Discover the 4,000 lb. Bear That Was the Largest Ever

Today’s bears are some of the largest land carnivores in the world. With reputations as fiercely protective mothers, even modern bears are no match for the 4,000-pound bears that lived in prehistoric times. The Arctotherium angustidens could weigh up to 4,000 pounds and towered over many other animals that lived at the time. Now extinct, the Arctotherium angustidens is distantly related to the modern Spectacled bear.

What were these enormous bears like and how did they fit into the prehistoric animal kingdom? Learn more about where and how they lived, as well as what it took to reach their remarkable size.

Description & Size

These bears were often between 2,000 and 4,000 pounds, making them the largest bears ever discovered. Males were typically larger than females. They stood around 11 and 14 feet tall. Their immense size was more noticeable in their bulk than in their height. They carried the extra weight mostly in their muscular bodies and legs.

Arctotherium angustidens are sometimes referred to as short-faced bears due to their shorter snouts. With their immense bodies, their shorter faces were even more pronounced and noticeable compared to modern bears. Other short-faced bears include members of the Tremarctinae sub-family. Most are now extinct, but the Spectacled bear remains. It is also native to South America.

The largest modern bears are the Kodiak Brown Bears who live in the Kodiak region of Alaska. But even these bears are a fraction of the overall size of the Arctotherium angustidens. The giant bears were as much as two times the weight of modern Kodiaks.

Arctotherium angustidens Scientific Classification

What Did Arctotherium angustidens Eat?

To maintain their large size, Arctotherium angustidens had to eat a lot. Like many other bears, they were omnivores and opportunistic feeders. They ate berries, leaves, carrion, and other animals. They liked fish and would often eat plenty of fish and berries in preparation for a long winter hibernation period. These bears probably ate more meat than other bears before or since.

Most researchers believe that Arctotherium angustidens was more of a carnivore than other bears that evolved later. As bears of the period evolved alongside and after the Arctotherium angustidens were considerably smaller. Scientists believe that this occurred due to increasing competition for meat and protein. When Arctotherium angustidens first evolved, there were few other predators that could hold their own against one of these giant bears. Because of this, the Arctotherium angustidens had greater access to food and resources.

Analysis of fossilized teeth shows that their jaws were powerful enough to crush bone. This helped them eat meat to maintain their large size. While they likely hunted to eat, Arctotherium angustidens probably chased off other carnivores to steal meals that were already killed as well. They were not too picky to enjoy carrion.

Arctotherium angustidens often used their immense size to overpower potential prey. When other animals wandered into their den, these bears were more likely to chase them away rather than continue the hunt. That didn’t stop them from enjoying a delicious morsel, however, when it did come to mealtime. If these animals were unlucky enough to find a hungry Arctotherium angustidens, they were more likely to become the next meal.

Habitat – When and Where It Lived

These bears lived primarily in South America during the Pleistocene epoch, between 2.6 million and 11,700 years ago. They eventually made their way to Central America and eventually North America at the end of this period. During this time, about 700,000 years ago, the gigantic Arctotherium angustidens died out as a species, but its descendents evolved into other species of smaller bears.

Scientists have found evidence of these large bears in South America, near Bueno Aires. Scientists used genetic analysis to learn more about how these fossilized bears fit into the evolution of their scientific family, Ursidae. Modern bears are also part of the Ursidae family.

Arctotherium angustidens lived in caves during winter hibernation and even favored their dens at other points as well. Mother bears protected their more vulnerable cubs in these dens, similar to modern bears. They could be highly protective mothers and would attack any potential predators who came too close.

Threats and Predators

As one of the largest land mammals of its time (or any time), Arctotherium angustidens didn’t face a threat from many predators. The animals that did go after these bears often targeted young cubs or older, weak bears. Mother bears were fiercely protective and could keep their cubs safe from most potential predators. Saber-tooth tigers were the largest meat-eaters of the time that lived in the same places. They were likely no match for an adult Arctotherium angustidens, however.

Their underbellies were their most vulnerable point. Because of this, most Arctotherium angustidens bears avoided rising on their hindlegs, especially during a fight. Adult Arctotherium angustidens likely fought other bears of the species over territory and resources.

