An Exploration Of Viviparous Reproduction And Animals That Are Born This Way
Viviparous animals are those that give birth to live young rather than laying eggs. This reproductive style is widespread across many animal species, with the majority of mammals exhibiting viviparity as well as some fish, reptiles and amphibians.
Being viviparous means that the young develop inside their mother’s body and are nourished via the placenta, although there are some species that only partially rely on a placenta for nutrition. This allows the young to develop much more fully before they are born and reduces the time between conception and birth.
In this post, we look at what it means to be viviparous and how it compares to other methods of reproduction. We also look at some examples of viviparous animals across the animal kingdom.
Viviparity vs. Ovoviviparity vs. Oviparity
Viviparity is the most advanced method of reproduction as it allows the mother to monitor and adapt to her environment while providing her young with constant nourishment. Examples of viviparous animals include all placental mammals such as humans, cats, and dogs. Additionally, some reptiles, fish and amphibians are also viviparous.
Ovoviviparity is a form of reproduction where the embryo develops within an egg inside the mother’s body, but the egg does not receive nourishment from a placenta. Instead, it relies on yolk stored in the egg for nutrition. The egg is then hatched within the mother, and the offspring are born alive and fully developed. Examples of ovoviviparous animals include some sharks and reptiles, like rattlesnakes and slow worms.
In contrast to viviparity and ovoviviparity, oviparous animals lay eggs that develop outside of their mother’s body. These eggs are fertilized inside the mother and can contain a hard, protective shell or be soft and leathery. Examples of oviparous animals include the vast majority of amphibians, many fish, and most reptiles and birds, such as crocodiles or chickens.
In summary, there are three main methods of reproduction among animals – oviparity (egg-laying), ovoviviparity (egg-hatching inside the mother), and viviparity (live birth with nourishment from a placenta). Viviparous animals are the most advanced, allowing their young to receive the greatest amount of nourishment while still in the womb.
Examples Of Viviparous Animals
Viviparous animals are found in a variety of species from mammals to reptiles and amphibians. The most well known viviparous mammals include humans, cats, dogs, horses, cows, and bats.
Examples Of Viviparous Mammals
All placental mammals fall within the viviparous category, which includes nearly all mammal species except monotremes, and the two egg laying mammals which are duck-billed platypus and the echidna. Here are a few examples of the many viviparous mammals.
Bottlenose Dolphin (Tursiops truncatus)
All species of Dolphin are viviparous. These marine mammals all give birth to live young baby dolphins, which is something they share with other mammals of the sea like manatees and whales. All baby manatees and baby whales are live births and nourished internally by their mothers.
The most common of the dolphins is the Bottlenose Dolphin which inhabits warm and temperate seas worldwide, and may be found in all but the Arctic and the Antarctic Oceans.
The gestation period of the female Bottlenose Dolphin is 12 months. Calves are born in midsummer in European waters and between February and May in Florida. The young are born in shallow water, sometimes assisted by a ‘midwife’ (which may be male). The new single calf measures about 1 metre (3 feet) long at birth.
Elephants
Elephants are warm-bloodied mammals and members of the ‘Pachyderm’ species which means ‘thick-skinned animals’. They are the largest animal that lives on land, and there are two distinct species, the African Elephant and the Asian Elephant. In both cases, babies are born live after a gestation period within their mothers, where the foetus is provided nourishment from the placenta.
Most elephants live in the grasslands of Africa and in the forests of Asia although elephants can live in nearly any habitat that has adequate quantities of food and water. Young elephant calves are led by the older elephants with their tails and stay close to their mothers at all times.
Under the Endangered Species Act, the African elephant is listed as a threatened species and the Asian elephant is listed as an endangered species.
Chimpanzee
All primates are viviparous, which includes all monkeys, apes, gorillas, humans, and of course, the chimpanzee.
Some of the countries the chimpanzee is located in include Sierra Leone, Angola, Tanzania and Congo. They are intelligent animals and have a complex behaviour and communication system. There are several subspecies that live across their range, but they all have similar reproductive cycles.
The female Chimpanzee gestation period will last between 7.5 – 8 months and they will usually give birth to one infant. Twins do occur, but it is not common. Infants are weaned when they are about 3 years old, but usually maintain a close relationship with their mother for several more years.
Examples Of Viviparous Fish
There are several fish that are viviparous, but unfortunately, as of 2023 most fresh water viviparous fish species are now considered to be endangered by the IUCN Red List.
