The question of the largest bear depends on whether one is referring to a species alive today or one that walked the earth long ago, and whether the measure of “biggest” is height, length, or total body mass. Understanding the true titans requires looking across both the fossil record and the most extreme environments on the planet.
The Largest Bear Ever Recorded
The title of the largest bear species to ever exist belongs to the South American Short-faced Bear, Arctotherium angustidens, a carnivore that lived during the Early Pleistocene epoch. Fossil evidence, particularly a huge humerus bone discovered in Buenos Aires, Argentina, points to an animal that dwarfs even the largest of today’s bears. Using proportional scaling techniques, scientists estimate the largest individuals of this species could have reached a body mass between 1,588 and 1,749 kilograms (3,501 to 3,856 pounds). This measurement is more than double the weight of the biggest modern bears.
Standing upright on its hind legs, this predator is estimated to have achieved a height between 3.4 and 4.3 meters (11.2 to 14.1 feet). Arctotherium angustidens was one of the largest terrestrial carnivorous mammals. While its North American cousin, the Giant Short-faced Bear (Arctodus simus), is often cited as the largest bear, the South American species holds the record for the highest estimated maximum weight. Arctodus simus stood about 1.5 meters (5 feet) at the shoulder and reached weights up to about 950 kilograms (2,100 pounds).
Both of these extinct giants were members of the Tremarctinae subfamily, which today is represented only by the much smaller Spectacled Bear. Arctotherium angustidens thrived after migrating to South America during the Great American Interchange, where it faced little competition from other large predators. Its immense size suggests an opportunistic ecology, likely involving taking down large prey or dominating scavenging opportunities. The species eventually died out around 800,000 years ago.
The Modern Giants: Polar Bear vs. Kodiak Bear
Among the species living today, the two contenders for the largest bear are the Polar Bear (Ursus maritimus) and the Kodiak Bear (Ursus arctos middendorffi), a subspecies of brown bear. The Polar Bear is generally recognized as the largest species, capable of reaching the highest absolute weights.
Adult male polar bears typically weigh between 450 to 544 kilograms (990 to 1,200 pounds), though large individuals have been documented exceeding 800 kilograms. The largest recorded male polar bear reached 1,002 kilograms (2,209 pounds), securing its status as the world’s heaviest living bear. These Arctic predators tend to be longer and more streamlined than brown bears, measuring up to 3 meters (10 feet) in body length. Their size is an adaptation to their cold habitat, helping them conserve heat while hunting seals on the sea ice.
The Kodiak Bear, restricted to the Kodiak Archipelago in Alaska, represents the largest subspecies of brown bear. Mature Kodiak males often weigh between 475 and 533 kilograms (1,050 to 1,175 pounds), making their average weight comparable to the average polar bear. While the maximum recorded weight for a wild Kodiak bear is slightly less than the polar bear’s record, they possess a stockier, broader build.
Kodiak bears are notably bulky, with some individuals standing over 3 meters (10 feet) tall when fully upright. Their size is fueled by the abundant food resources of their island habitat, particularly the nutrient-rich annual salmon runs. The debate over which modern bear is largest often concludes that the Polar Bear has the greater maximum weight and length, while the Kodiak Bear is the most robust in overall build.
Determining Size: Paleontology and Evolutionary Scale
Establishing the size of an extinct species relies on scientific techniques, as paleontologists cannot place a fossilized animal on a scale. The most reliable method uses mathematical scaling relationships derived from the bones of living animals with known masses. Dimensions of load-bearing bones, such as the circumference of the femur or humerus, are tightly correlated with body mass in all terrestrial vertebrates.
By measuring the circumference of these fossilized limb bones, researchers apply established equations to estimate the total body mass of the extinct bear. This technique is necessary because an animal’s total weight relates to the stress its skeleton must bear, requiring proportionally thicker bones for heavier animals. The larger the bone circumference, the greater the predicted body weight. However, the choice of reference species for the scaling can influence the final result.
The evolution of massive size in both extinct and modern bears aligns with Bergmann’s Rule. This principle suggests that individuals in colder climates tend to be larger than those in warmer regions within a related group. This is based on the surface area-to-volume ratio, where a larger body mass has proportionally less surface area through which to lose heat. This adaptation explains why the Polar Bear is the largest living species in the Arctic and why many large prehistoric bears thrived in the Ice Age.