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Monotremes are mammals that are best known for laying eggs, instead of giving birth to their young like marsupials and eutheria?s. |
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Monotremes are mammals that are best known for laying eggs, instead of giving birth to live young like marsupials and [placental mammals]? (eutheria?). |
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The word monotreme comes from the Greek words mono- and trema, meaning one and hole. The one hole refers to the fact that monotremes have a single opening for the urinary, digestive and reproductive organs. |
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The word monotreme comes from the Greek words mono- and trema, meaning one and hole. This name refers to the fact that monotremes have a single opening for the urinary, digestive and reproductive organs. |
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Living monotremes lack teeth as adults. Fossil forms and the young of living monotremes have the "tribosphenic" molars which are one of the hallmarks of mammals. However recent work suggests that that monotremes acquired this form of molar independently of placental mammals and marsupials. [1] The jaw of monotremes is constructed somewhat differently from other mammals, and the jaw opening muscle is different. Like all true mammals, the tiny bones that conduct sound to the inner ear are fully incorporated into the skull, rather than lying in the jaw as in cynodonts and other pre-mammalian synapsids. However, the external opening of the ear still lies at the base of the jaw. The monotremes also have extra bones in the shoulder girdle, including an interclavicle, which are not found in other mammals. The monotreme leg bears a spur in the ankle region. |
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Living monotremes lack teeth as adults. Fossil forms and the young of living monotremes have the "tribosphenic" molars which are one of the hallmarks of mammals. However, recent work suggests that monotremes acquired this form of molar independently of placental mammals and marsupials. [1] The jaw of monotremes is constructed somewhat differently from that of other mammals, and the jaw opening muscle is different. As in all true mammals, the tiny bones that conduct sound to the inner ear are fully incorporated into the skull, rather than lying in the jaw as in cynodonts and other pre-mammalian synapsid?s. However, the external opening of the ear still lies at the base of the jaw. The monotremes also have extra bones in the shoulder girdle, including an interclavicle, which are not found in other mammals. The monotreme leg bears a spur in the ankle region. |
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