The new analysis examines Neoselachii, the clade that contains modern sharks and rays, across a 145-million-year fossil record. The team compiled over 20,000 fossil entries and, using recent analytical methods, reconstructed the estimated times of origin and extinction for about 1,500 species. Their goal was to find pulses of diversification and loss and to explain those patterns.
The main finding is consistent and strong: species face a much higher extinction risk during their first four million years of existence than later on. This young-species vulnerability appears throughout the entire 145-million-year span and applies regardless of the cause of extinction. The study documents expected losses at the end-Cretaceous mass extinction, around 66 million years ago, and also reveals previously unknown events. One striking episode about 30 million years ago led to many extinctions but almost no subsequent rise in new species.
The data further suggest that over the past 40–50 million years too few new species have arisen to replace earlier losses. The authors therefore argue that species' age is a persistent predictor of extinction risk over evolutionary time. They add that modern sharks and rays are survivors of many past losses and gains, but they now face additional pressure from human activities. The paper appears in Proceedings of the Royal Society B, and the source is the University of Zurich.
Difficult words
- clade — group of related species with common ancestry
- fossil record — all fossils that show past life and history
- reconstruct — build an estimate of past events or datesreconstructed
- diversification — process when new species form and increase diversity
- extinction — end of a species when no individuals remain
- vulnerability — state of being especially likely to be harmed
- mass extinction — a global event causing many species to die
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- What consequences might follow if too few new species arise to replace earlier losses, especially for sharks and rays? Give reasons or examples.
- How could human activities increase pressure on sharks and rays, given the study’s finding about young-species vulnerability?
- Should conservation focus more on protecting young species or older, established species? Explain your view with reasons from the article.
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