As many as 63 percent of the mammals living in Africa and the Arabian Peninsula became extinct. But we’re just now finding out.

About thirty million years ago, the Earth’s climate changed completely. Unlike today, our planet became cooler, the ice caps expanded, sea levels dropped and lush forests gave way to vast grasslands. Although this is known to herald the demise of two-thirds of the species living in Europe and Asia at the time, African mammals managed to escape the dance. At least… that’s what we thought.

African mammals

Until recently, African mammals were believed to have emerged relatively unscathed. The mild African climate and proximity to the equator would have acted as a buffer, protecting the area from the worst of the cooling. But now, thanks in large part to a large collection of fossils found in the burning Egyptian desert, researchers have shown that African mammals – despite their ‘pleasant’ environment – ​​were hit just as hard as the species found in Europe and Asia.

fossils

The team studied hundreds of fossils belonging to five mammalian groups, which enabled them to build evolutionary family trees. This allowed them to accurately determine when new lineages branched and to time-stamped the first and last appearances of each species. It leads to an interesting conclusion. For the findings show that all five mammalian groups suffered enormous losses in the transition from the Eocene geological period to the Oligocene; about thirty million years ago. “It really was a reset button,” said researcher Dorien de Vries.

Some of the fossils examined. Left: the primates, top right: the carnivorous hyaenodon, bottom right: rodent. Image: Matt Borths

It means that the mammals that roamed the African continent are far from thriving in the new, cold environment. And that means that the thirty-million-year-old mass extinction was a lot more massive than thought. As many as 63 percent of the mammals living in Africa and the Arabian Peninsula became extinct.

Challenges
The few surviving species did not have it easy. As temperatures dropped, East Africa was also ravaged by a series of disastrous geological events, such as volcanic eruptions and flood basalts – massive eruptions that covered vast areas with molten rock. At the same time, the Arabian Peninsula separated from East Africa, creating the Red Sea and the Gulf of Aden.

While this may seem like a pretty fateful ending, surprisingly, these groups reappear in the fossil record after a few million years. Although they have undergone a transformation. For example, the rodents and primates that reappeared had different teeth. They were new species, eating different foods and making other habitats their home. “It’s very clear that a recovery period followed the mass extinction,” said researcher Steven Heritage. And that also makes extinctions quite interesting. “It kills, but it also opens up new ecological opportunities for the genera that survived in the new world,” said study researcher Matt Borths.

Man

It means that the thirty-million-year-old mass extinction represents a particular evolutionary bottleneck. Although most genera became extinct, a few managed to survive. And over the following millions of years, these remaining lines diversified. Our own ape-like ancestors also almost completely disappeared from the face of the earth. Almost. Because a few managed to survive. “If they had died out 30 million years ago, we might never have been there,” said researcher Erik Seiffert. “Fortunately, that didn’t happen.”

The study reveals that much diversity has been lost on the Eocene-Oligocene boundary. More than was previously thought. But the species that survived apparently had enough to cope with the fluctuating climate. “Climate changes over geological time have shaped the evolutionary tree of life,” said researcher Heshem Sallam. “Gathering evidence from the past is therefore a great way to learn how climate change affects ecological systems.”