This article was originally featured 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 11,7srcsrc years ago, they had the space—and the time—to roam far. Lions, for instance, were once found around the world. After evolving in eastern Africa, the big cats padded through Europe and Asia and eventually crossed into North America by way of Beringia, a now-sunken continent that once connected Siberia to Alaska and Yukon.
Lions prowled North America for tens of thousands of years before going extinct. Today, no lions lounge in southern Alberta canola fields or chase prey through Yukon grasslands—so what happened?
Cave lions and their larger relatives, American lions, first entered North America during the last ice age, toward the end of the Pleistocene. Already part of the landscape in Europe, humans painted and carved portraits of these enormous lions in caves, including the famed 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 Iowa’s Des Moines University who specializes in big cats and other mammalian carnivores. The cave paintings depict big maneless 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 42src kilograms, she says, noting that modern lions only get up to 27src kilograms. “They probably would have been able to kill just about anything they wanted to kill—minus a fully grown [male] mammoth,” she says.
Alexander Salis, a vertebrate zoology postdoctoral researcher 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 into North America on at least three separate occasions. But their adaptability faltered when faced with climate 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 glacial periods, expanding ice caused sea levels to drop, opening the route into North America, which lions took advantage of—each bringing DNA markers revealing where they came from and when.
The first lions to amble into North America around 165,srcsrcsrc years ago were a lineage of cave lions. When a warmer period led Beringia to flood, the lions were cut off from Asian populations, and they evolved into the American lion, Salis explains. American lions didn’t spend much time in the north and instead headed for what is now the United States, he says. Nearly all American lion remains have been found south of the ice sheets that once covered much of the continent—save for one 67,srcsrcsrc-year-old specimen from a Yukon site. Salis identified this as the oldest-known American lion.
About 63,srcsrcsrc years ago, Salis says, a second wave of cave lions crossed into eastern Beringia—now Alaska and Yukon. For some reason, these cave lions stayed above the ice sheets, remaining separate from American lions that had already dispersed south. Salis’s research revealed that this lion lineage went extinct around 33,srcsrcsrc years ago.
That extinction of cave lions in eastern Beringia could be attributed to a warming trend in the region, Salis says. Sea levels rose and damp weather arrived, key ingredients for the growth of peat. The expansion of peatlands in eastern Beringia would have fragmented habitats and altered the vegetation, heavily impacting herbivores and leaving cave lions and other carnivores scrambling to find prey. The American lions that had spread south were unaffected.
Lions reappeared in eastern Beringia’s fossil record about 22,srcsrcsrc years ago when the final wave of cave lions arrived from Asia. But they ran into some bad luck.
At the end of the last ice age, the temperature rose and megafauna across the continent began to die out, helped along by the presence of humans who quickly began to alter the environment. This one-two punch would have triggered vegetation loss and a drop in prey populations, leading to the demise of American 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’s research, says it makes sense that lions entered North America in multiple waves, taking advantage of the extra territory each time 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 coherent story that also aligns with glacial, fossil, and DNA records.
Lions weren’t the only cats roaming North America during the Pleistocene. Cougars (also known as panthers, pumas, and mountain lions) and several now-extinct species, including various saber-toothed cats, radiated across the Americas long before lions arrived. North American cougars were a casualty of the post–Ice Age megafauna extinction, but South American populations survived, Meachen says. Once deer and elk began to repopulate North America, cougars returned.
North America was densely populated by an incredible diversity of species before the end of the Ice Age, Meachen says. In learning what has been lost, she hopes more people come to understand the importance of biodiversity and the need to preserve it.
This article first appeared in Hakai Magazine and is republished here with permission.