What are the characteristics of ovipositing, marsupial and placental mammals?

Subclass Characteristic signs Lifestyle
Oviparous, or cloacal Primitive: in the shoulder girdle there are coracoids; eat cesspool; lay eggs. Progressive: hair, mammary glands (however, there are no nipples, ducts of glands open on the “milky” field of the mother’s skin, the cubs lick it). Body temperature is low (25-30 ° C), largely depends on the temperature of the environment The platypus lives along the shores of water bodies, swims and dives well, feeds on aquatic invertebrates (insects, crustaceans, mollusks, worms). Cubs have milk teeth, in adults, the jaws are toothless, flat. On the legs there are membranes and claws. Eggs with a diameter of 15-20 mm, in a parchment-like shell, lay in a hole, incubate for 7-10 days
Marsupials Primitive: the placenta is underdeveloped, the gestation period is very short, characterized by the presence of a bag on the abdomen, in which the development of the cubs ends. Progressive: live birth; mammary glands with nipples, coracoids fuse with the shoulder blades. Body temperature is about 36 ° C. Teeth do not change (correspond to the milk teeth of higher mammals) There are insectivores (marsupials, moles), carnivores (marsupials, marten), herbivores (kangaroos, marsupial bear – koala)
Higher, or placental The embryo develops in the uterus, where, due to the fusion of two amniotic membranes, a placenta is formed, forming a spongy chorion; chorionic villi fuse with the uterine epithelium; give birth to formed cubs that are able to independently feed on breast milk. There are milk and permanent teeth There are insectivores, carnivores, herbivores; a total of 17 orders (the main ones are insectivorous, bats, rodents, lagomorphs, carnivores, pinnipeds, cetaceans, artiodactyls, artiodactyls, proboscis, primates)
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