- Related Topics:
- echidna
- platypus
- Ornithorhynchidae
- Steropodontidae
- Kollikodontidae
monotreme
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What is a monotreme?
Monotremes are mammals belonging to the order Monotremata. They are an ancient group of mammals characterized by the fact that they lay eggs. The order includes the platypus and echidnas that are native to Australia, Tasmania, and New Guinea. Monotremes have a combination of primitive and specialized traits, making it difficult to determine their relationship to other mammal groups. The name Monotremata refers to the single opening, or cloaca, that both sexes have for reproduction and excretion.
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What makes monotremes different from other mammals?
Monotremes stand out as the most ancient order of mammals because they lay eggs, a trait not shared by other living mammals. They also have primitive skeletal features, such as the shoulder girdle and skull characteristics, that have been lost in other mammals. The name Monotremata means "one-holed," referring to their single opening for reproduction and excretion.
Unlike placental mammals and marsupials, monotremes exhibit a puzzling combination of primitive features and specialized characteristics. The platypus is a semiaquatic carnivore-insectivore, while echidnas have a specialized diet of small invertebrates.
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How do monotremes reproduce?
Monotremes, the most ancient order of mammals, have a unique reproductive strategy. Unlike most mammals, they are oviparous, meaning they lay shelled eggs similar to those of reptiles and birds. After the egg is laid, incubation occurs where the egg is maintained at a uniform temperature. Young monotremes hatch at an early stage of development and rely on parental care. Both sexes have a single opening, called a cloaca, for both reproduction and excretion. The ovarian cycle in monotremes is similar to that of other mammals. They reach sexual maturity at about one year.
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What are the main species of monotremes alive today?
Today, the main species of monotremes include the platypus (Ornithorhynchus anatinus) and the echidnas (family Tachyglossidae). There are four species of echidna that can be found in Australia, Tasmania, and New Guinea. Monotremes are an ancient group of mammals that lay eggs instead of giving birth to live young. They have a single opening at the rear of their bodies for reproduction and excretion. Platypuses are semiaquatic carnivores-insectivores, while echidnas are land-dwelling insectivores.
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Where do monotremes live and what habitats do they prefer?
Monotremes are an ancient order of mammals that includes the platypus and echidna. These egg-laying mammals are native to Australia, Tasmania, and New Guinea.
Platypuses are generally solitary and semiaquatic, living near rivers, streams, and lakes. They create burrows in the banks for resting. They can be found in habitats ranging from the high country of Tasmania and the Australian Alps to lowland areas close to the sea.
Echidnas live in Australia and New Guinea in varied habitats where they can find shelter and food, such as hollow logs, underbrush, and caves. They are widely distributed across Australia.
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How do monotremes care for their young and get food?
Monotremes, the most ancient order of mammals, nourish their young with advanced parental care. Young monotremes hatch at an early stage and depend on their parents. Platypuses are energetic feeders, foraging for larval insects and freshwater crustaceans, detecting prey through electromechanical systems. Echidnas have a specialized diet of small invertebrates like ants, termites, and worms, which they locate with electroreceptors in their beaks. Both echidnas and platypuses use electroreceptors to find food.
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monotreme, (order Monotremata), any member of the egg-laying mammalian order Monotremata, which includes the amphibious platypus (family Ornithorhynchidae) and the terrestrial echidnas (family Tachyglossidae) of continental Australia, the Australian island state of Tasmania, and the island of New Guinea.
Natural history
Monotremata is the most ancient living order of mammals. In addition to being egg layers (oviparous), members of this order share primitive skeletal features such as the shoulder girdle and skull characteristics that have been lost in other living mammals. Relationships to other mammalian groups have been difficult to determine because of the puzzling combination of primitive features and specialized characteristics, a phenomenon known as mosaic evolution. Certain features of the skull appear to link monotremes to the extinct early mammal groups. Other evidence, particularly genetic data, places Monotremata close to more-advanced mammals, namely marsupials.
Monotremes are very highly modified for their particular ecological niches. The platypus is a semiaquatic carnivore-insectivore, and the echidnas have a specialized diet of small invertebrates such as ants, termites, and worms. The name Monotremata means “one-holed,” in reference to the fact that both sexes have only one opening at the rear of the body, which is used for both reproduction and excretion.
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Paleontology and classification
Various mammals of the Mesozoic Era (251 to 65.5 million years ago) with more-advanced shoulder girdles (including a multituberculate) have recently been discovered, indicating that the monotreme shoulder girdle developed before the shoulder girdles of some other mammalian groups. None of the theories of monotreme relationships has been universally accepted, although the subject is of great interest to scientists who study mammalian evolution.
Included within the monotreme order are two families known only from early in the Cretaceous Period (145.5 to 65.5 million years ago) in Australia: the platypus-like Steropodontidae, represented by a single species (Steropodon galmani), and the uniquely specialized Kollikodontidae, which is also represented by a single species (Kollikodon ritchiei). Both are known only from opalized jaw fragments. The strange rounded cusps on the molar teeth of K. ritchiei were a surprise to paleontologists, suggesting that Cretaceous monotremes may have been more diverse and widespread than previously thought and may in fact have been the dominant mammals in the Australian sector of the ancient supercontinent of Gondwanaland. The Cretaceous discoveries bring the number of families within the order to four.
The oldest fossil platypus is recorded from the Paleogene Period (65.5 to 23 million years ago) of South America, providing evidence that during this time platypuses were distributed from Australia through Antarctica to South America.
Although the fossil record extends back to the early Cretaceous, origins of the group undoubtedly lie much farther back in time. Anatomic evidence such as the shoulder girdle suggests an origin perhaps as long ago as the middle of the Jurassic Period (199.6 to 145.5 million years ago).
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Many researchers agree that the primitive features in monotremes reflect an ancient origin. Any attempt to determine the relationships of monotremes must take into account these primitive retentions. This is problematic in that either these archaic features reflect an origin far removed from that of living placental and marsupial mammals or else a mechanism must be found to explain how these features could be possessed by a group that is closely related to mammals without these traits.
- Order Monotremata
- 5 species in 2 families.
- Family Tachyglossidae (echidnas)
- 4 species in 2 genera from Australia, Tasmania, and New Guinea.
- Family Ornithorhynchidae (platypus)
- 1 Australian species.