"North American giant short-faced bears have been ascribed at times to various taxa and have undergone several revisions: Arctotherium simum Cope, 1879 (genus from Bravard, 1857); Arctotherium yukonense Lambe, 1911; Arctotherium californicum Merriam, 1911; Dinarctotherium merriami Barbour, 1916; Tremarctotherium simum (Cope, 1879) (genus from Kra-glievich, 1926; used by Rinker, 1949); Arctodus nebrascensis (used by Berger, 1930; genus from Leidy, 1854); and Arctodus simus nebrascensis (used by Frick, 1930). These taxa are now considered to be junior synonyms of Arctodus simus (Cope, 1879), subfamily Tremarctinae, family Ursidae (Kurten, 1963). At one time, all North American Arctodus fossils were tentatively referred to a single species, Arctodus pristinus Leidy, 1854, and thought to be highly variable (Firby, 1968; Kurten, 1963). As more specimens became available, two species were recognized (Kurten, 1967). Arctodus pristinus Leidy, 1854 (junior synonym: Ursus haplodon Cope, 1896) was a relatively lightly built form with slender bones, relatively longer jaws, and smaller teeth than the larger A. simus. A. pristinus has been recognized with certainty only in eastern North America from middle Irvingtonian through Rancholabrean deposits (Kurten, 1967; Kurten and Anderson, 1980). A. simus is larger, has a more robust dentition and skeleton, a shorter face, and relatively longer limbs than A. pristinus. Remains of A. simus are found throughout North America (except in the southeast) and also date from middle Irvingtonian through Rancholabrean times (Kurten, 1967; Kurten and Anderson, 1980). Kurten (1967) recognized two subspecies of A. simus: the larger A. s. yukonensis from Yukon Territory, Alaska, and Nebraska and the smaller A. s. simus recovered throughout the rest of North America."
One thing to note, as I understand it, GSFB remains have now been found in the southeast USA. Also, A. pristinus is referred to as the lesser short-faced bear.
The Yukon skull (521 mm) is the largest one collected. We do not have skull or dental samples for the A. angustidens, or the other comparable size North American heavyweights from CA, UT, & NE. As I said before, a review of fossil dental records will also prove useful especially in relations to the large Yukon skull. I know there has been data covering this but I do not know that information off of the top of my head (I would need to look through my files for relating material) but at some point soon (I hope) I can make the inquiry.