The asteroid that proved to be the coup de grâce to the non-avian dinosaurs almost finished off our own ancestral lineage too, according to new research. Writing in the Journal of Evolutionary Biology, a team of researchers note that up to 93 percent of mammal species also went extinct when the spacefaring apocalypse arrived on Earth.
By examining the published fossil record from western North America from 2 million years prior to the end-Cretaceous mass extinction event, to 300,000 years afterward, the researchers were able to ascertain roughly how many species evolved and compare it to how many became extinct. Although many previous studies assumed that mammals would have been affected by the asteroid impact, few would have predicted that they were almost completely wiped out by it.
“Because mammals did so well after the extinction, we have tended to assume that it didn't hit them as hard,” Nick Longrich, an evolutionary biologist at the University of Bath and the study’s lead author, said in a statement. “However our analysis shows that the mammals were hit harder than most groups of animals, such as lizards, turtles, crocodilians.”
Alphadon, a small mammal living during the Late Cretaceous, alongside the famous T. rex. MUSE - Science Museum of Trento; Wikimedia Commons; CC BY-SA 3.0
Despite this zoological hammering, the mammals then went on to take over Earth in much the way the dinosaurs did hundreds of millions of years earlier. It’s a remarkable thought that every single mammal alive today evolved from the 7 percent that made it through the asteroid impact, living alongside birds, who are of course dinosaurian descendants. The key to survival, it seems, was the ability of mammals to adapt.
When the asteroid hit, it conspired with massive, prolonged volcanism to significantly and rapidly alter the climate. The volcanism initially caused global cooling, before the massive carbon dioxide outflow warmed the planet. When the asteroid hit, it almost immediately darkened the skies, and the world cooled once more.
These low light levels and huge climatic fluctuations severely impacted vegetation’s ability to photosynthesize, and edible plants across the world died out. This killed off the herbivorous dinosaurs, which in turns sent shockwaves through the food chain. Many mammals, who at the time were often opportunistic omnivores – although some were large enough to eat dinosaurs – also died out this way.
Only the small survived, as they required the least amount of food to make it through the day. It’s likely they scavenged on dead plants and animals until life on Earth began to truly recover.
This adaptability proved to be a huge boon for the mammals: The team’s research suggested it only took them 300,000 years to recover from one of the worst mass extinction events in the history of the world. “It wasn't low extinction rates, but the ability to recover and adapt in the aftermath that led the mammals to take over,” Longrich added.
R. robustus, a mammal large enough to feed on small dinosaurs. Nobu Tamura/Wikimedia Commons; CC-BY 3.0
This research comes hot on the heels of another study, which revealed that the dinosaurs were in decline 50 million years before they officially bit the bullet; although no clear cause for this decline could be pinpointed, the researchers suspected the rise of opportunistic mammals, those that could steal dinosaurian resources, may have been to blame.
A second study also looked at how mammals suffered during the asteroid impact 66 million years ago, and it concluded that, indeed, many of them went extinct at the boundary. However, it also states that it took mammals several million years to recover from this event – a stark contrast to this new study, which suggests it was far more rapid.