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Astrorhy

Climatic changes in Neocene favour to evolution of thermophilic and moistureloving species. The most part of territory of Australia in Holocene was covered by droughty deserts. In Neocene this continent had moved to the north and had joined to New Guinea forming unite continent Meganesia. Rivers supplying with water plains of the central part of Meganesia spring from the north and east of the continent. The Eastern Meganesia prospers due to large river system occupying the territory of former Murray River. It runs into extensive shallow-water Eyre Gulf filled with warmed up brackish water. Expansion of habitats stimulated the evolution of water inhabitants. The genealogical branch of monotremes declined till the Cenozoic Era had received new opportunities in Neocene. The occurrence of productive ecosystems has allowed to evolve to the various specialized species of these primitive mammal. The large piscivorous duck-bill mergotherium (Mergotherium piscivorus) inhabits rivers, and in mountain streams its tiny aggressive relative ancistrotherium (Ancistrotherium radulus) lives. In lower reaches of rivers running into Eyre Gulf, and also at small Flinders Island, one more descendant of duck-bill, the starbill, lives. This species of duck-bills resembles the American star-nosed mole in many respects – it leads similar way of life, and even has few common features in appearance. This is small (rat-sized) animal with powerful forepaws using for digging. Between toes membranes are advanced; the animal is nice swimmer. At this animal the swimming membrane on forepaws is reduced, and they are more adapted to digging, than forepaws of duck-bill. During the swimming starbill presses them to the body. Besides the starbill is able to climb on roots in mangrove thickets, and often catches ground insects and snails. The tail at starbill is weak and short – this animal swims with the help of strong hind paws. The most original part of appearance of starbill is its beak, the family feature of duck-bills. Beak at this species is toothless, short and wide. But on it the set of sensitive leathery outgrowths grows; that’s why the beak of starbill resembles a little the snout of star-nosed mole (hence the name: Condylura – the American star-nosed mole). This animal is protected from predators by poisonous spurs (it is one more feature inherited from duck-bill) colored bright orange. At males spurs are longer, than at females. Fur of animal is black or dark brown with contrast white marks on head and shoulders. The predator attacking starbill will remember its colouring, having received a painful prick of poisonous spurs. Starbill lives in damp ground of riverbanks and in marshlands. By this feature it also resembles its prototype from the insectivores order. It eats various ground and water invertebrates – earthworms, leeches, snails and larvae of insects. The animal searches for them with the help of sensitive outgrowths on edges of beak. These outgrowths are rich in chemo- and electroreceptors, and permits to define presence of live creatures even in darkness. Under water the starbill closes eyes, and is guided exclusively with the help of touch sence and receptors of beak. Starbill is a solitary animal. Each individual digs complex system of tunnels in riverbank. The nest for posterity rearing represents the long hole terminating in the nesting chamber. This chamber is located above maximum water level, and has an emergency exit. In lower reaches of rivers starbills of different genders lodge in different places. Males prefer to live in territories completely filling with water during the inflow. Here the amount of forage is more, and for spending the night animal often uses any casual shelter. Females prefer to settle closer to riverbanks where their long-term holes will not be filled with inflow. At Flinders Island the separate population of this species differing in smaller sizes (animals weigh approximately 20% smaller, than their relatives from the “motherland”) lives. Conditions of life at this island are more severe, than at the continent – permanent sources of fresh water are not present there. Therefore starbills of Flinders Island receive necessary moisture exclusively from food. Also at these animals there is stronger poison secreting in smaller amount.

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