The short-faced bear also known as Arctodus is an extinct bear that inhabited North America during the Pleistocene epoch from about 1.8 million years ago until 11,000 years ago. It was the most common early North American bear and was most abundant in California. The short-faced bear was bigger than the grizzly bear and any predator of its time because walking on all 4 legs. A grizzly bear is about 1 m tall at the shoulder while the short-faced bear was 6 feet tall and while standing up, it stood 11 to 12 feet tall and weighed up to 2,500 pounds. Researchers disagree on the diet of Arctodus. Analysis of their bones showed high concentrations of nitrogen-15, a stable nitrogen isotope accumulated by meat-eaters, with no evidence of ingestion of vegetation. Based on this evidence, this bear was highly carnivorous and as an adult would have required 35.3 lb of flesh per day to survive. One proposal for its predatory habits envisages A. simus as a brutish predator that overwhelmed the large mammals of the Pleistocene with its great physical strength. However, despite being very large, its limbs were too gracile for such an attack strategy. Because its long legs enabled it to run at speeds of 30–40 mph, an alternative hypothesis is that it may have hunted by running down Pleistocene herbivores, such as wild horses and saiga antelopes, in a cheetah-like fashion, at one time earning it the name "running bear". However, during pursuit of speedy game animals, the bear's sheer physical mass would be a handicap. Arctodus skeletons do not articulate in a way that would have allowed for quick turns, an ability required of any predator that survives by killing agile prey.  It has been proposed that a large air burst or earth impact from one or more comets from outer space, impacting North America initiating the Younger Dryas which caused wildfires and environmental catastrophes led to the extinction of North American Pleistocene megafauna, including the short-faced bear together with the demise of the Clovis culture.