Are mammalian animals oviparous or viviparous?

As we have mentioned before, within mammals there are cases that can be considered the exception to the rule. In fact, the basic thing 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 they 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.

The oviparity is an ancestral characteristic and undeveloped within breeding methods, so mammals are mainly viviparous because animals are more highly evolved than the rest and have evolved in the form of reproduction. The only exception to this is the monotreme group , which includes platypus species and the echidna family. The monotremes represent a group of very primitive mammals that still maintain certain reptilian characteristics.

Among the characteristics of oviparous mammalian animals are:

• 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 inhabit only Tasmania, New Guinea and Australia .
• They are capable of living in captivity for up to 50 years.
• Male platypus can be poisonous.

In viviparous animals , the young develop inside the mother’s body and their young are born alive directly from the mother , depending on their mother to survive until they complete their development. The origin of the word viviparous is in the Latin viviparus, a term that refers to the characteristics of gestation and birth of the young.

Viviparous mammalian animals have 2 main characteristics :

Sexual reproduction

The offspring develop as embryos inside the body of their mother, for this reason it is necessary that their parents present an 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 best chance 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.

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 , such as humans.

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 animals marsupials are not as evolved as placental. 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 marsupium , which is a bag-shaped structure located in the mother’s abdomen. provides protection, warmth and an abundant quantity 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.