Mammals do not have vertebral column

The offspring suckle from their mothers

The temperature is over 50º

All mammals have three kinds of teeth

Aquatic mammals have lungs

The bat has two wings

    3. Monotremes

   They do not have teeth and the head extend into a horny beak. They are mammals that lay eggs and live in Australia and nearby islands. For example: the platypus (see the picture) and the echidna.

    4. Marsupials

   The offspring of marsupials are very weak at birth and they finish their growth in a marsupial pouch that mothers have in the womb. The breasts are in this pouch. For example: the kangaroo (see the picture) and the opossum.

    5. Cetaceans

   They are mammals that live in water and have fish shape with a horizontal caudal fin. They do not have hind limbs and the front limbs have turned into flippers. The skin is naked or has little hair, but under it, cetaceans have a thick layer of fat that protects them from cold. At the top of the head, they have nasal cavities which they put out the water in order to breathe. For example: some cetaceans like dolphins and sperm whales have teeth (see the picture); other cetaceans like the whale do not have teeth, but some layers called baleen that serve to retain the food.

    7. Xenarthrans

   These mammals do not have incisors in both jaws. Others do not have canines or any tooth. They eat insects or leaves.  

   For example: the anteater (see the picture), the pangolin and the armadillo.

    8. Proboscidea

   They have a long proboscis, which is a sucking organ, and an offensive and a defensive weapon. The two upper incisors extend into two tusks where ivory is extracted.

   For example: the Asian elephant and the African elephant.

    9. Even-toed ungulates

   These mammals have more developed two middle fingers of the limbs. They rely on the floor with a couple of fingers. There are two groups:
   - Pachydermata, with four toes on the limbs. For example: the pig, the wild boar and the hippopotamus.
   - Ruminants, with two fingers. The stomach has four cavities: the rumen, the reticulum, the omasum and the abomasum. When animals eat grass, it downs to the rumen which works like a storehouse. When they are in the barn, they pass the balls of grass, a kind of vomit, to the mouth where they chew them carefully. They swallow the grass and then it goes to the stomach where digestion occurs. Some ruminants have horns and others do not. For example: cow (see the picture) , ox , bison , sheep , goats , antelopes , gazelles , deer , roe deer , reindeer , giraffes and camels .

    11. Odd-toed ungulate

   These mammals have more developed the middle finger of each limb. They rely on the floor by an odd number of fingers. 

   For example: the tapir and the rhinoceros have three fingers. The horse (see the picture), the donkey and the zebra have one finger on each leg.

    12. Rodents

   They are generally small and eat grass. The toes of legs have hoofs. The lower jaw is articulated with the skull, so it only moves back -and-forth and vice versa. That is why we call them rodents.

   For example: the rabbit (see the picture), the hare, the squirrel, the mouse, the porcupine and the guinea pig.

    13. Insectivores

   They usually eat insects and worms. Their limbs are short and end in five toes.

  For example: the mole (see the picture) and the hedgehog.

    15. Chiroptera or bat

   They are mammals adapted for flight and their upper limbs have turned into wings. Bats always sleep upside down hanging with the hoofs of the rear legs. Thus, they can drop, extend their wings and flight. They eat insects at night.  

   For Example: common long-eared bat (see the picture) and the vampire.

    16. Carnivores

   They are mammals that eat meat. The incisors are small and sharp; the canines are long and sharpen for tearing the prey and the molars have cutting tips. Their claws are strong to hold and tear the prey.

   For Example : the dog (see the picture), the wolf , the fox , the jackal, the hyena , the tiger, the panther, the leopard, the lynx, the cat, the pine marten, the ferret, the weasel, the stoat, the otter, the brown bear and the polar bear.

    17. Pinnipeds

   They are carnivores mammals adapted to aquatic life. Their body has the shape of fish and their limbs are transformed into flippers. The fingers have hoofs and the body is covered with a short coat, but thick. They live in the cold waters of the North and South Pole of the Earth.

  For example: seals (see the picture) and walruses.

    18. Primate or apes

   They are mammals that climb trees. Some of them eat fruits and others eat any other substance (omnivores).

  For example: the monkey (see the picture), the capuchins, the mandrill, the macaque, the orangutan, the gorilla, the chimpanzee, the aye -aye and the sunda flying lemur.