind spot for the scientists was that they were analysing the fossils that had been recovered as the complete global story of the ammonites, which pointed to a long-term ecological decline that was just not true.
The balance between speciation and extinction
The researchers assembled a new database of Late Cretaceous ammonite fossils to fill in the sampling gaps in the fossil record, drawing on collections from museums as against relying on published studies. The researchers discovered that the balance between evolution and speciation shifted through geological time and different geographic regions. While the ammonites may have been struggling in North America, they were flourishing in other regions. The diversity was not driven by a single factor, such as changing temperatures for example.
The stories told by fossils are complex and nuanced
A paper describing the findings has been published in Nature Communications. Corresponding author of the paper, Flannery Sutherland says, “Palaeontologists are frequently fans of silver bullet narratives for what drove changes in a group’s fossil diversity, but our work shows that things are not always so straightforward. We can’t necessarily trust global fossil datasets and need to analyse them at regional scales. This way we can capture a much more nuanced picture of how diversity changed across space and through time, which also shows how variation in the balance of Red Queen versus Court Jester effects shaped these changes.”
