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  • The order of Monotremes (protothere) is considered the most primitive among modern mammals. It has the name “one-pass” because animals’ urogenital sinus and intestines fall into the cloaca, and do not go out through separate passes. They inherited several features from reptiles: egg laying, coracoid bone, which is a well-developed, do not joint with a scapula, joint of some details of the skull bones, the development of marsupial bones and so on.

    The Monotremes are distinguished from marsupials and other mammals that have a coracoid bone as a simple apophysis of scapula, by the complete presence of coracoid bone. Other characteristics related to mammals such as mammary glands and hair, are rather primitive in monotremes and resemble by structure the sweat glands.

    Many features similar monotremes and birds are adaptive rather than genetic. And monotremes’ possibility to lay eggs makes them more close to reptiles than to birds. But unlike birds, monotremes’ egg yolk is less developed. Cornified eggshell consists of keratin and is very similar to reptiles’ eggshells.

    Such structural features as the reduction of the right ovary, the presence of pockets in the gastrointestinal tract, similar to birds struma and the absence external ear strongly resemble birds. But these similarities are more adaptive, not giving the right to speak about the relationship of birds and monotremes. Adult protothere do not obtain teeth.

    As for body temperature of monotremes, they stay at intermediate position between reptiles (poikilotherm) and true homoithermic animals (birds and mammals). Moreover, their body temperature varies depending on the ambient temperature.

    Currently, the order of Monotremes has 3 alive representatives that belong to two families: the platypus and echidnas, the last one includes two species of echidnas – spiny anteaters (Australian echidna) and Bruijn’s echidna. Their habitat is only Australia, Tasmania and New Guinea.



    Long-beaked echidna