Size and Weight:
About the Giant Short-Faced Bear (Arctodus Simus):
Although it's often described as the largest bear that ever lived, the Giant Short-Faced Bear (Arctodus simus) didn't quite measure up to the modern Polar Bear--but it's hard to imagine the average megafauna mammal (or early human) worrying whether it was about to be eaten by an 1,800- or 2,000-pound beast. Simply put, the Giant Short-Faced Bear was one of the scariest predators of the Pleistocene epoch, full-grown adults rearing up to heights of 11 to 13 feet and capable of running at top speeds of 30 to 40 miles per hour. The main thing that distinguished this bear from that other famous ursine of the Pleistocene, the Cave Bear, is that Arctodus simus was slightly bigger, and subsisted mostly on meat (the Cave Bear being a strict vegetarian).
Because the Giant Short-Faced Bear isn't represented by nearly as many fossil specimens as the Cave Bear, there's still a lot we don't understand about its everyday life. In particular, paleontologists aren't sure about this bear's hunting style or preferred prey: with its presumed speed, the Giant Short-Faced Bear may have been capable of running down the small prehistoric horses of North America, but it doesn't seem to have been robustly built enough to tackle larger prey. One theory is that Arctodus simus was essentially a loafer, popping up suddenly after another predator had already hunted and killed its prey, driving the smaller carnivore away, and digging in for a tasty (and unearned) meal.