Steppe ecosystems of Eurasia before the beginning of the vigorous human activity had not conceded to savannas of Africa in biological efficiency. Various hoofed mammals – aurochses, wild horses and antelopes – had been dominant species of steppe herbivores. People ploughed steppes, transforming these areas into primitive agrocenoses, and exterminated steppe animals. The result of human activity was a degrading of steppe ecosystems by the end of human era. In Neocene the population of newly appearing ecosystems had been formed, actually, from zero. In the Euroasian steppes of temperate climatic zone representatives of new groups of herbivorous mammals dominate – , cursorial boar relatives, gracile , and some other forms of herbivores. Among new steppe herbivores of Neocene large representatives of rodents took the important place. In Neocene rodents represent one of the most successful orders of mammals.
Jerboas were the characteristic group of rodents of the Old World lived in open spaces. In ice age at the boundary of Holocene and Neocene, in conditions of desertification and deforestation, some representatives of jerboa family had got a wide distribution and had considerably increased in size. This adaptation, favourable in conditions of cold climate, has allowed one species of these rodents to occupy an ecological niche of the analogue of small antelopes in steppes of Eurasia. This animal is giant kangaroo jerboa, a gregarious middle-sized mammal. This rodent has kept features of anatomy, characteristic for family representatives, adjusted for the giant size: the animal weighs up to 15 kg. In behaviour and a habit of movement giant kangaroo jerboa is similar to small kangaroos like wallaby. The body length of this animal reaches 60 cm, and tail is about one meter long. Long strong tail at this rodent serves for support when animal eats, bringing food to the mouth by forepaws. Giant kangaroo jerboa moves almost exclusively on rear legs, accelerating momentum up to 70 kms per hour In case of danger it makes jumps up to 6 meters long. At jumps tail of animal serves as the balance weight. On the tip of tail the switch of white hair is advanced. Ears of giant kangaroo jerboa are rather short and rounded. This animal does not dig holes, and does not run into hibernation in winter – these changes of behaviour are consequences of increase of body size. In winter this animal keeps activity, and it does not need overcooling. Summer wool of giant kangaroo jerboa has sand yellow color with small dark spots merging to short cross strokes on back. In winter the wool of animal turns lighter in color and becomes thicker. At this species of rodents wool is weakly attached to skin. If the predator will seize this animal, wool easily drops out and allows the animal to escape from its teeth. Moreover in winter “dress” at giant kangaroo jerboa “ski” grow on feet – it is a border of rigid wool. This adaptation helps an animal to jump easily on snow, not falling in. In summer giant kangaroo jerboa is a solitary animal. Each individual has territory, and its borders are marked by urine and secretions of smell glands. The centre of territory is a hole or any other ready shelter. Giant kangaroo jerboa is not able to dig a hole itself, therefore it uses ready shelter – usually holes dug out by , huge local rodent. Usually the territory with a hole is occupied by female. Males are not so choosy in the choice of shelter: rich bushes as shelter are frequently enough for them. This species of rodents has rather long pregnancy time, and the female brings only one litter in one year, in which there are about 5 cubs. Newborn cubs are helpless and female hides them in hole, closing an entrance with a bunch of prickly grass or bush pulled out from the ground. Cubs are born in the beginning of summer, and within the first month of life they do not leave shelter. The female watches the vicinities of shelter, and if necessary it is ready to distract a predator in order to withdraw it far away from shelter. Cubs behave very cautiously, even having learned to move. While the female is near to posterity, cubs can leave a hole and play, but at a first sign of danger they hide in. The posterity leaves a hole for ever at the age of about one and a half months. At this time colouring of cubs is cross-striped, that helps them to mask in grass better. It is the only protection of young animal. Usually young animals wait for returning of the female, having hidden in grass. In case of need cubs can escape from the enemy, quickly jumping and sharply changing direction of movement. When danger passes, they come back to a former place, waiting for the female returning. At the same time young animals begin to eat plants. At the end of summer the litter is fed in territory of the female, gaining weight. Young animals become independent to an autumn, having reached the weight of 8 – 9 kg. This is a very important time in their life: the young animal, not having accumulated a sufficient stock of hypodermic fat, easily becomes a victim of frost. In the first winter about a half of the young growth born in summer perishes because of various reasons. But the next year in autumn females become capable to pairing, and at the age of two years, after the second wintering in their life, they bring posterity the first time. In winter, when it is more difficult to find food and danger of predator attacks is more probable, giant kangaroo jerboas gather to herds numbering over fifty animals, and wander on extensive territory. In spring, when snow thaws, the common territory of herd is broken into individual sites, and animals become solitary ones again.