Mammals are one of the 6 main classes of animals and us human beings belong to this class. A mammal is a warm-blooded, air-breathing vertebrate (having a backbone or spinal column), and its warm blood facilitates it to live in any kind of climate, either hot or cold. Mammals are found all around the world. There are over 5500 species of mammals, ranging in size from the 30-40 millimeter bumblebee bat to the 33-meter blue whale.

Mammals are characterized by body hair or fur, three middle ear bones, a four-chambered heart, a single-boned lower jaw, and sweat glands. The female mammals possess mammary glands that secrete milk in mothers for nourishing the young. most mammals possess specialized teeth. A characteristic feature of mammals is their neocortex, a layer of the brain that gives them superior intelligence to reptiles and birds. The neocortex is involved in higher functions such as sensory perception, generation of motor commands, regulating body temperature, spatial reasoning, conscious thought, and in humans, language.

There are mainly three types of mammals:

Small mammals do not exist as a zoological group. The term is generally applied to mammals measuring less than one foot (including the head and body) and weighing less than 1kg. Most species of small mammals are rodents, small cats, insectivores (insect-eating), and bats. However, some dogs, bears, deer, small primates (such as lemurs), and carnivores (meat-eating, such as slender-tailed meerkats) are also included in the thing group. Small mammals are exclusive creatures; many are not nocturnal and very shy.

The only surviving examples of egg-laying mammals are the platypus and four species of echidnas (or spiny anteaters), all indigenous to Australia and New Guinea. The Platypus is a semi-aquatic creature, known for its duck-like bill (snout), beaver-like tail, and otter-like foot. The male platypus has a spur on the hindfoot that delivers venom, capable of causing severe pain to humans. Echidnas have coarse hair and spines, and their snout functions as both, a mouth and nose. They resemble the anteaters of South America and other spiny mammals like hedgehogs and porcupines but are not related to them.

Rodents are characterized by two continuously growing sharp incisors in the upper and lower jaws. They use these incisors to gnaw wood, break into food and bite predators. 40% of mammals species are rodents, and they are found in vast numbers on all continents other than Antarctica. Common rodents include mice, rats, squirrels, porcupines, beavers, chipmunks, guinea pigs, and voles. Most of them eat seeds, nuts, or plants, though some are omnivores (eating both, meat and plants).

Insectivores are small mammals that survive by eating insects, other arthropods, and earthworms. They make up almost 10% of all mammal species, comprising hedgehogs, moles, and shrews. The white-toothed pygmy shrew weighs less than 2.5 grams and is perhaps the smallest living mammal.

Nocturnal animals are active during the night and sleep during the day, the reasons for this are many; like cooler nights in the tropics or the cover of darkness from predators. They generally have highly developed senses of hearing and smell and specially adapted eyesight. Some of the nocturnal mammals are badger, red fox, opossum, raccoon, bat, skunk, bobcat, and weasel. Raccoons can grasp objects and can even open doors because of the shape of their paws.