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Ammonites' extinction was complex, not inevitable

When you think of extinction and extinct creatures, dinosaurs and ammonites are likely the first that come to mind.

These marine creatures, whose existence spans over 350 million years, became extinct around 66 million years ago, intriguing scientists and fossil fanatics alike.

The prevailing narrative amongst palaeontologists has been that the extinction of ammonites was inevitable due to their decreasing diversity.

Yet a game-changing study recently published in a renowned scientific journal begs to differ.

Decoding the extinction of ammonites

Led by a group of palaeontologists from the University of Bristol, the research unraveled the complexity of the last chapter of the ammonite evolutionary history.

“Understanding how and why biodiversity has changed through time is very challenging. The fossil record tells us some of the story, but it is often an unreliable narrator,” stated Dr. Joseph Flannery-Sutherland, the lead author of the study.

By simply analyzing the Late Cretaceous ammonite fossil record, previous researchers were led to believe the ammonites were in a long-term ecological decline. However, this team took an audaciously different approach.

Filling in the gaps of the record

Understanding the need for a more thorough assessment, the team created a new database of Late Cretaceous ammonite fossils, drawing from diverse museum collections.

Study co-author Cameron Crossan, a graduate of a prestigious palaeobiology program, noted that the strategy was to “provide new sources of specimens rather than just relying on what had already been published.”

This expansive new approach allowed for a more accurate depiction of ammonite biodiversity prior to their extinction.

Upon an in-depth analysis of their database, the team discovered a surprising trend: the balances of speciation and extinction of ammonites weren’t consistent – they varied across different regions and geological times.

“Their fossil record in parts of North America is very well sampled, but if you looked at this alone, then you might think that they were struggling, while they were actually flourishing in other regions. Their extinction really was a chance event and not an inevitable outcome,” explained Dr. James Witts, a senior researcher from the Natural History Museum, London.

Factors contributing to ammonite success

Exploring what drove the continued success of ammonites during the Late Cretaceous, the team identified multiple potential factors.

They considered if the speciation and extinction of ammonites were primarily due to environmental conditions (the Court Jester Hypothesis) or biological processes (the Red Queen Hypothesis).

As per the findings, the causes of these phenomena were tied to geographical differences.

“You couldn’t just look at their total fossil record and say that their diversity was driven entirely by changing temperature, for example,” said study co-author Dr. Corinne Myers of the University of New Mexico.

Complex reality of ammonite extinction

The new research has shed light on the more complex reality of ammonite history.

“We can’t necessarily trust global fossil datasets and need to analyze them at regional scales,” concluded Dr. Flannery Sutherland.

The story of ammonites’ extinction is indeed a complex tale of varied environmental conditions, geographical diversities, and consistent evolution.

Legacy of ammonites in modern science

Ammonites continue to leave an indelible mark on contemporary science. Their well-preserved fossils provide crucial chronological markers, aiding geologists in dating rock layers and correlating geological events across different regions.

Dubbed “index fossils,” these remnants are invaluable in reconstructing ancient environments, offering a window into Earth’s evolutionary narrative.

Furthermore, the intricate patterns on ammonite shells, reminiscent of nature’s very own art, serve as a source of inspiration in the study of mathematical models and biological processes.

The echo of their existence isn’t confined to history – it’s a cornerstone for ongoing scientific exploration and understanding. Perhaps, in studying these ancient mariners, we might find not just answers about the past, but keys to navigating the future.

Moreover, the evolutionary adaptations observed in ammonites – such as variations in shell shape, size, and ornamentation – offer insights into the mechanisms of natural selection and speciation.

Delving into these ancient organisms not only enriches our understanding of evolutionary biology but also sharpens our tools for scientific investigation.

The study is published in the journal Nature Communications.


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