The mammals are the best known group of vertebrates, which give birth to live young and feed them with the milk produced by their mammary glands. They are easily adaptable to any environment and they adjust their behavior to ever-changing circumstances. They dwell on land, water and in the air.
Mammals have a single jawbone, in which the mandible is directly articulated to the cranium.
Mammals are the only animals that are covered with a layer of hair. Hair appears under different forms: whiskers, spikes, spines, horns (rhinoceros). The most common form is fur, which usually consists of an insulating undercoat and a protective coat that stands out, protecting the animal’s skin and giving coat color.
In some species, hair in the form of whiskers also has a sensory function. The most important is the animal’s skin. Their long existence is due mostly to the ability of maintaining a constant internal body temperature, regardless of changing external conditions.
The skin is composed of two layers: an external protective layer made of dead cells, called epidermis, and an interior layer, called dermis, containing blood vessels, nerve endings and glands.
Sebaceous glands secrete chemical substances which help mammals communicate with each other, the mammary glands produce milk with which they feed their newborn, and the sudoriferous glands, together with the hair, play an important part in adjusting body temperature.
Mammals are able to maintain a constant body temperature, which enables them to remain active under high temperature conditions, as well as under low temperature conditions. There is a specific area of the brain, also known as the hypothalamus, responsible for monitoring body temperature and adjust it when necessary. The manner in which mammals adapt their behavior also contributes to regulating body temperature.
In warm climate areas, mammals avoid overheating by resting when temperatures peak during the day. Panting is another cooling mechanism of mammals. Panting helps lower body temperature as it favors the evaporation of water from internal surfaces, like the tongue.
During the cold season, some mammals preserve energy through hibernation. During hibernation, body temperature lowers, metabolism rates fall to an almost imperceptible level, and they no longer eat; they survive based solely on the accumulated fat deposits. During hibernation, mammals are numb and difficult to wake up.
Aestivation is a phenomenon similar to hibernation, which entails lack of activity during the summer. Like hibernation, aestivation helps save energy when food is insufficient.