Bears are diverse mammals, varying significantly in size from smaller forest dwellers to massive apex predators. Their evolution has led to colossal forms, prompting curiosity about the largest bear that ever roamed Earth.
The Largest Bear to Ever Live
The largest bear known to have lived in North America was the Giant Short-Faced Bear, Arctodus simus. This formidable creature inhabited the continent during the Pleistocene epoch, 2.6 million to 12,800 years ago. Its geographical range was extensive, stretching from Alaska and Yukon down to Mexico, with fossil evidence also found as far east as Virginia and Florida.
Arctodus simus was an imposing animal, standing about 1.5 to 1.8 meters (5 to 6 feet) tall at the shoulder when on all fours. When standing on its hind legs, it could reach heights of 3.3 to 3.7 meters (11 to 12 feet). Adult males of this species could weigh between 800 and 1,000 kilograms (1,800 to 2,204 pounds).
The exact diet and hunting strategies of Arctodus simus have been subjects of scientific debate. Early assumptions suggested it was a powerful predator, but recent research indicates it may have been largely a scavenger, using its immense size to intimidate other carnivores. High levels of nitrogen-15 isotopes in its bones point to a meat-rich diet. Evidence also suggests it could run over 60 kilometers per hour (40 miles per hour), aiding in locating carcasses or pursuing prey.
Other Notable Giant Prehistoric Bears
While Arctodus simus dominated North America, other massive bears existed globally. The Cave Bear, Ursus spelaeus, lived across Europe and Asia during the Pleistocene epoch. These bears were considerably larger than modern brown bears, with males weighing between 350 and 600 kilograms (770 to 1,320 pounds). Some specimens reached up to 1,000 kilograms (2,200 pounds) and stood 3 to 3.5 meters (10 to 11.5 feet) tall on their hind legs.
Despite their formidable size, Cave Bears were primarily herbivorous, feeding mostly on vegetation. Their name comes from the abundance of remains found in caves, which they used for shelter and hibernation. Another significant prehistoric bear, potentially even larger than Arctodus simus, was the South American Giant Short-Faced Bear, Arctotherium angustidens. Found in South America, this bear is estimated to have weighed up to 1,588 kilograms (3,500 pounds). Some humerus bones nearly match an Asian elephant’s.
Today’s Largest Bears
Among living bear species, the Polar Bear (Ursus maritimus) and the Kodiak Bear (Ursus arctos middendorffi) are the largest. The Polar Bear, inhabiting the Arctic Circle, is considered the largest by average weight. Male Polar Bears weigh between 300 and 800 kilograms (660 to 1,760 pounds) and can stand 1.8 to 2.4 meters (6 to 8 feet) tall. The largest recorded Polar Bear weighed over 1,002 kilograms (2,209 pounds).
The Kodiak Bear, a subspecies of brown bear found exclusively on the Kodiak Archipelago in Alaska, is also immense. Adult male Kodiak Bears average 475 to 533 kilograms (1,050 to 1,175 pounds) and can stand 2.4 to 3 meters (8 to 10 feet) tall on their hind legs. While the largest individual Polar Bears may outweigh the largest Kodiak Bears, the Kodiak Bear often presents a bulkier build.
Why Bears Grew So Large
The immense size observed in some prehistoric and modern bears can be attributed to several biological and environmental factors. One concept is Bergmann’s Rule, which suggests individuals in colder climates tend to have larger body sizes. A larger body has a smaller surface area-to-volume ratio, helping retain body heat more efficiently in frigid environments. The Pleistocene Ice Age, characterized by extended cold periods, favored the evolution of larger animals.
Abundant food resources also played a role in the growth of these bears. During the Pleistocene, vast populations of megafauna, such as mammoths and bison, provided plentiful prey or carrion. A larger body size gave bears an advantage in hunting these large animals or competing with other predators for carcasses. This competitive pressure, coupled with a lack of significant predation on adult bears, allowed them to reach considerable sizes.
The omnivorous diet of many bear species, combined with the need to store energy for hibernation, contributed to their large stature. Bears consume vast amounts of food in preparation for winter dormancy, and larger individuals can accumulate more fat reserves. This ability to store substantial energy for survival during lean periods further drove the evolution of their impressive body mass.