We explain what mammals are and what their main characteristics are. Also, the types of mammals and some examples.
What are mammals?
Mammals are known as vertebrate and warm-blooded animals belonging to the class mammalia, whose essential characteristic is that females have mammary glands that serve to generate milk with which to feed their young. Some 5,486 current species of mammals are known, including humans, and most of them are all viviparous, except the monotremes (such as the platypus).
The mammals date back approximately 200 million years, from some common ancestor derived from the synapsid or mammalian reptiles, which emerged during the Triassic Period. But unlike reptiles, they have the ability to regulate body temperature, which may have been key to their survival of the K-Pg (Cretaceous-Paleogene) Mass Extinction Event that extinguished non-avian dinosaurs.
Mammal characteristics
Mammals are an extremely diverse and numerous group of animals, of the most and best studied by humans among the entire animal kingdom. The morphological diversity of its component animals is such that they serve as examples from a blue whale, a giraffe and a kangaroo, to a dog, a platypus or the human being himself.
However, all mammalian species share certain minimal characteristics, such as:
- Presence of mammary glands. Located in the body of the female of the species, with which they secrete milk and suckle their young.
- Mandible composed of a dental bone. Instead of various bones or moving parts. In addition, the mandible articulates with the skull between the dental and the squamosal.
- They have an ear with three ossicles. Known as anvil, hammer and stirrup, with the exception of monotremes (which have reptilian hearing).
- They present hair in almost all stages of their life. And all species have it to some extent.
- They can regulate body heat. Through sweating, tremors and other ways of preserving homeostasis without resorting to external elements.
Types of mammals
A first classification of mammals is given by distinguishing between the ways in which their young are formed, as follows:
- Monotremes. Those few species of mammals whose females lay eggs after being fertilized. It is the evolutionarily oldest group of the group.
- Marsupials. These species (around 300) of mammals give birth to their young after a short gestation period, after which they must climb through the mother’s skin until they enter a skin sac known as a marsupium, within which they will be protected and will have access to the breasts. After several months, when they are fully formed, they will leave the pouch to begin their independent life.
- Placental. Most species of mammals belong to this category, characterized by gestating their young for several months and then giving birth when they are ready to lead an independent life. In the case of humans, however, the offspring are born in a high state of defenselessness that requires almost complete care during their first years of life.
Marine and terrestrial mammals
Although mammals evolved as a terrestrial species, and the vast majority lead a continental life, they also there have been the case of certain terrestrial species that have returned to the aquatic habitat, adapting his body in the process to swimming. Thus, they have changed legs for fins, mutated the type of fur and altered the proportions of fat in their body to conserve heat, although they have not lost lung respiration, breastfeeding, or other characteristic physical features in the process.
On the other hand, there are no flying mammals, with the exception of the bat.
Examples of mammals
Examples of mammals abound in everyday life and in other natural settings:
- The human being himself. As well as primates and apes in their entirety.
- Dogs and canids all. From our common pets, through wolves, jackals and hyenas.
- The felines all. From cats to lions, panthers, tigers, etc.
- Milking animals. Like sheep, cows or goats.
- Aquatic Mammals. Like the dolphin, the blue whale, the sea lion, the seals or the manatees.
- The large African and American ruminants. Like rhinos, giraffes, buffalo, etc.
- The bats. Unique genus of flying mammals.