Giant sloths vanished 13,000 years ago — now tied to wildfires

A new study shows large-scale fires drove the enigmatic disappearance of megafauna during the end-Pleistocene extinction event.
Sade Agard
Stock photo of wildfire.
Stock photo of wildfire.


A new study has shed light on the enigmatic extinction of Pleistocene megafauna in Southern California, revealing that the disappearance of these ancient giants was intricately tied to large-scale fires and a changing climate.

The research published in Science on August 17 utilized a new radiocarbon chronology of fossils extracted from the La Brea tar pits.

The findings not only offer insights into the past but also carries crucial implications for understanding future ecological impacts from wildfires today.

Pleistocene wildfires

“The conditions that led to the end-Pleistocene state shift in Southern California are recurring today across the western United States and in numerous other ecosystems worldwide,” wrote the authors in a press release.

"Understanding the interplay of climatic and anthropogenic changes in driving this past extinction event may be helpful in mitigating future biodiversity loss in the face of similar pressures.”

The Pleistocene epoch — about 2.6 million years ago to around 11,700 years ago— marked a dramatic period of Earth's history, characterized by giant creatures roaming the landscape. 

However, towards the end of this era, a substantial portion of these megafaunal species, such as mammoths, mastodons, ground sloths, and giant beavers, met their demise.

The magnitude of this extinction event, encompassing roughly two-thirds of large mammals globally, has long-puzzled scientists.

A recent study led by Frank O'Keefe from Marshall University, U.S., and his team, delved into the factors underpinning the extinction of megafauna in Southern California. 

The La Brea tar pits, renowned for preserving an extensive record of Pleistocene megafaunal occupation spanning over 55,000 years, provided the ideal repository for this investigation.

Giant sloths vanished 13,000 years ago — now tied to wildfires
La Brea Tar Pits fauna showing giant sloth trapped in a lake, as depicted by Charles R. Knight

Utilizing advanced radiocarbon dating techniques, the researchers meticulously analyzed fossils of megafaunal individuals, creating a high-resolution chronology that covered a pivotal period from 15.6 to 10 thousand years ago. 

Their meticulous work uncovered a striking pattern: seven of the most common mammal species had vanished from the region by 12.9 thousand years ago.

This disappearing act of megafauna at La Brea occurred notably earlier than the North American megafaunal extinction. Additionally, it coincided with changes in vegetation and increased aridity during the Bølling-Allerød warming event. 

Notably, this phase of pronounced climatic change also witnessed a surge in large-scale fire activity across the region.

The increase in fire activity, exacerbated by a warming and drying climate, created an environment ripe for the decline of these massive creatures. 

Human hunting practices and fire manipulation likely compounded these challenges, leading to a precarious ecosystem increasingly susceptible to catastrophic blazes.

The past is key to the future

Beyond unraveling the past, this study holds a mirror to the present and future. 

The researchers emphasize that the challenges faced by megafauna in the Pleistocene era eerily resonate with the contemporary shifts occurring across ecosystems worldwide. 

The impact of climate change, combined with human activities, forms a potent cocktail that threatens the delicate balance of many ecosystems today.

The complete study was published in Science on August 17 and can be found here

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