A new fossil-based study is reshaping how scientists understand extinction risk in sharks and rays, revealing that evolutionary youth – and not just environmental upheaval – plays a decisive role in which species survive over geological time.

Led by researchers at the University of Zurich (UZH), the international team analysed more than 20,000 fossil records spanning the last 145 million years. Their findings show that shark and ray species are most vulnerable to extinction within their first four million years of existence, while older species are significantly more resilient.

The results challenge a long-standing assumption that a species’ age has little bearing on its likelihood of extinction.

Using innovative analytical methods, the researchers reconstructed the origins and disappearances of around 1,500 shark and ray species (Neoselachii) dating back to the Cretaceous period.

“We were particularly interested in identifying when, over the past 145 million years, large numbers of new species emerged or disappeared, and how this can be explained,” said first author Kristína Kocáková of UZH’s Department of Paleontology.

The fossil record confirmed well-known losses during the mass extinction event that ended the age of dinosaurs around 66 million years ago. But the study also uncovered several previously unknown extinction events.

“We discovered other, previously unknown extinction events. However, many of these events, including the one at the end of the Cretaceous, were followed by the origination of new species”, explained Catalina Pimiento, UZH professor of paleobiology.

But what surprised the team most was that the more recent extinctions were not followed by the emergence of new species, including one around 30 million years ago.

“This one was far the most impactful, because many species went extinct but hardly any new species emerged afterward,” said Pimiento, the study’s senior author.

Across the entire 145-million-year timeline, one pattern remained strikingly consistent: younger species were far more likely to disappear than older ones, regardless of the cause. “If a species had existed for only about four million years, it was more vulnerable than one that had been around for 20 million years. The older species remained remarkably stable,” said Kocáková.

The findings place today’s sharks and rays in a deep evolutionary context. Modern species are the survivors of repeated cycles of loss and recovery – yet the data suggest that over the last 40 to 50 million years, new species have failed to emerge quickly enough to offset extinctions.

Crucially, the study shows that evolutionary age has remained a persistent predictor of extinction risk through deep time. “Modern sharks and rays have already lost much of their evolutionary potential and have now also come under pressure from humans. Understanding their past helps us recognise how important it is to protect the species that still exist today,” said Dr. Daniele Silvestro, a co-author of the study and one of the developers of the analytical methods used.

The research underscores the importance of conservation at a moment when many shark and ray populations are facing accelerating threats from overfishing, habitat loss and climate change – pressures that may further erode a lineage already shaped by millions of years of selective survival.

The full paper – ‘Global extinction events and persistent age-dependency in sharks and rays over the past 145 million years’ – is available to read now.

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