Characteristics of mammals for kids

Mammals are a group of animals that have their own characteristics that differentiate them from other animals. For example, cats and dogs are mammals, but fish and parrots are not. We humans are also mammalian animals. What does this mean? It means that humans, dogs and cats are more alike than, for example, cats and fish.

What are mammals: definition for children             

Mammals are a class of vertebrate animals , that is, they have a skeleton of bones. Mammals have a key feature that differentiates them from other vertebrate animals (fish, amphibians, reptiles, birds): the young suck milk from the mother , that is, they feed on the milk produced by the mother’s breasts. This characteristic gives the name to this group of animals.

The first fossils of vertebrates have an age of 200 million years, they appeared in the Mesozoic Era in the Triassic period. They lived with the dinosaurs, but after their great extinction 65 million years ago, at the end of the Mesozoic Era, it was when they were most important on the planet. In the following era, in the Cenozoic (means “new life”), more species of mammals appeared and began to colonize the different environments of the Earth. Scientific studies have shown that the first mammal to inhabit our planet was similar to a small mouse.

Mammals are distributed over almost the entire planet. We can find them in marine ecosystems such as whales or dolphins, in freshwater ecosystems such as otters or in terrestrial ecosystems such as lions, bats or rabbits. In addition, some of them have different limbs that respond to the conditions of the environment in which they live: aquatic mammals have fins, terrestrial mammals have legs and flying mammals have wings to fly or membranes to glide.

Next, we are going to list and explain in a simple and easy-to-understand way what are the physical traits or characteristics of mammals :

  • Presence of hair: all mammals have hair on at least one part of the body. Some animals may be hairless due to adaptation to the environment in which they live, such as aquatic mammals. Hair protects from temperature changes, acts as a receiver of signals, and can be a weapon of defense and attack. Porcupines can throw quills to defend themselves, hedgehogs also have quills to protect them, and rhinoceros’ horns (made of very hardened hair) can be deadly weapons.
  • They have sweat glands: they allow the expulsion of sweat. Sweat allows the elimination of substances that are harmful to the body and helps regulate body temperature.
  • They are endothermic: they were formerly known as “warm-blooded animals.” It means that regardless of the temperature in the environment, your body has its own constant body temperature. That body temperature depends on reactions that occur inside the body that release energy in the form of heat.
  • They are viviparous: it means that the embryo (early stage of the offspring) develops inside the mother’s body. This is possible due to the existence of the placenta, an organ that provides food, allows the elimination of waste and offers protection to the embryo.
  • Presence of mammary glands: they are usually present only in females and produce milk. Milk is the first food of newborns and is very nutritious.
  • Presence of lips and a hard secondary palate: it is a trait closely related to the above. The existence of the lips allows suckling the milk that mothers produce. The palate allows the young to breathe as they feed.
  • Difiodonta dentition: in common language it refers to milk teeth and permanent teeth. Not all mammals have the same type of teeth or the same hardness, but they can change them at least once in their life.
  • Internal structure of the ear: in the ear there is a chain of ossicles, known as hammer, anvil and stapes, which are present in all mammals.
  • They present a varied diet: they can be herbivores, if they feed on plants; carnivores, if they eat other animals; insectivores, if they feed on invertebrates; omnivores if they have a mixed diet; or plankton eaters, if they feed on the small organisms that float in the water.

Before naming examples of mammals we must know something important. In order to better understand the history, characteristics and kinship relationships between species, it is necessary to order them into different subgroups. Taxonomy is the science that is responsible for ordering species. There are different taxonomic levels: domain, kingdom, phylum or division, class, order, family, genus, and species.

Mammals are classified as follows:

  • Domain: Eukaryotes
  • Kingdom: Animals
  • Edge or division: Strings
  • Class: Mammals

Now we are going to briefly describe some orders of mammals with examples , to see how they differ between them and what species they group together.


They are the only mammals that lay eggs . They are distributed in Oceania and include four species of echidnas and the platypus. For more information, we recommend you read this other article on Are mammalian animals oviparous or viviparous?


They are viviparous, but do not have a placenta. However, they have something similar, which we could call a primitive placenta, the pouch. The pouch is a cavity found on the outside of the female’s body and is where the embryo develops until it becomes the young.

Marsupial animals are possums, oppossums, bandicoots, koalas, wombats and kangaroos.

Placental or Eutherian

They are the most representative and abundant mammals. They are viviparous and do have an internal placenta, hence the name placentals. Let’s see the different orders:

  • Insectivores: shrews, hedgehogs, moles and tenrecs (only in Madagascar).
  • Toothless: elephant shrews, sloths, armadillos, and anteaters.
  • Dermoptera: flying squirrels.
  • Chiropterans: bats.
  • Scandentios: tupayas or shrews that live in trees.
  • Hiracoides: hirax.
  • Folidotos: pangolines.
  • Lagomorphs: rabbits, hares and pikas.
  • Tubulidentate: anteaters.
  • Sirénids : they are aquatic. Dugongs and manatees.
  • Proboscids: elephants, African and Asian.
  • Rodents: squirrels, marmots, rats, mice, beavers, porcupines, capybaras, hamsters, gerbils, voles, and lemmings.
  • Carnivores: most are predators. Bears, felines (cats, lions, tigers, cougars, etc.), canids (dogs, wolves, etc.), martens, otters, badgers, raccoons, sea lions and bears, seals, walruses and more.
  • Perissodactyls: they have hooves with odd toes (1 or 3). Horses, donkeys, zebras, tapirs and rhinos.
  • Atiodactyls: they have hooves with even toes. Pigs, cows, peccaries, hippos, camels, deer, sheep, goats, giraffes, and antelope.
  • Cetaceans: they are aquatic. Dolphins, sperm whales, porpoises, fin whales and whales.
  • Primates: can be subdivided into Strepsirrhines and Haplorhines. Strepsirrhines have a well-divided nose like lemurs, lorises, and galagos. Haplorhines have a flat, undivided nose like tarsiers and apes (gibbons, orangutans, gorillas, chimpanzees, and bonobos). Human beings and our ancestors are Haplorhine Primates and within this, we are apes.

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