Mammals are the most highly evolved animals on the planet.
As per evolution theory, they originated from the reptiles like birds. But they have some interesting facts.
1. Give birth to young ones
Mammals, unlike birds, reptiles, etc., do not lay eggs. They give birth to fully formed young ones.
The young ones are developed in the womb of the mother and are delivered when fully formed.
These mammals lay their eggs, and once the babies are out, they nourish them with milk.
2. Mammary glands
Mammals are named so due to the presence of mammary glands.
Female mammals produce milk through these glands to nourish their newly born offspring.
3. Ability to fly
Mammals and birds are said to be evolved from reptiles. But unlike birds, mammals cannot fly.
The only exception to this rule is the Bat or flying fox.
They have wings that enable them to fly.
4. Socialize well
Most animals, like fish, amphibians, mollusks, etc., do not socialize much. But mammals socialize very well.
This is for the reasons like safety, rearing of offspring, food collection, etc.
5. Present in all the climatic conditions
They are present on the land, in oceans and even in places with extreme climates.
You can find camels in the hot and dry deserts and polar bears in the arctic circle with extreme cold and ice conditions.
Many mammals are also found on the hill and mountain tops, forests, deep caves, grasslands, etc.
5. Mammals have well-developed organs.
Most organs like the heart, brain, and kidney, which are not highly evolved in other animals, are developed in mammals.
For example, animals like fish, reptiles, and amphibians have two or three-chambered hearts.
But mammals have four-chambered hearts. Two chambers are meant for the handling of pure blood, and two for pumping impure blood.
6. They are the largest of all the animals on the planet.
Of all the animals, mammals are the largest animals. An elephant is the largest one on land, while the blue whale is the largest in the ocean.
They weigh a few tonnes and measure up to a few meters.
7. They have the same set of organ systems.
All mammals have the same set of organs and organ systems.
In other animals, there is variation in organs and organ systems between species and genera. This is not so among mammals.
8. Obligate vegetarians
Most animals are either vegetarians or non-vegetarians. They are clearly defined in most cases.
Mammals are the only group that has obligate vegetarians. These include the cow, goat, rabbit, buffalo, monkeys, horse, deer, etc. These are pure vegetarians in class.
Some of them are pure non-vegetarians like lions, tigers, hyenas, etc.
Few mammals prefer both types of diet. They can eat meat or a vegetarian diet based on availability.
These include mammals like dogs, cats, rats, etc.
Further, they tend to be part of the food chain. They are available for other animals as a part of the diet.
For example, birds eat rats, goats, monkeys, deer, etc. Reptiles like snakes and crocodiles eat rats, squirrels, buffaloes, humans, etc.
9. Concentrate their urine.
Most animals cannot concentrate their urine. This is because of the lack of Henley’s loop and vasa recta. In animals, these are present, and the urine flows in opposite directions, creating a counter current.
10. Presence of hair and glands in the skin
Most animals have scales on their skin, like fishes, birds, reptiles, etc. Or else the surface could be slimy, like in the amphibians, mollusks, etc.
But in animals, the skin gives out prominent hair. Besides, the skin may also have glands beneath it.