Asian black bear
Biologically and morphologically, Asiatic black bears represent the beginning of the arboreal specializations attained by sloth bears and sun bears. Asiatic black bears have karyotypes nearly identical to those of the five other ursine bears, and, as is typical in the genus, they have 74 chromosomes. From an evolutionary perspective, Asiatic black bears are the least changed of Old World bears, with certain scientists arguing that it is likely that all other lineages of ursine bear stem from this species. Scientists have proposed that Asiatic black bears are either a surviving, albeit modified, form of "Ursus etruscus", specifically the early, small variety of the Middle Villafranchian (Upper Pliocene to Lower Pleistocene) or a larger form of "Ursus minimus", an extinct species that arose 4,000,000 years ago. With the exception of the age of the bones, it is often difficult to distinguish the remains of "Ursus minimus" with those of modern Asiatic black bears.
Short-faced bear
"Arctodus" moved in a pacing motion like a camel, horse, and modern bears, making it built more for endurance than for great speed. "A. simus", according to these arguments, was ill-equipped to be an active predator, leading some to conclude that it was a kleptoparasite, using its enormous size to intimidate smaller predators, such as dire wolves, saber-tooth cats, and American lions, or chase them from their kills and steal their food. This idea was challenged in a 2013 study of the micro-wear of the teeth of various extant and extinct bears. The researchers concluded that the short-faced bear was not a pure scavenger and in fact was even less of a scavenger than the modern polar bear. A 2010 study concluded that the species was neither a super-predator nor pure scavenger but an opportunistic omnivore like modern brown bears.