Researchers studied fossils that cover 145 million years. They used more than 20,000 fossil records and estimated ages for about 1,500 species of sharks and rays (Neoselachii).
The main result is clear: species are much more likely to go extinct within the first four million years after they appear. This pattern holds across the whole time period and happened during big events such as the mass extinction at the end of the Cretaceous, around 66 million years ago. The authors also report a big loss about 30 million years ago with little recovery afterward. Today, modern sharks and rays face extra pressure from humans.
Difficult words
- fossil record — collection of old animal and plant evidence in rockfossil records
- species — groups of animals or plants that are similar
- extinct — no longer living anywhere on Earth
- mass extinction — time when many species died quickly
- recovery — return to earlier numbers or health
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Discussion questions
- Why do you think young species may go extinct more often?
- What can people do to reduce pressure on modern sharks and rays?
- How do fossil records help scientists learn about the past?
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