The study focuses on Neoselachii, the group that includes modern sharks and rays. Using new methods, the team reconstructed the origin and extinction ages for roughly 1,500 species from more than 20,000 global fossil records dating back to the Cretaceous.
They found a striking pattern: species are far more likely to go extinct during the first four million years after they appear. This higher risk holds across the 145-million-year span and across different causes of extinction. For example, sharks and rays suffered high losses during the mass extinction at the end of the Cretaceous, about 66 million years ago.
The researchers also identified previously unknown extinction events. One loss around 30 million years ago caused many extinctions with little recovery. The authors conclude that species age is a persistent predictor of extinction risk, and they note that human pressures now add to these long-term risks.
Difficult words
- neoselachii — Group including modern sharks and rays.
- reconstruct — Find past events or dates from data.reconstructed
- extinction — End of a species; it no longer exists.extinctions
- fossil record — Collection of preserved remains or traces.fossil records
- cretaceous — A geologic time period long ago.
- persistent — Continuing for a long time without stopping.
- predictor — Something that shows the likely future outcome.
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Discussion questions
- Why might species be more likely to go extinct soon after they appear?
- How could identifying past extinction events help protect species today?
- Do you think human activities make extinction risk worse for sharks and rays? Why or why not?
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