Marsupials: what they are, types, characteristics and examples

Marsupials are a group of very primitive non-placental mammalian animals, characterized by incomplete embryonic development within the mother. The babies that are born viviparously, that is, inside the mother, come out after a certain time and even without finishing their formation, to finish their development outside the uterus.

Marsupials are important animals in evolution, because they represent the link between oviparous animals, which develop outside the mother, with viviparous animals.

Marsupials can be divided into two large groups according to their continental origin: Australian marsupials and American marsupials. Each type has certain species, which are not found in its opposite group. Let’s review them below.

Australian marsupials

70% of marsupials are found in Australia, so it could be thought that they originated there, but the story is actually different. By phylogenetic analysis it was determined that a single species of American marsupial, the mountain monkey Dromiciops gliroidesarrived unintentionally sailing on rafts across the water to Australia, when this land mass was just separating from the supercontinent called Gondwana. This single American species was the one that gave rise to the great diversity of Australian marsupials that we know today.

These Australian marsupials have a diversified diet, which includes herbivores in addition to carnivores and omnivores, which, together with the lack of competition from other mammals, allowed them to dominate the continent over placental mammals. That is, the most common mammals in Australia are marsupials and not placental mammals.

American marsupials

They are also known as New World marsupials. They first originated in North America, and went down to South America through the Isthmus of Panama when it was formed. Today they are more abundant in the southern part of the continent than in the north, where only one species exists. They are mainly carnivores and omnivores, but there are no herbivores. They are not as abundant on their continent, due to competition with placental mammals.

We can find certain common characteristics in marsupials, which are:

• Presence of hair.
• Temperature regulated by themselves.
• Presence of mammary glands.
• Small skull.
• They do not have a corpus callosum in the brain.
• They have epipubic bones that serve to provide support, and which are not present in most mammals.
• Females have two vaginas and two uteruses, which join into a canal when they give birth.
• They do not develop a true placenta.
• Males have two penises.
• The gestation is very short.
• They have the pouch, which is the most important characteristic of these animals.

What is the marsupium

The marsupium is a small bag that is in the external abdomen of the female, inside which the baby will be kept after leaving the uterus to finish its development there. There are some cases where the pouch is located on the back, but they are the least. It is the most important characteristic of marsupials, which gives the group its name.

This pouch gives them protection, warmth and food, because inside the pouch are the mother’s nipples from which she will breastfeed. In most marsupials this structure is always present, but there are some cases where it only appears when it is time to gestate.

red kangaroo (Macropus rufus)

Kangaroos are the most iconic animals in Australia, as an example of the importance of marsupials on the island. The red kangaroo is the largest species of kangaroo, standing 1.8 meters tall. They move only by jumping, which does not pose any problem to them because they have large legs adapted to this. They are herbivores, and as their name indicates, their fur is brown with a reddish tint.

Golden bandicoot (Isoodon auratus)

Bandicoots, called bandicoots in English and sometimes used as such in Spanish, are marsupials similar to a rat, but larger. They have burrowing habits, and they stand out because they have the marsupium on their back.

This species differs because it has a relatively short snout compared to other bandicoots. Its fur is golden, and it measures 30 centimeters long. It lives mainly in arid areas, but can also live in more wooded areas. It is vulnerable to disappearing since the colonization of Australia, and today its distribution is limited to the far north.

Tlacuache (Didelphis virginiana)

It is the only marsupial that lives in Mexico and the United States. It is distributed to Central America, with Costa Rica as the limit. It is characterized by having a long hairy tail, which in Mexican tradition is said to have been because it brought fire in it to humanity. Their size is similar to that of a cat, and they have gray fur with a black face. They are nocturnal and omnivorous, so it is common for them to be found in cities. When they feel threatened they play dead to avoid being attacked.

Mountain monkey (Dromiciops gliroides)

Despite its common name, it should be noted that it is not exactly a monkey. Its size is very small, about 20 centimeters. Its habits are arboreal, holding on to it with the help of its prehensile tail to look for insects and fruits to feed on.

Despite its small size, this is the ancestor of the large kangaroos. It is the little monkey that we mentioned previously, which gave rise to the diversification of Australian species, to the point that it is genetically more related to Australian marsupials than to American ones. Today it only exists in its native place of origin: Chile and Argentina.

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