Like other mammals (apart from the monotremes), marsupials bear live offspring.They are, distinct from all other live-bearers (together described as placental mammals), in that they give birth at a very stage of and nourish the newborn on milk rather placenta.Marsupials are, therefore, classified as infraclass Marsupialia (or Metatheria), while the placental mammals are placed in the infraclass Eutheria.animals such as kangaroos, possums, and bandicoots.The Australasian marsupials, through a lack of competing species, have diversified and become specialized insect-eaters carnivores, and herbivores.In South America, the marsupials are small and mostly arboreal only one species, the Virginia opossum, has spread to North America.
Externally, marsupials are highly varied, although many have long back legs and feet (for example, kangaroos) and elongated snouts, almost all have large eyes and ears. Female marsupials have a unique “doubled” reproductive tract (see below) and in some males the penis is forked The testes are held in a pendulous scrotum with a long, thin stalk, which swings in front of the penis. Apart from their specialized reproductive system, marsupials also differ from placental mammals in that their brain is relativel smaller and lacks a corpus callosum (the nerve tract connecting the two cerebral hemispheres). The group that contains the kangaroos, possums, wombats, and the koala, and the group containing the bandicoots, have an arrangement called syndactyly: the second and third toes of the back foot are combined to forma single digit 2 claws.
Marsupial offspring are born in an almost embryonic state after a very short gestation (only 12 days in some bandicoot species). The newborn makes its way to one of the mother’s nipples, where it remains attached for several weeks. Larger species have single births, but the small quolls and dunnarts have litters of up to 8. In many kangaroo species, the female mates again while pregnant, but the new embryo remains dormant until the previous young leaves the pouch.
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