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Most mammals are viviparous, giving birth to live young. [1] However, the five species of monotreme, the platypuses and the echidnas, lay eggs. The monotremes have a sex determination system different from that of most other mammals. [2] In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian ...
The class Mammalia is divided into two subclasses based on reproductive techniques: monotremes, which lay eggs, and therians, mammals which give live birth, which has two infraclasses: marsupials/metatherians and placentals/eutherians. See List of monotremes and marsupials, and for the clades and families, see Mammal classification ...
All modern mammals give birth to live young, except the five species of monotremes, which lay eggs. The most species-rich group is the viviparous placental mammals, so named for the temporary organ used by offspring to draw nutrition from the mother during gestation.
Lions may live 12–17 years in the wild. [45] Although adult lions have no natural predators, evidence suggests most die violently from attacks by humans or other lions. [174] Lions often inflict serious injuries on members of other prides they encounter in territorial disputes or members of the home pride when fighting at a kill. [175]
These three layers give rise to all the various types of tissue in the body. The endoderm later forms the lining of the tongue , digestive tract , lungs , bladder and several glands . The mesoderm forms muscle , bone , and lymph tissue, as well as the interior of the lungs, heart , and reproductive and excretory systems .
A litter is the live birth of multiple offspring at one time in animals from the same mother and usually from one set of parents, particularly from three to eight offspring. The word is most often used for the offspring of mammals , but can be used for any animal that gives birth to multiple young.
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Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop inside eggs that remain in the mother's body until they are ready to hatch.