Large mammals, such as primates, cattle, horses, some antelopes, giraffes, hippopotamuses, rhinoceroses, elephants, seals, whales, dolphins, and porpoises, generally are pregnant with one offspring at a time, although they may have twin or multiple births on occasion.
Animals that give birth to babies are called mammals. So, the animals, reproducing the babies of their own kind, by directly giving birth, are called mammals. For example, human beings are mammals. Cats, dogs, cows, horses, elephants, goats, pigs, lions, rats, squirrel etc.
Animals like humans, cows, dogs, cats, lions etc. give birth to young ones. At the same time, there are animals like insects, birds, fishes, and reptiles that lay eggs to reproduce.
Livebearers are aquarium fish that retain the eggs inside the body and give birth to live, free-swimming young. Among aquarium fish, livebearers are nearly all members of the family Poeciliidae and include: guppies, mollies, platies and swordtails.
Egg-laying Mammals
There are only five living monotreme species: the duck-billed platypus and four species of echidna (also known as spiny anteaters). All of them are found only in Australia and New Guinea.
On other hand, Kangaroo are pouched mammals. They don't lay eggs, their young one is born in an immature state. Gestation period shows complete development in the abdominal pouch or marsupium. So option (A) can't be the answer.
Mammal babies are born alive and look a lot like their parents. Mothers or sometimes both parents take care of the babies until they are able to take care of themselves. Female mammals produce milk to feed their babies. Milk helps babies grow and develop.
Only two mammals lay eggs: the platypus and the echidna. All other mammals give birth to live babies. Of all the birds that lay eggs, hummingbirds lay the smallest eggs, and ostriches lay the biggest eggs.
Most snakes are oviparous, meaning they lay eggs. However, there are a few species of viviparous snakes, which give birth to live young. The females of some viviparous species actually retain the eggs inside their bodies until they hatch.
As for us mammals, only two types lay eggs: the duck-billed platypus and the echidna. After a three-week pregnancy, the short-beaked echidna of Australia makes a nursery burrow, where she lays her egg directly into her pouch, incubating it for ten days until it hatches into a baby.
Placentals and marsupials are viviparous, meaning they give birth to live offspring. Marsupials, such as kangaroos, koalas, and our local Virginia opossum, give birth to very immature, embryo-like offspring that complete their development outside the womb usually attached to a nipple in a pouch.
It is not only mammals that give birth. Some reptiles, amphibians, fish and invertebrates carry their developing young inside them. Some of these are ovoviviparous, with the eggs being hatched inside the mother's body, and others are viviparous, with the embryo developing inside their body, as in the case of mammals.
Some animals reproduce by laying eggs. These animals are called oviparous animals. Examples of oviparous animals include fishes, frogs, snakes, lizards, insects and birds. The majority of the animals reproduce by laying eggs.
The vast majority of animals need to breed to reproduce. But a small subset of animals can have offspring without mating. The process, called parthenogenesis, allows creatures from honey bees to rattlesnakes to have so-called “virgin births.”
Seahorses and their close relatives, sea dragons, are the only species in which the male gets pregnant and gives birth. Male seahorses and sea dragons get pregnant and bear young—a unique adaptation in the animal kingdom. Seahorses are members of the pipefish family.
Crocodilians are either hole nesters or mound nesters. That is, they either excavate a hole, usually in sand, and bury their eggs, or they construct a mound, usually out of vegetation, and deposit their eggs in the centre of it.
A female platypus usually lays only two eggs at a time and rarely leaves her stream-side den while nursing her young. When she does leave, she plugs the den opening with dirt. The platypus is one of just a handful of mammals that lay eggs.
Egg production
Hens begin laying at around six months of age and can continue for five to 10 years with peak production occurring in the first two years. They will lay roughly six eggs each week. Egg production drops each year when the hens molt (replace their feathers in the early fall) and as daylight hours are lost.
The swamp wallaby is the only mammal that is permanently pregnant throughout its life according to new research about the reproductive habits of marsupials. Unlike humans, kangaroos and wallabies have two uteri. The new embryo formed at the end of pregnancy develops in the second, 'unused' uterus.
For some, of course, it's normal to only have one or a couple offspring in a lifetime. But swamp wallabies, small hopping marsupials found throughout eastern Australia, are far outside the norm: New research suggests that most adult females are always pregnant.
Seahorse fathers break all the rules—they're the onces who get pregnant and give birth. After the seahorse mother deposits her eggs into the father's pouch, the father fertilizes the eggs and incubates them until he gives birth to the tiny, fully-formed seahorses. This happens after about 20 to 28 days of pregnancy.
Females begin mating, and can breed, when they are two years of age, generally giving birth once a year, for the next 10 to 15 years. The gestation period of a female koala is 35 days, after which she gives birth to a single joey. Female koalas are also capable of giving birth to twins, however this is quite rare.
Monotremes are a unique group of mammals that lay eggs instead of giving birth to live young. Found only in Australia and New Guinea, monotremes are a fascinating example of the diversity of life on our planet. There are only three species of monotremes: the platypus and two species of echidnas.
The reason may be primarily about profitability. Turkey's take up more space, and don't lay eggs as often. They also have to be raised for quite a bit longer before they begin to lay. This means that housing and feed-related expenses would be considerably higher for turkey eggs compared to eggs from chickens.