Scientists believe that the Arctotherium angustidens was able to attain such a large size because it did not have a lot of competition for animal protein to eat. It lived in a relatively small area. As the species expanded into Central and North America, smaller bears that could sustain themselves on a wider variety of foods had an advantage over the Arctotherium angustidens when it came to survival.

All bears face the threat of illness, starvation, and exposure to the elements during hibernation. Competition over resources and shelter between bears was one of the most formidable threats that these giant animals faced. Without enough food, adult Arctotherium angustidens succumbed to the elements or illness during these long hibernation periods.

Discoveries and Fossils – Where It Was Found

Researchers found a gigantic fossilized Arctotherium angustidens near Buenos Aires, Argentina in 2011. The femur bones helped scientists determine how large the bear was overall. They estimated that it stood more than 11 feet tall and weighed around 4,000 pounds.

This made the Arctotherium angustidens much larger than any other bear at the time. It is the largest specimen of the largest bear species known to ever exist. Their diet that was rich in protein helped them attain this large size. Fossils of other bears that evolved in parallel with the Arctotherium angustidens and after showed smaller sizes. These bears relied more on vegetation, which contributed to their smaller size as well as their survival.

This specimen was a male. Female Arctotherium angustidens were much smaller, similar to other bear species at the time and since. Other discoveries include fossils such as bones, teeth, and skulls that help researchers understand both size and genetic development. They also use these specimens to learn more about what these bears ate.

Fossils of other species of the genus have been found in Bolivia, El Salvador, Argentina, Brazil, Chile, and Central America. All of these species have since become extinct. The Arctotherium angustidens is the largest known example and weighed as much as 2,000 pounds more than other large bears of the period.

Extinction – Why Did It Die Out?

When Arctotherium angustidens first evolved in South America, there were few other predators that could compete with them for food and resources. But because they favored animal protein and needed so much to maintain their large size, these bears had to eat a lot to survive.

Over time, smaller bears that were able to survive on more plentiful food options, including berries, vegetation, and fish, survived at a higher rate. The Arctotherium genus included other species of smaller bears, such as the A. bonariense, A. tarijense, A. vetustum, and A. wingei. While now extinct, scientists believe that these species survived past the Arctotherium angustidens.

The modern Spectacled bear is the only remaining short-faced bear in existence and the last surviving member of the Tremarctinae sub-family of bears. Scientists believe that these bears evolved from other species of prehistoric bears.

Similar Animals to the Arctotherium angustidens

Other bears at the time and since were large but none compare to the Arctotherium angustidens in size.

• Kodiak bear: The largest modern bear, Kodiak bears top off around 2,000 pounds. These bears eat both plants and animals. They also hibernate, just like the Arctotherium angustidens. Kodiak bears are a species of Brown Bear, sometimes known as the Alaskan Brown Bear.
• Spectacled bear: These bears, native to South America, are the closest living relative to Arctotherium angustidens. They are the only remaining species in the sub-family Tremarctinae. These South American bears are also omnivores, although they eat more berries and vegetation than their ancient relatives. They are quite a bit smaller, getting up to 440 pounds.
• Cave bear: Another extinct bear, the Ursus spelaeus could get up to 2,200 pounds. They were also large predators of the time. Their territory was considerably larger and evidence of cave bears exists on every continent other than Antarctica and Australia.

How Is Arctotherium Different from Arctodus?

Arctotherium is a genus in the subfamily Tremarctinae, and so is Arctodus. Both genera are extinct, but there is one living member of the Tremarctinae subfamily, and that is the spectacled bear (mentioned above) of South America.

The Arctodus genus had two species: pristinus and simus. Both went extinct in the Pleistocene: pristinus about 300,000 years ago (400,000 years after A. angustidens) and simus about 12,000 years ago. Arctodus was one of the more widespread in North America and was one of the last megafauna to go extinct.

Both Arctotherium and Arctodus were giant short-faced bears and are considered an example of convergent evolution (the independent evolution of similar features in species of different periods). However, Arctotherium angustidens was a heavier, more robust bear; it could reach up to 2,600 pounds while the Arctodus simus maxed out at about 2110 pounds.

The photo featured at the top of this post is © Daniel Eskridge/Shutterstock.com