Elizabeth Sibert is rewriting the story of how the asteroid impact that killed off the dinosaurs affected fish, and she’s doing it one tooth at a time.
Based on close examination of thousands of fossilized fish teeth, Sibert, a Junior Fellow of the Harvard Society of Fellows, found that while the impact did cause some fish species to die off, it also set the stage for two periods of rapid evolution among marine life.
Of the 48 types of fish teeth that were found before the extinction, Sibert and colleagues discovered that just two were wiped out, an extinction rate far below that experienced by other creatures during the same period. Those two, however, were the dominant species, as they made up nearly half of all teeth found before the extinction, so in their absence other types quickly evolved to fill that void.
“I think fish are one of the ultimate survivors,” Sibert said. “And I say that because every time we make a prediction about what fish are going to do at a time of major global change, be it rapid global climate change or mass extinction, we’ve been wrong in some way.
“So 66 million years ago, when an asteroid hit the planet, it blocked out the sun for several months, which turned off photosynthesis, causing the food web to collapse,” Sibert said. “That meant a lot of things died because they didn’t have any food. What we found was that some of the major fish species, two out of 48, went extinct … but then something clearly happens because we see these two radiations [of new tooth types].”
To understand how the extinction event impacted fish, Sibert had to get her hands dirty — literally.