This article was originally on Hakai magazine, an online publication about science and society in coastal ecosystems. Read more stories like this at hakaimagazine.com.
The ice age was kind to large mammals. From about 2.5 million to 11,700 years ago, they had the space – and the time – to roam far. Lions were once found all over the world. After evolving in East Africa, the big cats traversed Europe and Asia, eventually crossing into North America through Beringia, a now submerged continent that once connected Siberia to Alaska and the Yukon.
Lions roamed North America for tens of thousands of years before becoming extinct. Today, there are no lions lounging in southern Alberta’s rapeseed fields or chasing prey through the Yukon grasslands – so what happened?
Cave lions and their larger relatives, American lions, first entered North America during the last Ice Age, near the end of the Pleistocene. Already part of the landscape in Europe, people painted and carved portraits of these huge lions in caves, including the famous Chauvet Cave in France.
Cave art has provided scientists with information about what these lions may have looked like and how they lived, says Julie Meachen, a vertebrate paleontologist at Des Moines University in Iowa who specializes in big cats and other mammalian carnivores. The cave paintings show large manless lions with reddish coats living in groups.
Fossil evidence also indicates that, as with modern African lions, male Pleistocene lions were significantly larger than the females, Meachen explains. The maximum size of a male American lion was about 420 kilograms, she says, noting that modern lions weigh only 270 kilograms. “They probably could have killed just about anything they wanted to kill, except a fully grown one [male] mammoth,” she says.
Alexander Salis, a postdoctoral researcher in vertebrate zoology at the American Museum of Natural History in New York, took a closer look at the story of lions in North America as part of his research at the University of Adelaide in Australia. In collaboration with Meachen and a team of colleagues, Salis analyzed the mitochondrial DNA of 39 Pleistocene lions from North America and Eurasia. He determined that lions migrated to North America at least three times. But their adaptability faltered when faced with climate change and habitat change.
Each wave of lion migration seemed to correspond to changes in global climate and sea level, Salis explains. As the planet fluctuated between periods of freezing and melting, sea levels rose and fell, and Beringia was exposed and flooded many times. During ice ages, the expanding ice caused sea levels to drop, opening up the route to North America that lions took advantage of – each with DNA markers that revealed where they came from and when.
The first lions to enter North America about 165,000 years ago were a lineage of cave lions. When Beringia was flooded by a warmer period, the lions were cut off from Asian populations and evolved into the American lion, Salis explains. American lions didn’t spend much time in the north and instead made their way to what is now the United States, he says. Nearly all of the American lion remains have been found south of the ice sheets that once covered much of the continent, with the exception of a 67,000-year-old specimen from a Yukon site. Salis identified this as the oldest known American lion.
About 63,000 years ago, Salis says, a second wave of cave lions moved into eastern Beringia, now Alaska and Yukon. For some reason, these cave lions remained above the ice caps, separated from the American lions that had already spread south. Salis’s research found that this lineage of lions went extinct about 33,000 years ago.
That the extinction of cave lions in eastern Beringia can be attributed to a warming trend in the region, Salis says. The sea level rose and damp weather came, important ingredients for the growth of peat. The expansion of peat bogs in eastern Beringia would have fragmented habitats and altered vegetation, severely impacting herbivores and leaving cave lions and other carnivores in search of prey. The American lions that had spread south were unaffected.
Lions resurfaced in the fossil record of eastern Beringia about 22,000 years ago, when the last wave of cave lions arrived from Asia. But they had some bad luck.
At the end of the last ice age, temperatures rose and megafauna began to die out across the continent, aided by the presence of humans who quickly began to alter the environment. This one-two punch would have resulted in loss of vegetation and a decline in prey populations, which would have led to the demise of American lions and cave lions, Meachen says.
Andrew Cuff, a paleontologist and former lecturer at the University of Liverpool in England who was not involved in Salis’ research, says it makes sense that lions entered North America in multiple waves, taking advantage of the extra territory whenever Beringia was passable . He notes that many animals, including dinosaurs, used the route to move between continents.
Cuff adds that it’s nice when the data comes together like this to tell a cohesive story that also ties in with glacial, fossil and DNA records.
Lions weren’t the only cats to roam North America during the Pleistocene. Cougars (also known as panthers, cougars, and mountain lions) and several now-extinct species, including several saber-toothed cats, proliferated across the Americas long before the arrival of lions. North American cougars suffered the post-glacial extinction of megafauna, but South American populations survived, Meachen says. As deer and elk began to repopulate North America, the cougars returned.
North America was densely populated with an incredible diversity of species before the end of the Ice Age, Meachen says. By learning what has been lost, she hopes more people will understand the importance of biodiversity and the need to preserve it.
This article first appeared in Hakai Magazine and is republished here with permission.
