It is common in science to group animals according to certain characteristics in order to facilitate the work of classifying and studying them. One of these characteristics is reproduction, according to which animals are classified into oviparous (animals that lay eggs), viviparous (the young develop inside the mother) and, as an intermediate form of reproduction between these two, the ovoviviparous (they develop eggs inside the mother). In the case of mammals we can see very curious cases. Therefore, in this article by Ecologista Verde we wonder if mammalian animals are oviparous or viviparous and we respond by explaining this and many more details.
Are mammalian animals oviparous or viviparous? - here the answer
As we have mentioned before, within mammals there are cases that can be considered the exception to the rule. In fact, the basics is that mammalian animals are viviparous, since the vast majority are, but there is a small group that are oviparous mammalian animals, that is, they lay eggs and hatch from them after incubation.
Therefore, the most correct answer to the question of whether mammalian animals are oviparous or viviparous is that are of both types of reproduction, mostly of the second mentioned form and in very specific cases of the first. Below we explain all this in more detail and with examples.
Mammalian animals that are oviparous
The oviparism It is an ancestral and little evolved characteristic within the methods of reproduction, so mammals are mainly viviparousThey are more evolved animals than the rest and have evolved in the form of reproduction. The only exception to this is the group of the monotremes, which include platypus species and the echidna family. Monotremes represent a group of very primitive mammals and that they still maintain certain reptilian characteristics.
Between the characteristics of oviparous mammalian animals is it so:
- They do not have breasts or nipples (their young feed through the pores of their mothers' skin).
- They are practically blind and deaf, although they have eyes and ears. They have electroreceptors in their snouts.
- They only inhabit Tasmania, New Guinea and Australia.
- They are capable of living in captivity for up to 50 years.
- Male platypuses can be poisonous.
What is viviparism and its characteristics
In the viviparous animals, the young develop inside the mother's body and their young are born alive directly from the mother, depending on his mother to survive to complete development. The origin of the word viviparous is in Latin viviparus, a term that refers to the gestation and birth characteristics of the young.
Viviparous mammalian animals present 2 features main:
Sexual reproduction
The offspring develop as embryos inside their mother's body, for this reason it is necessary for their parents to undergo internal fertilization, which requires copulation or sexual encounters with the opposite sex.
Viviparous animals are usually polygamous (with some exceptions), selecting their mates with care. The reason is to ensure the best possible genetic load for their offspring and, therefore, the highest probability of survival.
Gestation period
After fertilization, a period of time begins in which the female carries the embryo inside her and during which she develops the structures necessary to survive. This period of time called the gestation period varies in its duration depending on the species, the complexity of body systems, the size of their bodies or the development necessary to be born. Thus, we have the 21 or 22 months of the elephants until approximately 9 months of gestation, until the birth arrives. The number of offspring per species also varies greatly.
Viviparous Animal Types and Examples
According to the need of their young to be fed or not through the placenta, viviparous mammalian animals are divided into:
Placental viviparous
Those animals in which the offspring need a placenta that connects them to their mother and provides them with the oxygen and nutrients necessary for their development. The placenta is a highly evolved structure, so this type of viviparism is only found in highly evolved species, like the human being.
The placental viviparous have their origin approximately 160 million years ago during the Upper Jurassic and comprise approximately 5,100 known species. Regarding their characteristics, they are species of large size, slow reproduction, long life expectancy and a large brain. In their diet they can be carnivores, herbivores or omnivores.
Viviparous marsupials
The viviparous marsupial animals they are not as evolved as the placentals. Because these animals lack a placenta, their young are born underdeveloped and must pass through the fur of their mother's abdominal area until they reach the pouch, which is a bag-shaped structure located in the mother's abdomen, which provides them with protection, warmth and an abundant amount of milk, which allows them to continue their development.
At present, about 270 species of marsupials are known in the world, of which 70 inhabit America and 200 in Australia. They are believed to have developed during the Lower Cretaceous period from early pantotheriums. Among the marsupials we find koalas, kangaroos, opossums or Tasmanian devils.
You can learn more about them in this other Green Ecologist article on What are marsupial animals and examples.
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