Mammals are perhaps the most diverse community of animals that are present on the planet. Understanding the origin, evolution, existence and survival of mammals requires the use of archaeological records as evidence. Recent discoveries of fossil records reveal important details on the origin, evolution, existence and survival of mammals. Mammals are present in different geographical areas in a variety of sizes, shapes, and forms. These types of variations aid mammals in demonstrating adaptive behaviour to adjust to changing environmental and habitat conditions. The life and existence of mammals are possible only by the communication and interconnection that exist between one another. Mammals are large in number and hold a vital position in the entire operation of the world. In this article, you will learn more about mammals, the origin of mammals, examples of mammals, characteristics of mammals and some FAQs.

Origin of Mammals:

From the identified archaeological remains, it can be concluded that the mammals have been developed or evolved from early amniotes. Early amniotes can be categorized into two primary sets of species, they are synapsids and sauropsids. All mammals which also include extinct animals are thought to have sprung from synapsids. The extinction of synapsids during the Jurassic period has led to the evolution or development of the first mammal on earth. Sauropsids are highly different from synapsids. Sauropsids differ concerning their skull structure and the number of temporal fenestrae behind the eyes. It is estimated that the formation of mammalian life on earth would have occurred 200 million years ago. The Cenozoic era can be popularly called the age of mammals.

Characteristics of Mammals:

The physical characteristics of mammals are complex and different compared to other organisms on earth. Some of the adaptations and characteristics of mammals are listed below:

• Mammary Gland: These are possessed by all mammals and plays a key role in the secretions of mammary fluids while giving birth to offspring.
• Skin: A nonvascular epidermis layer on the outside and a corium layer on the inside make up the structure of the mammalian skin. Fats and organic salts are found coating the surface of mammalian skin. Antifungal and antibacterial characteristics are exhibited by the coat.
• Teeth: Teeth are highly organised and developed in mammals. They play a key role in allowing them to eat different varieties of foods from herbs, shrubs, and barks, to other animal flesh.
• Hair: They are both with and without hair and this highly depends on the habitat the mammal lives in. Aquatic mammals are found with fewer hairs and terrestrial mammals are found with well-developed hairs.
• Body shape: They are unique and vary for different sets of mammals based on their environment. Mammals are larger in size compared to other animals. Their structure is highly different and composite.

Other characteristics of mammals are, they are warm-blooded animals, possess sebaceous and sweat glands, exhibit a highly compounded brain, have sensitive skin, have a well-developed organ system and consist of organised bones and skeletal system. 

Classification of mammals:

Mammals are classified into various types based on their habitat, size, shape, morphology, physiology, reproduction, environment, etc. The most common classification followed is based on their reproduction. They are:

1. Eutheria: Placental mammals, also known as Eutheria, are a varied group of mammals with almost 4000 species identified. All placental mammals bear and deliver live offspring from their womb. In this case, the developing babies are nourished in the mother’s womb until birth by the placenta. The placenta is a specialised embryonic organ linked to the uterus wall. The common examples of mammals belonging to Eutheria are elephants, bats, mice, dogs, whales, sheep, horses, cats, monkeys and humans. 
2. Metatheria: The mammals belonging to Metatheria are also known as marsupials. They are roughly 272 species of metatherian mammals existing on earth. Marsupials differ from placental animals in several significant characteristics. The early gestation in these mammals results in the presence of underdeveloped babies in their pouches connected to their mammary glands. The babies move out after complete development. The common examples of mammals belonging to Metatheria are Kangaroos, opossums, Tasmanian devils, wombats and koalas.
3. Prototheria: Any of the mammals whose offspring develop inside the egg set down by oviparous females are called prototherian mammals. The majority of the mammals in this class are no longer in existence. The common examples of mammals belonging to Prototheria are platypus and echidna. 

Conclusion

Mammals being smart and well-developed organisms among all the species can be traced back to ancient amniotes. The fossil records obtained to date from various parts of the world demonstrate how mammals and early amniotes are connected. Domestication began as a food resource and animal entertainment, but it has now gained economic significance. Because of their excellent migratory tendency, mammals have a wide range of species on the planet. Physical structures and their ability to withstand their habitat assist them in communication, survival, transportation and reproduction. Being complex organisms, mammals have ruled the world in recent times. The absence of any organisms can completely break the life chain.