Mammals - Types & Characteristics
Mammals, with their unique features, gives an idea of how spectacular Earth's biodiversity can be. Through the process of evolution, they acquired a whole range of characteristics and adaptations that allow them to live in very varied climates and landscapes.
Over 5,000 mammalian species inhabit our world, an impressive number that encompasses creatures as small as mice and shrews, and as colossal as whales and elephants. Notably, this wide range also includes us, the humans.
On this page, we aim to open a window to the world of mammals, exploring their diverse types, key characteristics, and the roles they have within their ecosystems. So without further ado, let's get started!
8 Characteristics of Mammals
- Mammary glands: This is a unique feature of female Mammals. They have mammary glands that are able to produce milk in order to feed their offspring. Other vertebrates do not have this gland.
- Homeothermic metabolism: Mammals have a homeothermic metabolism, which means that they use metabolic processes to maintain a constant body temperature. This makes endothermy possible – see point below.
- Endothermy: Endothermy refers to the ability to be able to regulate the body’s temperature internally, and mammals are able to do that, no matter the environmental conditions.
- Hair or fur: Most mammals have their body covered with hair or fur, which greatly helps in maintaining a constant body temperature even in cold environments. A notable exception is the Cetaceans – marine mammals like dolphins and whales, which have lost their hair over the course of evolution.
- Three middle ear bones: Mammals have three middle ear bones, called ossicles, which make hearing possible.
- Four-chambered heart: Mammals’ hearts have four chambers, enabling the separation of oxygenated blood and deoxygenated blood. This makes the overall blood flow and the body’s oxygenation much more efficient.
- Central nervous system: Mammals have a complex central nervous system – the brain and the spinal cord. Thanks to this nervous system, mammals are able to better sense their environment and display complex behaviors.
- Live birth: Mammals don’t lay eggs, they directly give birth to live young.
These amazing adaptations allow mammals to survive and thrive in a variety of environments across the world, from polar regions to deserts and oceans.
The 3 Types of Mammals
Mammals are an incredibly diverse group of animals, but they are divided into only 3 main groups. Each group shares specific characteristics, and branches out into many other subgroups. Let's explore the 3 groups of mammals:
Monotremes
Monotremes are a bit of a classification nightmare. Remember how we established above that mammals give birth to live offspring and don’t lay eggs? Well, monotremes are an exception.
Monotremes are egg-laying mammals, and they are the most primitive type of mammals. They include species like the platypus and the echidna, and they can be found in Australia and New Guinea.
Marsupials
Marsupials also mostly live in Australia, plus a few species living in New Guinea. Their most distinctive feature is the presence of a pouch on the mother’s belly.
Marsupials give birth to underdeveloped offspring, that finish their development in this pouch until they are fully ready to survive on their own in the outside world. Kangaroos, wallabies, and koalas are marsupials.
Placental Mammals
This is the largest and the most diverse group of mammals. Their unique characteristic is the presence of a placenta, allowing the transfer of nutrients between the mother and the fetus developing in her belly.
Placental mammals include various groups of animals. Here are a few examples:
- Rodents: they are known for their sharp incisors, such as beavers, rats, and squirrels.
- Bats: they are the only type of mammals able to sustain flight.
- Cetaceans: these are marine mammals (whales, dolphins, porpoises…). One of their adaptations for marine life is the loss of their fur.
- Carnivores: a group of animals with sharp teeth and other adaptations enabling them to hunt their prey and eat meat. Some of the best-known carnivores include lions, tigers, and wolves.
Frequently Asked Questions About Mammals
All mammals have hair at some point in their life cycle, though the amount varies. For instance, humans have hair all over their bodies, while cetaceans like dolphins and whales are born with a small amount of hair which they lose as they age. It is an adaptation to their life in the ocean.
Most mammals give birth to live young, but there are exceptions. Monotremes, such as the platypus and echidna, are unique mammals that lay eggs.
No, not all mammals have periods. Menstruation is actually a pretty rare phenomenon in the animal kingdom, including among mammals. Apart from other primates, only a few species have periods, and they are less heavy than the periods humans experience.
Bats are the only group of mammals capable of sustained flight, as they are the only ones with functional, flapping, articulated wings. Other mammals, like flying squirrels and flying lemurs, can glide or parachute but not truly fly.
Whales and dolphins are classified as mammals because they share key mammalian traits: they are warm-blooded, breathe air through lungs, bear live young which they feed with milk produced by mammary glands, and have a certain amount of hair after birth (which they then lose as they age).
The belly button (or navel) is where the mother’s placenta is attached to the fetus, via the umbilical cord. Hence, placental mammals have belly buttons.
After birth, the newborn is able to breathe and eat on his own, this link to the placenta is no longer needed. Human belly buttons are among the biggest and most obvious, but they are also well visible on other larger mammals. On small mammals, the small scar often disappears under the fur.
Yes, all mammals are warm-blooded, a trait also known as endothermy. This means they can regulate and maintain their body temperature independently of the surrounding environment.
Learn More About Mammal Species
Links to articles packed with surprising facts and knowledge to further learn about amazing species of mammals, so you know what you are looking at on your next wildlife trip!
Our Mammal Fact Sheets (C):
