Brown/Grizzly Bears
Eurasian Brown Bear
During the Mindel glaciation, cave bears in Europe marked the tip of one branch of Etruscan bear evolution. Simultaneously, at the other end of Eurasia, another branch budded U. arctos
(Fig. 2:10). The earliest remains of the brown bear have been found at the Peking Man site at Choukoutien, near Beijing, China. These bears were as large as European cave bears. (Kurte'n 1976). U. arctos is one of the most widely distributed wild mammals in the world (Nowak & Paradiso 1983), second only to the lion, as well as humans and domestic animals, mice and rats (Kurte'n 1976).
Historical distribution of U. arctos is comprehensively reviewed by Erdbrink (1953) and Kurte'n (1968, 1976) (Fig. 1:3). From China, brown bears spread north and east through Manchuria to the Pacific coast and throughout Siberia, as well as westward through the steppes and forests of northern Asia. I have found no record of brown bears inhabiting the arctic tundra of Asia comparable to "barren ground" grizzly bears in northern Alaska and Canada.
To the south, by contrast, spread of brown bear range was blocked by great arid zones 
(Fig. 2:11). Brown bears may have reached the Tian Shan mountains during a period when surrounding lands were more hospitable, then remained as a more-or-less isolated population as the surroundings became arid. Brown bears also spread westward through temperate parts of southern Asia: the Himalayas, Zargos Mountains, Caucasus, and Trancaucasus, and onto the Anatolia Peninsula. This included at least the northern mountain regions of Iran, Afghanistan, and Syria.
(Fig. 2:11). Brown bears may have reached the Tian Shan mountains during a period when surrounding lands were more hospitable, then remained as a more-or-less isolated population as the surroundings became arid. Brown bears also spread westward through temperate parts of southern Asia: the Himalayas, Zargos Mountains, Caucasus, and Trancaucasus, and onto the Anatolia Peninsula. This included at least the northern mountain regions of Iran, Afghanistan, and Syria. Browns bears reached Europe during the Eemian interglacial, ranging from northern Italy as high as Scandinavia, and eventually occupying the British Isles. During the Eemian and Weichselian, Britain was the European stronghold of the brown bear--habitat where the cave bear was rare. Brown bears survived in Ireland into the Holocene and were still seen in the mountains of Scotland in the 11th century. Some of these bears were much larger than extant specimens. Brown bears also crossed the Strait of Gibralter into the Atlas Mountains of Algeria and Morroco. (Kurte'n 1976). Brown bears (sometimes designated as U. crowtheri) survived in the Atlas Mountains until the early 1900's. (Couturier 1954:211).
Brown vs. Grizzly Bears: Taxonomy
In accordance with findings by Rausch (1963), Kurte'n & Anderson (1980) recognize 3 morphological groups of extant U. arctos in North America and Siberia: (1) The large bodied, broad-skulled brown bears of the Kamchatka Peninsula in Siberia and grizzly bears of Kodiak, Shuyak, and Afognak Islands in Alaska
(U. a. middendorfii), which may collectively be called "Kodiak" bears; (2) the large, narrow-skulled "brown/grizzly" bears (U. a. dalli) of the Alaska Peninsula and along the Pacific Coast down to British Columbia, perhaps including the now-extinct California race; (3) the smaller, narrow-skulled "grizzly" bears of inland North America (U. a. horribilis). There are additional subspecies in Asia, from the Pacific coast west to Europe (Novikov 1962). The particularly small brown bears of Europe (U. a. arctos) lie at the opposite end of the evolutionary and geographic gradient from grizzlies.
It is possible that each of the 3 morphological groups of U. arctos in North America--Kodiak bears, coastal grizzly/brown bears, and inland grizzlies--are descendants of separate waves of colonists from Asia onto this continent. Given that the earliest brown bears, found in China, were as large as modern Kodiaks (Kurte'n 1976) on Kamchatka and in Alaska, one might suppose that Kodiaks represent the earliest wave of colonists to North America. However, the only opportunity for such colonization was during glaciations, when Beringia was above sea level. The only known colonization occurred during the Wisconsinan glaciation.
The largest grizzly/brown bears occur in what seem to be the richest habitats (Stringham 1980, 1990a; Bunnell & Tait 1981). Greater abundance of food, producing larger bears with heavier jaw muscles, or differences in "chewiness" of food affecting jaw musculature, might have affected skull morphology genetically and/or epigentically (Section VI). So the 3 main groups of North American U. arctos identified by Rausch (1963) might be epigenetic ecotypes with little or no consistent genetic differences between groups. This is an hypothesis whose testing requires biochemical data.
