Viviparous animals are those that are born inside the pregnant parent, unlike oviparous animals that are born from eggs incubated outside. Viviparous animals are gestated in the female’s placenta, through which they receive all the oxygen and nutrients they need to develop and be born. In most cases, viviparous females give birth to fully developed offspring, or at least in an advanced state of growth, ready to grow autonomously.
Types of viviparous reproduction
Depending on the type of development of future offspring, viviparous animals are classified into three types.
Placental viviparous
They are those that develop in specialized structures within the female’s belly such as, for example, the human placenta, which adapts to the fetus and widens so that it can achieve optimal development.
Other placental viviparous animals would be dogs, cats, cows, horses, chimpanzees and elephants, etc.
Placental viviparity is considered a more evolved gestation system than the oviparous (gestation through eggs), since the breeding remains protected from external threats within the womb, giving it greater opportunities to survive.
Marsupial Viviparous
In this case, the offspring do not culminate in their development inside the female’s womb, but in external structures that fulfill a placental-like function so that they finish forming. The classic example is kangaroos.
In addition to kangaroos, koalas, opossums and the Tasmanian devil are also marsupial viviparous.
Ovoviviparous
Here the gestation is carried out inside an egg, but this is kept inside the female’s body until the end of its growth phase. The egg can hatch inside or outside the maternal body. The boa constrictor reproduces through eggs that remain inside the mother until the time of hatching.
Anacondas, Suriname toad, manta rays, platypus and seahorse are some species of ovoviviparous animals. In the case of seahorses, it is the males that carry the eggs inside.
Characteristics of viviparous animals
- In viviparous animals, fertilization is performed internally after the male’s sperm fuses to the female’s egg, forming the zygote.
- The young develop in specialized structures located in the female’s womb until the moment of birth, when they go outside through childbirth.
- The gestation time and the number of offspring vary according to the species. In humans, for example, gestation lasts 9 months, and most commonly, a single embryo develops. Cases of multiple gestations do not occur frequently. In dogs, gestation lasts between 58 and 68 days and an average litter can have between four and six offspring.
