Large species of carnivorous mammals are the most vulnerable species in an ecosystem. At strong (though and convertible) fluctuations of number of prey number of predators can fall down to critical level, and the species appears at the edge of extinction. Development of extensive territories of land by people, and the destruction of habitats followed it had strongly reduced number of large predators, and they had not gone through ecological crisis at the boundary of Holocene and Neocene.

After extinction of mankind efficiency of ecosystems began to restore. Numerous descendants of small species, mainly rodents and lagomorphs had occupied the place of large herbivores exterminated by people and had become extinct because of natural reasons. After herbivores, some predators also had strongly increased in size. Among large predators the serious application for domination in fauna had been made by representatives of mustelid family. In temperate and partly in subtropical zone of Northern hemisphere their representative, berl, is found. It is a huge carnivorous species of mustelids, the analogue of fossil marten Perunium, and the descendant of ferret (Mustela putorius). Its ancestors, probably, took in ecosystems a place similar to wolverine (Gulo gulo), and any of their species had managed to enter large-sized class. This attempt appeared extremely successful. Berl is massive and sluggish species of mustelids, in size compared to bear (hence the name: “berl” is the ancient Slavic name of bear). The height of adult animal at a shoulder exceeds one meter, length of body without tail is up to three meters; weight is over 400 kgs. The adult animal, as against bears, hardly swarms up trees (cubs, on the contrary, do it very dexterously). By constitution berl resembles polar bear (Ursus maritimus) of human epoch – it has rather small head on strong neck, large trunk and muscled paws. As against bears, berl has long fluffy tail. It is solitary and aggressive species of mammals, and by position of tail each individual expresses the mood, not entering close contact to relatives. Fur of berl is rich, especially in winter. Summer colouring of wool of animal varies from dark grey up to beige, straw-colored and even black. Usually lighter-colored individuals live at the south of area, and darker ones – in forests of temperate zone. These animals are able to change color of wool to winter. Individuals from cold areas become snow-white in winter, and in more southern areas winter fur of animal turns grayish. Individuals from southern borders of area are almost unable to change color of winter wool – it becomes thicker and only a little lighter. In winter berl keeps activity even in ringing frosts. Holocene bears were omnivorous and even mainly herbivorous ones (except for polar bear). Berl is an exclusive predator. Using huge physical strength, it attacks large mammals, making the basis of its diet: in Eurasia obda, aurochid, nozdrokh, shurga, in North America giant wood porcupine, in Greenland  and . Berl can not chase its prey, therefore it uses another tactics – it pursues herd of herbivores during the long time while the weakest animal will keep abreast. When prey appears far enough from relatives, berl rushes on it and kills by impact of paw – it simply brings down animal on the ground and breaks its neck. Hunting takes a lot of time and forces, therefore berl aspires to use food resources maximum full. This predator stays near killed prey for a long time: in summer while meat will start to spoil, and in cold season while on carcass there is at least something edible. Also berl willingly eats carrion, or takes by force prey of smaller predators. This predator is solitary animal; each individual has extensive fodder territory. Berl marks borders of territory by unpleasantly smelling liquid which is secreting from anal glands. The animal leaves marks on stones and trunks of trees. In courtship season (in the beginning of autumn) males wander on territories of females, and couple with them. Only at this time females become more tolerant to presence of adult relatives in their territory. At the end of spring when it becomes warm enough, the female arranges in forest carefully disguised den in which brings posterity: two – three blind and helpless cubs. The posterity develops rather slowly: only at bi-monthly age cubs start to leave den and to explore the world around. They spend a lot of time in games – swarm up trees, combat and simulate hunting, “attacking” on trunks of trees fallen on the ground. In autumn the posterity finally abandons shelter, and studies to hunt. Young animals keep in common with the female during all next year and all this time demand attention from the part of mother. Therefore the female of berl brings posterity only once in two years. Berl is widely settled in Eurasia and at the north of North America. It lives mainly in areas of coniferous and deciduous forests, forming a number of subspecies. At the territory of Siberia and Far East very large nominative subspecies great, or Siberian berl (Quasiursus asiaticus asiaticus) is found. At this subspecies there is the darkest summer colouring of fur, and winter fur is greyish-white. At the north of Europe it is replaced by smaller European subspecies, mechka(Quasiursus asiaticus occidentaliswhich has the smaller size and reddish or yellowish colouring of summer fur. The north of Eurasia and North America is occupied by indistinctly separated from these forms subspecies oshkooy** berl (Quasiursus asiaticus leucoswith snow-white winter and dark grey summer fur. This animal lives in woods of Far North, often hunts and gathers carrion at the coast of Arctic Ocean, and migrates on ice to northern islands in winter. At the south of area this kind forms hybrid forms with European and Asian subspecies. At the territory of North America the Asian berl is replaced by two close species.

Mountain berl, or ueb (Quasiursus montanophilus) lives in woods of Rocky Mountains ridges, coming along high-mountainous areas far to the south (up to territory of Mexico). This species dark grey summer fur, often with white spots on lower jaw and breast; at some individuals there is white stomach. This species is only a little smaller than Siberian berl, especially the representatives of northern populations distinguished by shaggy rich fur. Winter fur at this species is bluish-grey. Ueb differs from Asian berl in larger head and more flat teeth – it is appreciably less selective in food. In summer this animal often eats vegetative forage – mushrooms and berries.

Quas mon
Eastern berl (Quasiursus appalachensis) is much smaller than its western relative, and is approximately equal in the size to European mechka. It is colored yellowish-brown color and keeps such color of wool the year round. This species differs in lightest constitution among the relatives, and swarms up trees much better. It occupies evergreen and semi-deciduous forests of the eastern part of North America.

In Eastern Asia there is one more species of this genus - tiny berl (Quasiursus minimus). This animal is the analogue of wolverine, medium-sized carnivorous species (its growth at a shoulder is no more than half meter). It inhabits forests of various types, woodlands and mountain forests, and also boggy woods in river valleys. This animal eats various mammals, large birds and fish. It is able to climb on trees, to swim and to dive. The skin of tiny berl has pale-yellow color, and paws are dark brown; on muzzle there is dark “mask”.

Red berl (Quasiursus rufus) living in Japan is close to this species. It is larger, than tiny berl (growth at a shoulder is about 60 cm), more thickset and strong combined. At this animal there is rich rusty red fur and wide feet – it feels well in high mountains and easily moves on snow, not failing down. Red berl lives in northern part and mountain areas of Japan Islands, preferring woody districts and thickets of bamboo. It also is a predator, and prefers to hunt mammals.