An Ultimate Guide to Arctotherium: The Bear Beast

Leave a comment / / Updated on: 25th September 2023

Name MeaningBear beastHeight3.4–4.3 meters (11–14 feet)
Pronunciationark-toe-THERE-ee-umLength3 meters (9.8 feet) 
EraCenozoic – Quaternary PeriodWeight1,200 kilograms (2,646 pounds)
ClassificationMammalia, Carnivora, & UrsidaeLocationArgentina (South America)

Arctotherium Pictures

Life restoration of Arctotherium bonariense
Life restoration of Arctotherium bonariense | Robert Bruce Horsfall via Wikipedia Public Domain

The Arctotherium

Gage Beasley Prehistoric's Arctotherium Concept
Gage Beasley Prehistoric’s Arctotherium Concept

Bears are among the most beastly animals today. 

Even though they’re mostly herbivores or omnivores, bears are just as aggressive and dangerous as some of the biggest carnivores around. 

The biggest of them can stand up to a height of about 1.5 meters (4.9 feet) and weigh about 751 kilograms (1,656 pounds). 

Now imagine just how big a bear has to be for it to be named “the bear beast.” 

Arctotherium was the biggest bear that has ever lived. 

This genus of short-faced bears lived in South America from the Late Pliocene till the end of the Pleistocene Epoch.

An Arctotherium during the quaternary period
An Arctotherium during the quaternary period | Gojira2018 via Prehistoric Earth: A Natural History Wiki

Arctotherium descended from North American bear species that migrated to South America during the Great American Exchange during the Late Pliocene Epoch roughly three million years ago.  

They’re most closely related to the living spectacled bear, which is nowhere near the impressive size of their extinct relative. 

There are five different species in the genus, characterized by differences in their overall size and other distinctions in their appearance. 

This article provides a general overview of this massive bear, including what it looked like and how it lived. 

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Physical Characteristics

A Kodiak bear for reference
A Kodiak bear for reference | Yathin S Krishnappa via Wikipedia CC BY-SA 3.0

Arctotherium is commonly referred to as the South American short-faced bear. 

This bear’s common name helps distinguish it from the North American short-faced bear and also references its relatively short and broad face. 

In terms of its size, this bear is on par with some of the largest bear species today, like the Kodiak bear and the polar bear. 

However, it had a more robust build compared to these bear species, which is why it is often described as the largest bear that has ever lived. 

Arctotherium bears demonstrated notable differences in size across the different species. 

Their weight ranged from 51 to 150 kilograms (112–331 pounds) for the smallest species in the genus (Arctotherium wingei) to as much as 1,200 kilograms (2,646 pounds) for the largest species (Arctotherium angustidens).

Gage Beasley Prehistoric's Arctotherium Size Comparison Chart
Gage Beasley Prehistoric’s Arctotherium Size Comparison Chart

This species also had a standing weight that ranged between 3.4 and 4.3 m (11–14 feet). 

Based on this size estimate, Arctotherium angustidens is considered the largest bear species that has ever lived. 

This also makes it the largest carnivorous land mammal discovered so far. 

Remarkably, the largest species is the oldest in the genus. 

This was replaced by medium-sized species after it went extinct about 0.7 million years ago. 

The decrease in size observed for this genus was probably a response to heightened competition in their habitat, causing the bear’s diet to shift from primarily carnivorous to omnivorous or herbivorous. 

Habitat and Distribution

Arctotherium lived in South America during the Pleistocene Epoch. 

The genus had a wide geographic range, with its fossils found in various parts of the continent, including Argentina, Brazil, Chile, and Uruguay. 

The ecosystem in South America during the Pleistocene was a mix of grasslands, savannas, woodlands, and scrublands. 

This provided a diverse array of habitats for various animal species, including the Arctotherium

Some scientists think the difference in size for the different species within the group was probably an adaptation to the diverse range of habitats that the different species lived within South America.

But Arctotherium bears weren’t always so widespread. 

At some point, almost all the species in the genus lived exclusively in the Southern Cone of South America, particularly present-day Argentina. 

They were most abundant in the Buenos Aires Province.

At some point, only two species lived outside Argentina. 

 A. vetustum lived in Brazil, and A. wingei lived on the northern edge of the continent. 

Arctotherium wingei was an extinct tremarctine bear from South America
Arctotherium wingei was an extinct tremarctine bear from South America | Image via Reddit

This changed during the Late Pleistocene as some previously endemic species spread to other parts of the continent. 

