Mammals: who they are and how they live

Mammals: who they are and how they live

Mammals are the most evolved class of the animal kingdom and to which man also belongs. They are vertebrates


in which we find 26 different orders with about 5000 species. It should be noted that scholars do not agree on the number of orders and species to be attributed to this class. The more and more recent phylogenetic studies cause great upheavals almost daily.


They are animals that we find in all continents, islands, oceans and seas in all habitats of the world. The varieties of life form present in the classMammalia (where we also find man), from shrews to bats that can weigh no more than 3 grams, to whales that weigh 160 t, to those that fly, jump, swim, run, adopting a whole series of precautions to occupy them more different ecological niches, makes us understand why these animals have a very important weight on biodiversity worldwide, having fundamental roles in different ecosystems.


They are warm-blooded animals and have three distinct characteristics that are not found in other animals: they breastfeed their young with the milk secreted by specific glands (mammary glands); they have three characteristic bones in the middle ear (stirrup, anvil and hammer) which are responsible for the transmission of sound; they have hair at some point in their development. They also have skin (skin) and hair (only some species that live in water have hair limited to a few regions of the body) and special skin glands such as sweat, sebaceous and, in some species, odoriferous. They have horny skin formations such as nails, horns and beak in the platypus.

A common feature is the presence of seven cervical vertebrae and a mandibular which articulates directly with the skull. Furthermore, most of the dentition consists of teeth located in special alveoli and different from each other (incisors, canines, premolars and molars) which are renewed only once in life (diiodontics).

They have separate sexes, sexual dimorphism in most species and generally a very developed brain.


Almost all species are polygamous; generally a male has more females considering that the female uses a lot of energy for gestation and lactation while the male in practice provides only the semen. This involves great competition of the males for the search of the female also because the females become demanding considering the quantity of energy they put in procreation.

Only 3% are monogamous within a breeding season and generally in this case the male helps in the rearing of the offspring.

All females are periodically subject to a hormonal change that leads them to produce one or more eggs ready to be fertilized by a male through the most various mating rituals. Once fertilization occurs, the female can raise the embryos in three different ways:

1) the eggs are laid outside the body and then hatched (Prototheria, which is the least evolved form that includes only one order: i Monotreme ) or in a nest (eg platypus) or in a special cutaneous bag (eg echidna);

2) partial growth of embryos inside the mother's body due to poor placental function with subsequent development in special omarsupi bags placed outside the mother's body (Metatheria). This characteristic is found in marsupials in general (kangaroos);

3) birth of the new individual from embryos developed thanks to a placenta that is directly connected to the uterine wall of the mother (Eutheria) with a more or less long gestation period (e.g. woman).

Once born they are nursed by their mother and cared for in the first period of their life enjoying what are called parental care, that is to say the parents (or a single parent) take care of the offspring until it is autonomous.


They can have very different life expectancies: in general, the small species have a shorter life than the larger ones, with some exceptions (for example, bats can live tens of years). from one year up to 70 years even if there are whale species (Balaena mysticetus) which can live up to 200 years.


How they behave and what lifestyles are it is almost impossible to describe them as general characteristics given the large number of species and the fact that they occupy practically all the ecological niches of the planet. In practice, whatever behavior and lifestyle comes to mind, surely there is some mammal that puts it into action, reasonably speaking.


Hearing, smell, sight and touch are used in communication and perception: smell is fundamental for nutrition, coupling and social communication, in fact many also use pheromones and other olfactory stimuli (urine, feces, glandular secretions) to communicate with one's fellowmen; hearing for echolocation, for example used in bats for navigation and for the search of food; the voice used in a very wide range of social behaviors such as territorial defense, reproduction, reporting in the group, etc; the sense of touch used for example through the hairs (whiskers or whiskers) or the skin; the sight, for example, is very important in nocturnal specimens or in any case for the search for food, navigation, etc.


Considering the great variety of species, eating habits can be more varied, finding carnivorous species (for example felines), herbivorous (for example cattle), omnivorous (for example primates).

Below are the monographic cards of the main mammals (Mammalia):

Single mammal monographs


Blue whale
(Balaenoptera musculus)

Fin whale
(Balaenoptera physalus)

Video: How Many Species Are There?