Given these uncertainties about genetic relatedness of the different phenotypes, I will just group all U. arctos into 2 continental metapopulations, American grizzlies and Eurasian brown bears.
Grizzly Bear
Brown bear reached North America during the Wisconsinan glaciation, initially sharing the Alaska-Yukon refugium with the more predatory and larger giant short-faced bear, and remaining there after short-faced bears were extinct. It was not until retreat of the continental ice sheet during postglacial times that the brown/grizzly bear spread southward and eastward through rest of North America, where it was associated with A. simus at only 1 fossil site (Kurte'n 1968; Kurte'n & Anderson 1980; Martinka 1976:148).
Even within historical times, montane and plains grizzlies were distributed though much of western North America from Alaska south into northwestern Mexico where a few may still survive. (Fig. 1:3). South of Canada, grizzlies lived as far east as Hudson's Bay in Canada and the western boundary Minnesota (Rausch 1963; Herrero 1972, 1978; Banfield 1958, 1974; Hall 1981).
Barren ground grizzlies occur on the Arctic tundra from Alaska east to Hudson's Bay. Although never common on the Canadian barrens in historical times, their numbers seemed to be increasing as of the mid-1960's (Banfield 1958). There is controversy over how far eastward barren ground grizzlies once spread through Canada. Elton (1954) reviewed information from the Hudson's Bay Trading Co. and other sources on skins of what were apparently barren ground grizzly bears, supposedly killed on the Ungava Peninsula, just east of Hudson's Bay in northern Ontario during the 19th century.
Skeptics argue that these skins may be from light-colored black bears. While the light phase is now unusual in eastern North America, it might have been more prevalent before the advent of modern firearms--as has been documented in the southeastern United States (True 1882). Farther north, non-black individuals are rare in New York (Black 1958) and non-existent in Vermont (Willey, pers. comm.)--although hunters in central Vermont told me of killing reddish-brown bears as recently as the 1960's. Selective elimination of light-phase bears in the East may be due both to their initial rarity and perhaps greater conspicuousness in those habitats.
Various post-cranial fragments and 1 full skull thought to be from grizzlies have been found elsewhere in Ontario, The full skull, from Lake Simcoe, is for an immature bear (unfused basiooccipital-basisphenoid suture) with a condylobasal length of 322 mm and cheek tooth length of 75.8 mm; it was carbon dated as late Pleistocene (Peterson 1965). Spiess (1976) reports a single skull from an adult female grizzly found in an 18th century Eskimo midden in Labrador, with a condylobasal length of 265-270 mm and a P4-M2 length of 65 mm. If the Ontario and Labrador skins and skulls are from grizzlies, were they carried east of Hudson's Bay by humans? If the skulls are not really grizzly, could they be from some of the "giant" black bears that even now occur in the northeast (Ch. 7:I.C.). Peterson (1965) and Spiess (1976) did not give normal ranges for P4-M2 tooth lengths in grizzly vs. black bears. Nor did they give separate measurements for M2, which is diagnostic. Storer & Tevis (1955:36) state that M2 is almost always under 31 mm in the black bear, but usually at least 31 to 39 mm in the grizzly. Kurte'n & Anderson (1980) report 30 mm as the maximum size for extant black bear and 34 mm in fossils--which is smaller than in most grizzlies. They report The anterior premolars [of a black bear] are normally less reduced than those of U. arctos, and the interorbital width of the skull tends to be greater than that of comparably sized specimens of U. arctos.
They contend that there were no grizzly south of the Alaska-Yukon refugium until retreat of the Pleistocene ice. I do not know whether the upper limit of 31 mm for M2 has been verified for "giant" black bears still living in northeastern North America.
For grizzlies to live east of Hudson's Bay, they would have immigrated either from farther south or from the Alaska-Yukon refugium sometime after retreat of the Pleistocene ice 7500 years ago. There is no evidence, among either living or fossil grizzly, of range expansion from the south into the Northwest Territories, Ontario, or Labrador. But since at least 1900 there has been a gradual dispersal through the Northwest Territories from the Rocky Mountains east toward Hudson's Bay. (Banfield 1958). Banfield considers it unlikely that grizzlies reached Ontario and Labrador ahead of this recent wave of west-to-east dispersal. It is conceivable that an earlier wave occurred, leaving descendants that survived longer east of Hudson's Bay than west of it. However, there is no evidence of this. On the contrary. The arctic ground squirrel Citellus spp., an important fall and spring food for barren ground grizzly bears west of the Bay, does not occur in the Ungava region. So Banfield concludes that the alleged grizzly skins and skulls in Ontario and Labrador were either carried there by Native Americans (as were skins of other animals found only father west), or were actually from the black bear. Although light-colored black bears are now extremely rare east of Minnesota, some existed historically, and one would have expected them to be most common in open habitats with little shade ( 
Ch. 5). So it is feasible that the light-colored Hudson's Bay skins were from "giant" black bears.
