Determining the largest bear ever requires examining both extinct giants and massive modern species. Size estimates rely on skeletal evidence for ancient animals and careful measurement of living populations, often presenting a range rather than a fixed number. This exploration into bear size covers the colossal predators shaped by prehistoric ecosystems and extreme environments.
The Giant Short-Faced Bear
The title for the largest bear that ever lived most likely belongs to the extinct Giant Short-Faced Bear, Arctodus simus, which dominated Pleistocene North America. This colossal animal stood approximately five feet tall at the shoulder when walking on all fours, making it significantly taller than any modern bear species. When rising onto its hind legs, the largest males are estimated to have reached a towering height of up to 12 feet.
Weight estimates for Arctodus simus vary, but adult males were consistently immense, often cited between 1,600 and over 2,200 pounds. This weight far exceeded that of contemporary bears. Its skeletal structure featured long, slender limbs, suggesting it was built for speed and endurance, capable of running up to 40 miles per hour.
The bear’s name derives from its relatively short muzzle and broad snout, which housed powerful jaw muscles. Paleobiologists initially classified it as a hypercarnivore, meaning its diet consisted almost entirely of meat, a conclusion supported by bone sample analysis. While some studies suggest a more omnivorous or scavenging role, its physical adaptations point toward a life centered on hunting or dominating kills.
This giant roamed from Alaska and the Yukon down to the open country west of the Mississippi River, preying on or scavenging large Ice Age herbivores. Since size determinations are based on fossil reconstruction, the exact maximum weight remains a subject of scientific debate. Regardless, the enormous size of Arctodus simus makes it the most substantial bear known from the fossil record.
The Largest Bears Alive Today
Among bears alive today, the competition for the largest species is primarily between the Polar Bear (Ursus maritimus) and the Kodiak Bear (Ursus arctos middendorffi). The Polar Bear is generally considered the largest species on average, with adult males typically weighing between 775 and 1,300 pounds. The largest recorded Polar Bear specimen weighed over 2,200 pounds and stood nearly 12 feet tall on its hind legs.
Kodiak bears, a unique subspecies of brown bear found exclusively on the islands of the Kodiak Archipelago in Alaska, are close contenders. Wild adult male Kodiaks often reach up to 1,500 pounds and can stand about 10 feet tall when upright. While the average Polar Bear is often heavier, large Kodiak individuals can rival or even exceed the weight of many Polar Bears, making the comparison very close at the upper limits of their size range.
Polar Bears tend to be longer and more streamlined, an adaptation for their aquatic life hunting seals on sea ice. In contrast, Kodiak bears typically possess a more stocky and broader build, reflecting their terrestrial and coastal habitat. Both species display significant sexual dimorphism, with males often weighing twice as much as females.
Factors Driving Extreme Bear Size
The development of enormous body sizes in both extinct and living bears is closely tied to environmental and evolutionary pressures. A primary driver is Bergmann’s Rule, which states that populations living in colder climates tend to be larger than those in warmer regions. This size difference is an adaptation rooted in thermodynamics.
A large body mass has a smaller surface area-to-volume ratio compared to a smaller body. This allows larger animals, such as the Polar Bear or Arctodus simus, to radiate less body heat per unit of mass, which is highly advantageous for conserving warmth in frigid environments. This thermal regulation mechanism helps explain why the largest bears are found in the planet’s northernmost reaches.
Beyond temperature, resource availability also permits the evolution of large size. A consistently high-calorie diet is required to sustain a massive physique. For the Polar Bear, this means a diet rich in high-fat marine mammals, particularly seals. Similarly, the Giant Short-Faced Bear thrived on abundant large Ice Age herbivores, providing the necessary energy to maintain its size.