The incredible recovery of mammals in the aftermath of one of the most severe mass extinctions in Earth’s history.
After non-avian dinosaurs went extinct, mammals quickly started filling in niches that had been left vacant, and their diversity exploded.
"Because mammals did so well after the extinction, we have tended to assume that it didn't hit them as hard,” said Nick Longrich from the Milner Centre for Evolution at the University of Bath in a press release.
However, in a study published in the Journal of Evolutionary Biology, Longrich and his co-authors argue that mammals were in no way spared from the adverse effects of the mass extinction event that marked the end of the Cretaceous period.
The researchers reviewed the mammal fossil record in North America spanning two million years before the Cretaceous-Paleogene boundary all the way to 300,000 years after the asteroid hit. By comparing species diversity before and after the extinction event, they were able to estimate its impact on mammals and how quickly mammals recovered.
The fossil record revealed that more than 93 percent of mammal species went extinct along the Cretaceous-Paleogene boundary. This severity of extinction was much greater than previous estimates for mammals, which were potentially biased due to limited data sets.
"The species that are most vulnerable to extinction are the rare ones, and because they are rare, their fossils are less likely to be found,” Longrich explained. “The species that tend to survive are more common, so we tend to find them.”
By using bigger inventory of fossils in their analysis, the researchers were able to examine a greater number of rare species that died out. Longrich noted, “As bad as things looked before, including more data shows the extinction was more severe than previously believed.”
Yet the researchers also found that mammals recovered more rapidly than previously thought. In roughly 300,000 years — the blink of an eye in evolutionary terms — not only did mammals gain back their lost diversity, but they also doubled in number of species compared to their numbers prior to the extinction event.
“Our analysis shows that the mammals were hit harder than most groups of animals, such as lizards, turtles, crocodilians, but they proved to be far more adaptable in the aftermath,” Longrich said, noting that the study shows it wasn’t low extinction rates, but rather the ability to recover and adapt that led mammals to take over.