At the end of the Cretaceous Period, dinosaurs (besides birds) and many large marine reptiles suffered a cataclysmic end. Everyone knows about this mass extinction event, yet few consider the survivors of it. A new study has analyzed shark diversity before and after the mass die off.
Sharks are ancient creatures, and the oldest known form of vertebrate on the planet. Fossil records suggest that at one point in history, there were more than 3,000 types of sharks and their relatives. Sharks managed to survive during extinction events when the ocean lost its oxygen – including the die off during the Cretaceous period, when many other large species were wiped out.
Researchers from Uppsala University led by Mohamad Bazzi looked closely at the easiest shark remains to find – teeth. Examining the diversity of 1,239 fossil shark teeth, the team found that shark diversity had been declining before the extinction event.
The extinction, roughly 66 million years ago, happened at the boundary of the Cretaceous and Paleogene, the so-called K-Pg boundary. Even though shark diversity was diminished before the extinction, it stayed steady over the course of the event itself.
There were some exceptions to the overall rule – apex predator sharks with large triangular shaped teeth, did suffer some loss of species during the extinction. Possibly these extinctions were related to the extinction of prey species.
Other sharks, such as those from the family Odontaspididae, flourished after the K-Pg boundary and rapidly diversified. This family of sharks evolved narrow teeth for preying on fish.
The scientists speculate that the selective extinction in sharks may indicate an overall change in diet from more specialized predators to one of fish generalists. Ultimately, sharks proved to be more resilient in the face of extinction than most vertebrate groups.
The research is published in the journal PLOS Biology.