Bear teeth from Teeth.
This image proved invaluable when slogging my through the works of an extravagant taxonomist for The Patriarchal Bear. Long story short, he was probably full of crap.
The taxonomy of this image is a bit eccentric itself; ‘Thalarctos' is the polar bear (normally Ursus maritimus) and ‘Selenarctos' is the Asian Black Bear (normally Ursus thibetanus). Apparently ‘Ursus' encompasses both American Black and Brown Bears. The latter two bears belong to a separate branch known as tremarctines; Tremarctos is still extant (and known as Spectacled Bears) and Arctodus are the extinct deep-faced bears from North America.