Arctodus

I thought that there was zero believability in the tagline saying the grizzly was 18 feet tall! This is an impossibility, isn't it? There isn't a bear on record anywhere this size.
But I just read a wiki article suggesting that this is supposed to be Arctodus, also called the short-faced bear, a prehistoric flesh-eating bear of the Plesticene, averaging 15 feet in height--what it actually was supposed to be in the film. Even Arctodus wasn't quite that size, but it was huge. It was also NOT a grizzly, or even the ancestor of one. They were different animals. The Arctodus evolved in North America, and the much smaller grizzly is a subspecies of brown bear that migrated from Asia during the ice-age. The bear in the movie though, is obviously just a grizzly. And even if it's supposed to be short-face, where did it come from?