monotreme


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Related to monotreme: placental mammal

monotreme

(mŏn`ətrēm'), name for members of the primitive mammalian order Monotremata, found in Australia, Tasmania, and New Guinea. The only members of this order are the platypusplatypus
, semiaquatic egg-laying mammal, Ornithorhynchus anatinus, of Tasmania and E Australia. Also called duckbill, or duckbilled platypus, it belongs to the order Monotremata (see monotreme), the most primitive group of living mammals.
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, or duckbilled platypus, and the several species of echidnaechidna
or spiny anteater,
animal of the order Monotremata, the egg-laying mammals. A short-legged, grayish brown animal, the echidna is covered with sharp quills and can protect itself by rolling into a tight bristly ball. It may reach 18 in. (46 cm) in length.
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, or spiny anteater. Although monotremes possess the distinguishing mammalian features of hair and mammary glands, they are unique among mammalsmammal,
an animal of the highest class of vertebrates, the Mammalia. The female has mammary glands, which secrete milk for the nourishment of the young after birth. In the majority of mammals the body is partially or wholly covered with hair; the heart has four chambers, and
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 in laying eggs rather than giving birth to live young. The eggs are like those of reptiles, with large yolks and leathery shells. Like birds and reptiles, monotremes have a single opening, the cloacacloaca
, in biology, enlarged posterior end of the digestive tract of some animals. The cloaca, from the Latin word for sewer, is a single chamber into which pass solid and liquid waste materials as well as the products of the reproductive organs, the gametes.
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, for the passage of liquid and solid wastes, the transfer of sperm, and, in the female, the laying of eggs. In addition, certain features of the skeletal structure are like those of reptiles, and the regulation of body temperature is less effective than in other mammals. Adult monotremes are toothless. The males possess spurs on their hind feet; these are connected to poison glands and are presumably used as weapons. Mammals are known to have evolved from reptiles; the monotremes probably branched off at an early stage of mammalian evolution and have retained many reptilian features. They are classified in the phylum ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
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, subphylum Vertebrata, class Mammalia, order Monotremata.
References in periodicals archive ?
Australia has some of the strangest animals on Earth It is the only continent to have all three groups of mammals - placentals, marsupials, and monotremes.
The platypus belongs to a very small group of mammals called the monotremes.
The configuration of these ear bones is similar in all three extant groups of mammals: the placental mammals, which bear live young, the pouched marsupials, and the egg-laying monotremes, such as the duck-billed platypus.
The world's only other monotreme is the echidna, or spiny anteater, which is also native to Australia.
According to a report by ABC News, the finding contradicts the widely held view that monotremes, or egg-laying mammals, are "living fossils" that have not evolved.
Lead author PhD candidate Rebecca Pian said that the monotremes (platypuses and echidnas) are the last remnant of an ancient radiation of mammals unique to the southern continents.
Krosoczka is moving from lunch ladies to monotremes, and he will introduce his latest characters to children and adults this evening at the Worcester Public Library as part of the summer reading kickoff and Reading in Our City Week.
Although the continent accounts for a little less than 6 per cent of the planet's landmass it supports 12 per cent of the world's bird species, 10 per cent of the reptiles, 9 per cent of all frogs, and 6 per cent of mammals (but many are unique with 50 per cent of monotremes and 66 per cent of all marsupials found exclusively in Australia) (Page & Baxter, 2006).
That is, the common passage by which alimentary and urinary excretion occurs in birds, reptiles, fish and monotremes (egg-laying mammals).
But the platypus also lays eggs - one of only two mammals, known as monotremes, to do so.