Common Features And Traits Of Mammals

What do Marsupials, Primates, Rodents, Whales, and humans have in common? They are all mammals. The mammals include the largest animals on the planet, the rorqual whales, as well as some of the most intelligent, such as elephants, some primates and some cetaceans. The basic body type is a four-legged land-borne animal, but some mammals are adapted for life at sea, in the air, in the trees, or on two legs. The largest group of mammals, the placentals, have a placenta which feeds the offspring during pregnancy. Mammals range in size from the 30–40 mm (1.2–1.6 in) bumblebee bat to the 33-meter (108 ft) blue whale.


The word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma ("teat, pap"). All female mammals nurse their young with milk, which is secreted from special glands, the mammary glands. According to Mammal Species of the World, 5,416 species were known in 2006. These were grouped in 1,229 genera, 153 families and 29 orders. In 2008 the IUCN completed a five-year, 1,700-scientist Global Mammal Assessment for its IUCN Red List, which counted 5,488 accepted species at the end of that period. In some classifications, the mammals are divided into two subclasses (not counting fossils): the Prototheria (order of Monotremata) and the Theria, the latter composed of the infraclasses Metatheria and Eutheria. The marsupials comprise the crown group of the Metatheria and therefore include all living metatherians as well as many extinct ones; the placentals likewise constitute the crown group of the Eutheria.

Except for the five species of monotremes (egg-laying mammals), all modern mammals give birth to live young. Most mammals, including the six most species-rich orders, belong to the placental group. The three largest orders, in descending order, are Rodentia (mice, rats, porcupines, beavers, capybaras, and other gnawing mammals), Chiroptera (bats), and Soricomorpha (shrews, moles and solenodons). The next three largest orders, depending on the classification scheme used, are the primates, to which the human species belongs, the Cetartiodactyla (including the even-toed hoofed mammals and the whales), and the Carnivora (cats, dogs, weasels, bears, seals, and their relatives). While the classification of mammals at the family level has been relatively stable, different treatments at higher levels—subclass, infraclass, and order—appear in contemporaneous literature, especially for the marsupials. Much recent change has reflected the results of cladistic analysis and molecular genetics. Results from molecular genetics, for example, have led to the adoption of new groups such as the Afrotheria and the abandonment of traditional groups such as the Insectivora.

Mammals are Diverse

Mammals are vertebrates that have many varied adaptations, allowing them to survive in a diverse habitats. The majority of mammals are warm-blooded. They breath air. They give birth to live babies, they nurse their young with milk produced from their mammary glands.

 Common Traits Shared By All Mammals

Let's take a closer look at a few of the traits common among mammals.

Warm-blooded: All mammals are endothermic or warm-blooded. This simply means, regardless of the temperature around them, mammals generally regulate a consistent body temperature.

Nursing: Mammals have mammary glands which they use to produce milk and nurse their young. The milk sustains their young with the nutrients that help them survive and grow.

Single Lower Jaw: Mammals have a lower jaw, or dentary, that is comprised of one bone. It attaches to the skull and supports the bottom teeth. Other vertebrates have multiple lower jaw bones.

Specialized Teeth & Tooth: Replacement Mammals have teeth that are adapted to their specific diets. Felines and canines have sharp incisors that allow them to tear meat, for example.

Mammals Have Similar Internal Structures

Four-Chambered Heart: Mammals have four-chambered hearts. A four-chambered heart separates deoxygenated and oxygenated blood. This helps mammals to regulate their body temperature. It also increases their metabolisms, helps to support their muscular activity, and increases their endurance.

3 Middle Ear Bones: Another characteristic of mammals is that they have a distinctive arrangement of 3, tiny bones in their middle ear. These bones transmit sound to the inner ear where it is converted into electrical impulses that are received by the brain and interpreted as sound.

Hair: Another distinctive characteristic of mammals is that they grow hair at some point in their lives at least somewhere on their bodies. The hair can take many different forms, ranging from quills, to eye brows, eye lashes, fur and even whiskers.