Human-Caused Wildfires Spell Doom for Giant Sloths in California

Human-Caused Wildfires Spell Doom for Giant Sloths in California

In a recently published investigation called “Pre–Younger Dryas megafaunal extirpation at Rancho La Brea linked to fire-driven state shift,” Frank O’Keefe from Marshall University and his research team unfold the factors behind the disappearance of enormous prehistoric creatures in Southern California.


La Brea Tar Pits fauna showing giant sloth trapped in a lake, as depicted by Charles R. Knight


The famed La Brea tar pits, known for their extraordinary preservation of the Pleistocene megafauna’s history spanning an astonishing 55,000 years, became the perfect setting for this insightful inquiry.

The outcome of their study pointed to an astonishing revelation: during an epoch of warm and arid climate conditions, the presence of humans and their mastery over an uncontrollable tool – fire – led to the sudden disappearance of the remarkable Ice Age mammals.


Exploring the Study


Employing cutting-edge radiocarbon dating methods, the researchers examined fossils of megafaunal species. This meticulous work constructed a detailed timeline for the eight most prevalent mammal species at La Brea: sabertoothed cat (Smilodon fatalis), dire wolf (Aenocyon dirus), coyote (Canis latrans), American lion (Panthera atrox), ancient bison (Bison antiquus), western horse (Equus occidentalis), yesterday’s camel (Camelops hesternus), and Harlan’s ground sloth (Paramylodon harlani). This timeline covered a pivotal period from 15.6 to 10 thousand years ago.


Model of Harlan ground sloth (Paramylodon harlani)
Model of Harlan ground sloth (Paramylodon harlani). Check the 3D model animation here. 


Their precise analysis unveiled a remarkable pattern: seven of these common mammal species had vanished from the region by 12.9 thousand years ago. This disappearance of megafauna at La Brea occurred considerably earlier than the extinction of North American megafauna.


Climate Change and Wildfires

Between 14,000 and 13,000 years ago, a period of unusually warm and dry climate unfolded worldwide. Unlike today’s human-driven global warming, this prolonged warming phase was a natural event, a part of several climate fluctuations during the late ice age.

During this era of significant climatic transformation, the region experienced an upsurge in extensive fire activity.



The surge in wildfires, magnified by the warming and drying climate, created an environment ripe for the decline of these majestic creatures.“Human beings were accountable for these fires, and astonishingly, the fires coincided exactly with the complete disappearance of megafauna from the surroundings,” remarked Emily Lindsey, a curator at the La Brea Tar Pits and one of the study’s senior authors.

Another Human-Caused Extinction Event

Remarkably, the fossil records depict that this devastation occurred in a mere span of 200 years. “This stands as the most momentous extinction event since a meteor crashed into Earth, wiping out the large dinosaurs. It could very well be the initial pulse of the ongoing extinction crisis,” emphasized Lindsey.


humans hunting giant sloth
A recreation of humans hunting giant sloths / Illustration: Alex Macclelland, Bournemouth University


The notion of human hunters driving the megafauna extinction isn’t novel. Argentine researchers have put forth a study illustrating a sharp decline in megafauna populations coinciding with the emergence of fishtail-tipped spearheads. This suggests that as humans acquired this novel technology, they hunted these mammals, eventually contributing to their decline in South America.


Lessons from the Past

The most striking divergence between then and now is that all the elements that paved the way for the Ice Age mammals’ extinction are now more extensive, rapid, or potent.

As we alter landscapes, modify habitats, pollute air and water, and drive global warming, countless species are facing unprecedented challenges and are disappearing at an alarming rate. Tragically, this human-induced transformation of the environment has led to an unprecedented crisis – the sixth mass extinction event.


Wildfires across the globe have become a recurring phenomenon that continues to intensify.


This study serves as an extraordinary testament to our ability to glean insights from history and apply them to anticipate the future. As we mark this epoch by our presence, we must acknowledge the profound impact we wield and take urgent steps to address the mounting challenges that threaten countless species and the delicate balance of life on Earth.


‘Those who do not learn history are doomed to repeat it’

– George Santayana, Spanish philosopher


-Cecilia Pamich

Communications and Outreach

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