Ch. 5). So it is feasible that the light-colored Hudson's Bay skins were from "giant" black bears. The possibility that habitation of tundra is limited by availability of Citellus or comparable rodents should be considered when investigating the apparent scarcity of brown bears on the arctic tundra of Eurasia.
Polar Bear
During the late-Pleistocene, U. arctos gave rise to U. maritimus, the polar bear--an animal specialized for life on the Arctic sea ice, where it hunts seals and scavenges marine mammal carrion during much of the year 
(Fig. 2:12).
(Fig. 2:12). Speciation of the polar bear required isolation from the arctos ancestor. Some isolation came from being out on the sea ice during mating season and eventually from a shift in season--the peak of mating is about 1 month earlier for modern polar bears than for grizzlies (Ch. 12:I.B). Further isolation may have occurred during glaciations (perhaps the Saalian), when advance of ice sheets confined brown-polar bear populations on the coast of Siberia and possibly Alaska. (Kurte'n 1976; Kurte'n & Anderson 1980; Stirling & Guravich 1988).
Kowalska (1969) reports on litters of hybrid cubs produced by mating between a male polar bear and a female brown bear. All cubs were intermediate in lightness of pelage coloration between their parents, but were most similar in head and body shape to the polar bear. This similarity in shape suggests that the corresponding polar bear alleles are dominant over brown bear alleles, something that would have promoted propagation of the polar bear phenotype and facilitated ecological radiation of polar bears into the sea ice habitat. Among offspring of crosses between brown bears and polar bears, daughters and perhaps sons are fertile when back-crossed to pure polar or grizzly/brown bears (Gray 1972).
The polar bear has a circumpolar distribution 
(Fig. 2:13), living mainly on the oceanic pack ice between the shore or shore ice and the permanent ice cap--where seals are most readily caught. (Fig. 1:3). Polar bears range through most of Hudson's Bay (Bremmer 1984). On the Atlantic coast, they once lived as far south as Labrador and possible Maine or even Cap Cod, given that walrus (Odobenus rosmarus) and other pinnipeds were abundant on those beaches until extirpated by technological humans (Lydeckker 1894; Walker 1964).
(Fig. 2:13), living mainly on the oceanic pack ice between the shore or shore ice and the permanent ice cap--where seals are most readily caught. (Fig. 1:3). Polar bears range through most of Hudson's Bay (Bremmer 1984). On the Atlantic coast, they once lived as far south as Labrador and possible Maine or even Cap Cod, given that walrus (Odobenus rosmarus) and other pinnipeds were abundant on those beaches until extirpated by technological humans (Lydeckker 1894; Walker 1964). Sun and Sloth Bears
In addition to Ursus, there are 2 other extant genera of Ursinae--the sun bear Helarctos malayanus and the sloth bear Melursus ursinus. Both sun and sloth bears have long, strongly curved claws. The muzzle and mouth of a sun bear have minor modifications for feeding on ants, termites, and other colonial insects. In the sloth bear, these traits are highly refined. These morphological similarities and adjacent geographic ranges suggest that rather than having arisen separately from Ursavus or Protursus, sun and sloth bears share a more recent common ancestor. Further circumstantial support for this hypothesis will be presented later. Biochemical studies have not yet been done.
Sun bear fossils have been found at Java, Sumatra, and China (Erdbrink 1953). Modern sun bears have occurred in southeast Asia from southern China, south through the Malay Peninsula onto Borneo, Java, and Sumatra; and west to northeast India and southern Nepal where there is overlap with the range of the sloth bear, although the species may not actually share the same habitats. The northern part of sun bear range overlaps the southern portion of Asian black bear range. Much of this area has historically contained tropical rainforest. (Walker 1964; Domico & Newman 1988).
Sloth bear habitat is typically tropical seasonal forest, perhaps adjacent to semi-arid shrubland or grassland. They now live in the forests of Sri Lanka and the Indian subcontinent, ranging as far north as the Great Indian Desert and the foothills of the Himalayas (Walker 1964) where they have had some overlap with Asian black bears and Eurasian brown bears (Fig. 1:3). Kurte'n (1976) reports only 1 known cave fossil for the sloth bear, found in Madreas, India. For further information and photos on these species, click on the following links:
Skulls of sloth and sun bears
Distributions of sloth and sun bears
Sloth bears
Sun bears
Ch. 4a: Ancestral Ursinae & Modern Black Black Bears 
Ch. 4b: Etruscan & Cave Bears Chapter 4. URSINAE (c)