Ancient fires drove large mammals extinct, a new study suggests
Friday, August 18th, 2023
Wildfires spurred by human activity caused disappearance of sabertooth cats, dire wolves and other large North American mammals, suggest fossils from La Brea Tar Pits in Southern California.
Wildfires are getting harsher. Frequency of wildfires has gone up three times compared to 20 years ago in some parts of United States, say scientists. Scientists also say that expanse of such wildfires is up to four times compared to wildfires experienced 20 years ago. Smoke from Canadian blazes this summer turned North American skies an unearthly orange. “Fire whirls” were sighted in the Mojave Desert and raging flames proved disastrous for Maui.
Studying records of the distant past lead us to reasons that drove increased fire activity in bygone ages and results of such increased fire activity. In a fresh study published on 16th august 2023 in the journal Science, a group of palaeontologists that examined and analysed fossil records at La Brea Tar Pits, a famous Southern California excavation site, drew conclusion that dire wolves, sabertooth cats and other large mammals in this region disappeared nearly 13,000 years ago due to rising temperatures and increased fire activity spurred by people.
“We implicate humans as being the primary cause of the tipping point,” said a Marshall University evolutionary biologist Robin O’Keefe. O’Keefe added, “What happened in La Brea, is it happening now? Well, that’s a really good question — and I think we should figure it out.”
Earth has gone through five mass extinction events so far; some scientists claim that the disappearance of large mammals at the end of the last ice age was the beginning of a sixth. “It was the biggest extinction event since an asteroid slammed into Earth and wiped out all the dinosaurs,” opined a paleoecologist at La Brea Tar Pits and Museum and author of the new study, Emily Lindsey. Emily’s opinion is that the said disappearance was “the first pulse” of sixth mass extinction.
As yet, researchers have been unable to pin down exactly what caused these animals to go extinct. La Brea Tar Pits is one of the very few sites on the earth with fossil record large enough for scientists to investigate the question. Still active pits spread across 13 acres of land, are covered with bubbling black asphalt that has seeped to the surface from inside Earth. Prehistoric animals that got stuck in this goo died due to fatigue or predation, and their remains got preserved and fossilized by the asphalt. “And that’s still happening today,” Dr. O’Keefe informed. “You can go out to La Brea and see a squirrel stuck in the tar — I’ve seen it with my own eyes.” That’s hard luck for the animals, but good fortune for scientists: La Brea now boasts of a continuous unbroken fossil record of the region stretching as far back as 55,000 years.
Dr. O’Keefe and his team studied fossils for eight large mammal species — including the sabertooth cat, Camelops hesternus, an ancient camel and the American lion — that lived between 10,000 and 15,600 years ago. The team found out that seven of these species went extinct around 13,000 years ago, relying on radiocarbon dating. To understand why, the researchers analysed climate, pollen and fire records in the region in conjunction with continental human population growth at the time. They discovered that human occupation began to rise briskly around the same time that Southern California entered a period of severe drought and warming. Extreme fires followed, and the vegetation, once rich in oak and juniper trees, was ultimately replaced by grass and chaparral shrubs. “What we see is that you have a 400-year-long period of massively elevated wildfire,” said a paleobotanist at La Brea Tar Pits and Museum and an author of the new paper, Regan Dunn. Regan added, “And at the end of that period, you’re in a different ecosystem and all of the megafauna are gone.”
Dr. O’Keefe termed the conditions as the perfect storm: “You have a bunch of different factors that are multiplying each other and giving you a huge increase in fires,” he said. Using a model akin to the ones that forecast movements in the stock market, the scientists concluded that humans were the principal drivers of these fires, both through direct ignition and by the elimination of herbivores (elimination of herbivores allowed flammable underbrush to spread uncontained). Shifts in the climate aggravated this further, setting the stage for the extinction of species.