Viviparous fish allow their embryos to stay in the mothers body like ovoviviparous fish. However, the embryos of viviparous fish obtain needed substances from the mothers body, not through material in the egg. The young of viviparous species of fish are also ‘born alive’.
Here are some examples of viviparous fish.
Bull Sharks
Not all sharks are viviparous, but Bull Sharks are one of the species that are. These sharks get their name from the short, blunt shape of their snouts and their aggressive behavior. They are the third most dangerous sharks towards humans, just behind the great white shark and the Tiger Shark.
The young are carried in a yolk-sac placenta. The gestation period usually lasts 10 to 11 months, after which the young are born live and free-swimming.
Bull sharks normally give birth in fresh water or in the brackish water of freshwater river mouths. They do not rear their young, but the young use nursery areas in estuaries for protection.
Other sharks that are viviparous include the Requiem Shark, Blue Shark, Lemon Shark and Hammerhead Shark. There are around 20 viviparous species in total. Interestingly enough, there are both oviparous and ovoviviparous sharks too!
Zenarchopteridae – (Viviparous Halfbeaks)
Zenarchopteridae, otherwise known as viviparous halfbeaks, are a family of fish from the order of Beloniformes, which include many needlefish and flying fish species too. Some species, such as the wrestling halfbeak are popular as aquarium fish.
Despite their name, not all Zenarchopteridae are viviparous, but one particular genus within this family, the Dermogenys genus, are all viviparous. There are 12 recognized species in the Dermogenys genus, and the type specimen is the Dermogenys pusillus.
Examples Of Viviparous Amphibians
There are some amphibian species that are viviparous, including some frogs and salamanders, but it is much rarer than with mammals or fish. Here are some examples.
Fire Salamander (Salamandra salamandra)
While most Fire Salamanders are admittedly ovoviviparous, two of the thirteen subspecies are actually viviparous. These are the Salamandra salamandra fastuosa (Yellow-Striped Fire Salamander), and the Salamandra salamandra. bernardezi.
With these two subspecies, rather than larve being deposited into water after developing internally in eggs, the larvae continue their development within the female until they are eventually born as fully formed metamorphs.
Fire Salamanders are found throughout South and Central Europe, mostly at lower altitudes, between 250 and 1000 meters.
Nimba Toad (Nimbaphrynoides occidentalis)
The endangered Nimba Toad of West Africa, is the only frog that can be considered truly viviparous. Fertilization is internal and toads are developed inside their mothers before being born fully formed. These tiny anomalies are listed as of critical concern on the IUCN Red List, and local efforts are in place to try and protect at least some populations of the species.
Examples Of Viviparous Reptiles
Some reptiles also display viviparous reproduction, giving birth to live young instead of laying eggs. It is much more rare with reptiles however, than it is with mammals. Here are some examples of viviparous reptiles.
Boa Constrictor Snakes
Recently, it has been confirmed that some species of snake are fully viviparous, nourishing their young through a placenta as well as a yolk sac, highly unusual among most reptiles.
Retention of eggs and live birth are commonly, but not exclusively, associated with cold environments, as the retention of the young within the female allows her to control their temperature more effectively than if the developing young were in external eggs. In other words, this reproductive method is usually reserved for anmals that live in colder environments.
One such example which may be the exception to this rule, are most Boa’s including the Boa Constrictor. This snake resides in the Rainforests of Belize, Northern Mexico and Argentina in South America. Most types of Boa are viviparous, which makes them a bit of an anomaly. No one is entirely sure why the constrictors are live bearers but they are.
Boa Constrictors are seasonal breeders. The female of the species can give birth to as many as 50 live young at any one time. The babies develop inside their mother for around 4 to 5 months before emerging fully formed.
Some types of viper, including pit vipers, are also viviparous.
The Common Lizard
The Common Lizard (Lacerta vivipara), also known as the viviparous lizard, is a Eurasian lizard. It lives farther north than any other reptile species. It ranges across central and northern Europe and through to northern Asia.
The name of the species is derived from its ability to give birth to live young, an adaptation to a cool climate – but some southern populations are oviparous (egg-laying). The young develop for approximately three months inside the female. The 3 – 10 young (or eggs) are usually produced in July.
The young are black in color and measure about 3 centimetres and when first born are surrounded by egg membrane, from which they break free after about a day.