Placental Mammals
There are three types of mammals: monotremes, marsupials and placental mammals. Placental mammals have a placenta in their body, which helps in thee exchange of nutrients and wastes between the mother's blood and that of the fetus. A well-developed placenta in the placental mammals facilitates a longer growth period for the babies in the womb. Marsupials also have an underdeveloped placenta that limits their gestation period.
Origin
In July 1997, researchers discovered the fossils of a new mammal -Maelestes gobiensis- in the Gobi Desert, Mongolia. It was a fairly complete fossil of a shrew- like animal, but slightly bigger in size. This type of structure was a rarity amongst the early mammals. According to researchers, Maelestes was one of the placental mammals that originated around 65 million years ago in the Cretaceous Period, which was characterized by the presence of dinosaurs such as Velociraptor, Oviraptor and Protoceratops.Developed brains
Placental mammals have all the common traits of mammals. Their body temperature is slightly higher than monotremes and marsupials. Placental mammals have the most developed brains in the animal kingdom and they are the most dominant terrestrial vertebrates. They are found almost everywhere and in various sizes. They may range from small scavengers to herbivores pf all sizes or powerful carnivores. Placental mammals include humans, dogs, cats, bears, wolves, beavers, Beluga whales, foxes, bisons and bats.Birth of baby mammals
Placental mammals bear live young that are nourished in the mother's womb before birth. The placenta carries food, oxygen and nourishment from the mother to the child. the young ones of placental mammals are more developed as they are born when they are in an advanced stage. the placenta is made of the same amniotic membrane that surrounds the embryo from the mother's auto-immune system. The immune system is prone to attacking the child considering it to be a foreign body.
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