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Fossil teeth suggest shark diversity was unaffected by ancient extinction event

Researchers analyzed more than 1,000 fossil shark teeth to better understand how shark diversity was affected by the K-Pg extinction event. Photo by Benjamin Kear, Bazzi M et. al/PLOS Biology
Researchers analyzed more than 1,000 fossil shark teeth to better understand how shark diversity was affected by the K-Pg extinction event. Photo by Benjamin Kear, Bazzi M et. al/PLOS Biology

Aug. 10 (UPI) -- An analysis of ancient shark teeth suggests the marine predators were relatively unaffected by the extinction event that wiped out 75 percent of the planet's species, including the dinosaurs.

The Cretaceous-Paleogene extinction event, which most scientists now estimate was triggered by a massive asteroid impact, killed off not only the Earth's largest land-dwellers, but also massive marine reptiles like mosasaurs and plesiosaurs.

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According to a new paper, published Tuesday in the journal PLOS Biology, shark diversity began declining prior to the K-Pg extinction event and remained stable during and after the global catastrophe.

For the study, evolutionary biologists analyzed the morphology of 1,239 fossil shark teeth, remains spanning 27 million years and comprising species from eight existing orders and one extinct order.

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Though the fossils showed shark diversity as relatively constant during the mass extinction event, the marine predators weren't entirely immune. Scientists found evidence of isolated extinctions, particularly among predators with triangular blade-like teeth.

These selective predators may have died out following the disappearance of their preferred prey, researchers said.

Some shark groups increased their diversity in the wake of the K-Pg extinction.

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For example, members of the Odontaspididae family, a group of fish-eating sharks with narrow, cusped teeth, quickly diversified during the early Paleogene in response to rapid speciation among finned fish.

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The patterns observed among tooth morphology suggest sharks experienced an ecological transformation during the late Cretaceous and early Paleogene, with reptile-targeting specialists dying off and bony fish-eating generalists emerging.

"Ultimately, our study reveals a complex morphological response to the end-Cretaceous mass extinction and highlights an event that influenced the evolution of modern sharks," researchers wrote.

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