All mammals give birth to young ones, except platypus and echidna as they are egg-laying mammals.
So, the correct answer is 'Mammals'.
Monotreme mammals lay eggs instead of giving birth to live young. They are the only living order in the mammalian subclass called Prototheria, which also includes several extinct orders. Living monotremes include one species of platypus and four species of echidna (see Figure below, Figure below, and Figure below).
It is not only humans and 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 her body, as in mammals.
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.
Elephants are placental mammals, which means their young grow inside of the mother and are fed through a placenta that is attached to her body. Elephant babies are born live, not hatched from eggs.
Dolphins give birth to live young and do not lay eggs. They can get pregnant on average every two to four years once they're mature, although some species can have 5-7 years between births.
Most animals that procreate through parthenogenesis are small invertebrates such as bees, wasps, ants, and aphids, which can alternate between sexual and asexual reproduction. Parthenogenesis has been observed in more than 80 vertebrate species, about half of which are fish or lizards.
There are over 500 species of shark living in waters around the world and the majority give birth to live young. The remainder are oviparous, meaning they lay eggs.
Many sharks are viviparous, meaning they give birth to live young. Like all sharks, species such as blue, bull, and hammerhead sharks rely at first on a yolk sac for nutrition. But they also develop a placental connection similar to a mammal's umbilical cord.
Aphids, tiny insects found the world over, are “essentially born pregnant,” says Ed Spevak, curator of invertebrates at the St. Louis Zoo.
While most snakes are oviparous, laying large clutches of leathery eggs, some species are known to be viviparous, undergoing live births instead. Snake species that lay eggs include garter snakes, water snakes, most vipers, boas, sea snakes and death adders.
While most mammals also require a break between pregnancies, either to support new young or during periods of seasonal lack of resources, the female swamp wallaby is the only one that can claim the reproductive feat of being permanently pregnant throughout its life.
All crocodiles lay hard-shelled eggs, which may weigh 50–160 grams (0.1–0.4 pound) each. A female lays an average of 12–48 eggs per nest, depending upon her age, size, and species.
The Australian three-toed skink (Saiphos equalis) is doubly remarkable: Not only can it both lay eggs and bear live young, but it can do both within a single litter of offspring.
Contrary to what some may believe, whales are not fish and do not lay eggs. Female whales carry their unborn fetus in the womb and when it is time to deliver, they will give birth to a live, oxygen breathing, baby whale.
You might have learned in school that reptiles are different from mammals because they lay eggs. While approximately 70% of snakes lay eggs, others don't. Snakes living in especially colder climates have live births because the eggs wouldn't survive outside.
Most frogs' lay their eggs in water, but there are exceptions. Frog eggs do not have a shell, so they need some kind of moisture to keep them from drying out until they hatch. Some frogs have come up with amazing ways to keep their eggs wet besides laying them directly in water.
How are mermaids born? Once again, assuming mermaids reproduce the way fish do, mermaid babies would be born by hatching from eggs. Though it is possible for mermaids to get pregnant and give live birth like dolphins.
Many species of fish, like the kobudai, are known as “sequential hermaphrodites”: they can switch sex permanently at a specific point in their lives. The majority of “sequential hermaphrodites” are known as “protogynous” (Greek for “female first”): they switch from female to male.
The gastric-brooding frog is the only known frog to give birth through its mouth. According to researchers at the University of South Wales, the frog lays eggs but then swallows them.
How do whales give birth? Because whales are mammals, their calves grow inside their mothers and are born through live births. During the whale birth process, calves will emerge fins first.
In conclusion, whales and dolphins do not lay eggs because they are marine mammals. Therefore, they give birth just like us humans. However, gestation depends on the species.
There are some common methods and positions for sleeping. These include simply resting quietly in the water, either horizontally or vertically, or sleeping while slowly swimming next to another member of their pod or in small groups.