A. tarijense lived in the open plains and arid grasslands of present-day Argentina, Chile, Southern Bolivia, and Uruguay during the Late Pleistocene. 

Arctotherium tarijense surveying the surrounding landscape
Arctotherium tarijense surveying the surrounding landscape | Image via Reddit

Another species (A. bonariense) lived alongside A. tarijense in Uruguay. 

The climate in Pleistocene South America was generally cooler than present-day conditions. 

It was characterized by the presence of glaciers and ice sheets in various parts of the world, including some parts of South America. 

The planet experienced several ice ages with colder temperatures, followed by warmer interglacial periods. 

These climatic variations influenced the distribution of habitats and the species that could thrive in different regions.

The species that lived in the Northernmost region of South America (A. wingei) crossed over to Central America, going as far north as Yucatán in Mexico. 

Behavior and Diet

Given its massive size, Arctotherium’s movement might have been relatively slow and deliberate.

Yet, like modern bears, it would have been capable of quick bursts of speed, especially when hunting or defending its territory.

Arctotherium from the perspective of its prey
Arctotherium from the perspective of its prey | Gojira2018 via BloodRayne & Mia, the Vampire Slayer Wiki

This bear’s feet look like they were well-adapted for powerful digging and swiping motions. 

This would have been useful for hunting and scavenging. 

Some Arctotherium species, such as A. wingei, showed some semi-arboreal adaptations based on the shape of their elbow joint. 

But the size of this joint and the general size of the bear suggests that they were incapable of climbing trees. 

But the Arctotherium still retained some level of dexterity, especially in their forelimbs, similar to that of modern-day pandas. 

Arctotherium is generally considered to have been a solitary animal. 

Females probably lived with the juveniles as they developed, but males were most likely solitary and territorial. 

The small family groups made of a female and her cubs likely lived in dens during harsh climatic conditions, a sort of quasi-hibernation necessary for their survival. 

Black Bear mother and cubs in den hibernating
Black Bear mother and cubs in den hibernating | National Park Service via Wikipedia Public Domain

The size of this bear and the limited resources in its environment supports the idea that the males lived alone and probably defended their territory widely. 

Their population was quite low, reducing the likelihood of frequent encounters between individuals. 

However, interactions could have occurred during mating seasons or when competing for food resources.

The different species within the Arctotherium genus exhibited varying dietary preferences. 

Their diet changed from mainly carnivorous, omnivorous, and even herbivorous as the Pleistocene Epoch progressed. 

A. angustidens was largely carnivorous or omnivorous. 

It preyed actively on large vertebrates within its ecosystem, including horses, camelids, tapirs, and ground sloths but was a scavenger as well. 

On the other hand, A. bonariense & A. tarijense were cosmopolitan omnivores, while A. wingei as an herbivore. 

Arctotherium climbs a tree to keep its kill away from a predator
Arctotherium climbs a tree to keep its kill away from a predator | Image via Reddit

It is worth noting that this short-faced bear was highly adaptable, and the herbivorous species likely reverted to a carnivorous diet during periods of drought. 

The hunting behavior of the predatory Arctotherium is often compared to that of the spectacled bear. 

It probably involved ambushing prey and delivering surprise attacks to immobilize prey, after which the animal would be consumed alive. 

The large size of this bear meant it could easily pin down large prey with its large paws using its weight and long claws. 

Arctotherium was probably capable of pursuing prey actively as well. 

This bear was also large enough to intimidate other predators in its ecosystem, stealing prey from them. 

Arctotherium seizes the opportunity to steal food from two other predators
Arctotherium seizes the opportunity to steal food from two other predators | Image via Reddit

Life Cycle

The reproductive behavior and life cycle of the Arctotherium was probably similar to that of modern bears. 

They reproduced sexually, with the males and females coming together during mating season. 

It isn’t clear if they exhibited any sort of sexual behavior or if this behavior varied for the different species in the genus. 

After mating, female Arctotherium would have given birth to live young after a long gestation period. 

Arctotherium individuals likely gave birth to relatively small litters of cubs, with a maximum of two at a time. 

The cubs would have been born relatively undeveloped and would have required care and protection from their mother.

Like modern bears, the cubs would have grown rapidly during their early years.

