Fish teeth show winners of massive die-off

"Fish teeth are tough, so they get preserved and give you the potential to put together the history of fish for hundreds of millions of years," says Pincelli Hull. (Credit: Mike Beauregard/Flickr)

An analysis of ancient teeth and shark scales suggests that fish populations in the Pacific Ocean were largely unaffected by a mass extinction event 66 million years ago.

Known as the Cretaceous-Palaeogene extinction, the event at the end of the Cretaceous period killed off roughly three-quarters of the animal and plant species on the planet.

In Earth’s oceans, the extinction of phytoplankton created a ripple effect that ravaged prey and predator species throughout the food chain.

“The Pacific just looks different during this period,” says Pincelli Hull, a Yale University assistant professor of paleontology and one of the authors of the study published in the journal Nature Geoscience. “From an ecosystem perspective, the Pacific appeared to be relatively unaffected.”

Paleontologists have become increasingly interested in studying mass extinction events.

“They give us case studies for understanding how species and ecosystems respond to change,” Hull explained. “We have a lot of gaps in our understanding of how the world functions during and after extinctions.”

Thousands of teeth

One way to fill in those gaps is to study fish teeth, which sit on the bottom of the world’s oceans in piles of marine fossils many football fields deep. For decades, scientists have been collecting deep-sea samples that contain thousands of teeth during open-ocean drilling expeditions.

“Fish teeth are tough, so they get preserved and give you the potential to put together the history of fish for hundreds of millions of years,” Hull says.

For this study, researchers compared tooth samples from the Pacific with samples from the Tethys Sea, an ancient seaway that lies partly where the Mediterranean is today.

In the Tethys, they discovered, fish populations fell sharply during the Cretaceous-Palaeogene event and remained depressed for at least 3 million years. In the Pacific, fish abundance held steady or increased for at least 4 million years—despite significant extinctions in the region.

Thus far, scientists have no solid explanation for the difference. However, the findings point to the likelihood of great variability and complexity within regional ecosystems after large-scale extinction events.

“It is the difference between biodiversity itself, and what biodiversity can do,” Hull says. “It’s a message of hope and a message of complexity.”

Researchers from the Scripps Institute of Oceanography at the University of California, San Diego contributed to the research.

Source: Yale University