What are the types of mammals?



There are more than 5,000 different types of mammal in the world today. They are divided into three groups, based on how their babies are born and raised.



Egg-laying mammals



Monotremes are the only mammals to lay eggs. The monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts compared to the more common mammalian types. In addition they lay eggs rather than bear live young, but like all mammals, the female monotremes nurse their young with milk. Echidnas, or spiny anteaters, and the duck-billed platypus from Australia are the two types of monotremes alive today. The first things you probably notice about an echidna are the spines that cover most of its body, except for its face and belly. The animal also has short fur in between its spines, as well as on its underside. The spines are a great protection against predators. When the echidna wedges itself in a hole or rolls up in a ball, it's almost impossible to attack this living pincushion!



The echidna's long front claws might look scary too, but they're more useful in digging than in protection.



There are two types of echidnas, short-beaked and long-beaked. The short-beaked is much smaller than its cousin, weighing from five to 15 lbs., with a length of 12 to 18 inches.



Pouched mammals



Marsupials are mammals that carry their babies in a pouch to keep them safe. Australia is home to many marsupials, including kangaroos and koalas. They are notable because they have pouches in which they place their young when they are born. This pouch is near the mammary glands so the mother can nurse the young animals. When they are big enough, they leave the pouch and are on their own. They give live birth, but they do not have long gestation times like placental mammals. Instead, they give birth very early and the young animal, essentially a helpless embryo, climbs from the mother's birth canal to the nipples. There it grabs on with its mouth and continues to develop, often for weeks or months depending on the species. 



Placental mammals



Placental mammals, such as pigs, give birth to babies that are more developed than marsupial babies. This is the largest group of mammals and includes humans. The placentals include all living mammals except marsupials and monotremes. Although some authorities consider the marsupials (cohort Marsupialia) to be placental mammals, these animals have a less-developed, less-efficient type of placenta that limits the gestation period. The true placenta of the placentals allows for a longer developmental period within the protection of the womb, a factor considered to have contributed to the evolutionary success of the group. Fossil evidence shows that the first placental mammals evolved between about 163 million and 157 million years ago during the Jurassic Period (201.3 million to about 145 million years ago).



 



Picture Credit : Google


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