A pair of Grizzly bear (Ursus arctos horribilis) cubs for comparison
A pair of Grizzly bear (Ursus arctos horribilis) cubs for comparison | Image via Wikimedia Public Domain

They consumed milk from their mothers but gradually adapted to feeding on solid food. 

The large size of this bear at maturity suggests that their developing years as juveniles were characterized by significant growth, which may have slowed down slightly after attaining maturity. 

Evolution and History

Arctotherium is part of the larger family of bears known as the Ursidae. 

The earliest ursids, such as the Allocyon, evolved in the Early Oligocene, about 34 to 30 million years ago. 

These primitive bears, including the direct ancestors of Arctotherium, evolved in North America. 

Plionarctos, a North American short-faced bear, is considered the direct ancestor of the Arctotherium.

Life restoration Plionarctos
Life restoration Plionarctos | Indominius Rex via Prehistoria Fandom

It evolved in North America about 13 million years ago and migrated to South America during the Great American Interchange about two million years ago. 

The first Arctotherium species that evolved following the dispersal of the genus to South America were A. vetustum and A. wingei

The largest species in the genus (A. angustidens) emerged during the Early Pleistocene and was alive till about 0.7 million years ago. 

A. bonariense and A. tarijense were the youngest species in the genus.

An Arctotherium bonariense with other contemporary mammals of its time
An Arctotherium bonariense with other contemporary mammals of its time | Image via Reddit

Over its evolutionary history, Arctotherium underwent significant changes in size. 

Their dentition also changed over time to match their diet 

These changes and the differences in their diet were responses to environmental pressures such as scarcity of resources and the presence of competitors in their ecosystem. 

Interactions With Other Species

Arctotherium was one of the most dominant animals in South America during the Pleistocene Epoch. 

As a predator, it would have had to compete with other large predators in its ecosystem, such as the saber-toothed cats like Smilodon, Theriodictis platensis, Protocyon scagliorum, prehistoric pumas, and jaguars in its habitats.

Arctotherium wingei confronting a Jaguar
Arctotherium wingei confronting a Jaguar | Image via Reddit

Their interactions with these predators would have included competition for prey and fight over kills and carcasses. 

Occasional clashes between Arctotherium and these other carnivores were likely common. 

Arctotherium’s prey would have included large herbivores that were part of the South American megafauna, including giant ground sloths, glyptodonts, horses, tapirs, and so on. 

An Arctotherium tarijense attacks a Sea Lion
An Arctotherium tarijense attacks a Sea Lion | Image via Reddit

The Arctotherium’s massive size would have given it an edge over some of the other predators in its ecosystem. 

But arguably, its biggest advantage over competitors was its ability to adapt its diet based on the available resources. 

This ensured the continued survival of this bear despite competition from invasive species coming into South America from North America throughout the Pleistocene. 

Cultural Significance

Arctotherium is known today as the biggest bear species to have ever lived. 

This is no easy feat because the Ursidae family has some very large members, including living and extinct species. 

Some of them, like the living Kodiak bear and polar bear, were roughly the same size as the Arctotherium but were less bulky. 

The size of this bear is the major reason why many people (both scientists and non-scientists find it fascinating).

Arctotherium angustidens was a giant bear from the Pleistocene of South America
Arctotherium angustidens was a giant bear from the Pleistocene of South America | Carl Buell via Reddit

Studying this bear has provided scientists with some valuable insights, especially about the evolution of these prehistoric mammals. 

As a large apex predator that doubled as a scavenger, Arctotherium has also helped scientists to better understand the dynamics of the ecosystem where they lived. 

Arctotherium was alive until as recently as 10,000 years ago. 

The relatively recent extinction of this bear makes it a valuable genus to unravel the factors contributing to the extinction of previously dominant prehistoric animals to preserve endangered species. 


Arctotherium was a genus of short-faced bears that lived in South America during the Pleistocene Epoch. 

The ancestors of this bear migrated to South America from North America about two million years ago, after which they evolved into various forms. 

One species in the genus evolved to become the largest bear to have ever lived and one of the largest terrestrial carnivores ever. 

But they weren’t all top predators. 

Some Arctotherium species were omnivores, while some were herbivores. 

Their ability to adjust and survive in different ecological niches allowed this bear genus to flourish for up to two million years before their eventual extinction a few thousand years ago. 


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