What is a mammal?
You are a mammal! So are dogs, whales, bats, mice and elephants. There are about 6500 species of mammals.
All mammals share these traits:
| Trait | Description |
|---|---|
| Hair or fur | At some stage of life, even whales have a few hairs |
| Mammary glands | Mothers feed their young milk |
| Warm-blooded | Keep a steady body temperature |
| Backbone | They are vertebrates |
| Lungs | All breathe air, even those living in water |
| Three middle-ear bones | Help them hear well |
| Large brains | Compared with body size |
The word "mammal" comes from the Latin mamma, meaning breast.
Three groups of mammals
| Group | How young develop | Examples |
|---|---|---|
| Placental mammal | Inside the mother, fed through a placenta | Humans, dogs, whales, bats, horses (about 95% of mammals) |
| Marsupial | Born tiny; finish growing in a pouch | Kangaroos, koalas, opossums |
| Monotreme | Lay eggs | Platypus, echidnas |
A newborn kangaroo is about the size of a jellybean! It crawls into its mother’s pouch and stays for months. The Virginia opossum is North America’s only marsupial and is now found in southern Canada.
The platypus is especially strange: it lays eggs, has a duck-like bill that senses electricity, and males have a venomous spur.
Mammals everywhere
| Habitat | Mammals | Adaptations |
|---|---|---|
| Arctic | Polar bear, arctic fox, muskox | Thick fur, fat, small ears |
| Ocean | Whales, dolphins, seals | Blubber, flippers, holding breath |
| Air | Bats | Wings of skin stretched over long fingers; echolocation |
| Desert | Camels, kangaroo rats | Saving water, being active at night |
| Underground | Moles, gophers | Strong digging claws, tiny eyes |
| Forest | Deer, bears, squirrels | Varied diets, climbing, camouflage |
Bats are the only mammals capable of true flight. The blue whale is the largest animal that has ever lived, up to about 30 m long.
What mammals eat
| Diet | Teeth | Examples |
|---|---|---|
| Herbivore (plants) | Flat molars for grinding | Deer, rabbits, cows, beavers |
| Carnivore (meat) | Sharp canines for tearing | Wolves, lynx, cougars |
| Omnivore (both) | A mix | Bears, raccoons, humans |
| Insectivore (insects) | Small, pointed | Shrews, many bats |
Mammals are the only animals with different kinds of teeth (incisors, canines, premolars and molars). Teeth tell scientists a lot about a mammal’s diet.
Raising young
Mammals usually have fewer young than fish or insects, but they invest a lot of care in them. Mothers nurse their young with milk, which is rich in fat and nutrients and helps protect babies from disease. Many young mammals learn skills, like hunting, by watching their parents.
Canadian mammals
- The beaver is Canada’s national animal and appears on the five-cent coin. Beavers build dams that create wetlands for many other species.
- Moose, caribou (on the 25-cent coin), black bears, lynx, wolves and orcas are other well-known Canadian mammals.
Mammals in danger
Habitat loss, hunting and climate change threaten many mammals. In Canada, woodland caribou populations have declined, and the North Atlantic right whale is endangered. Conservation efforts include protected areas, hunting rules and ship speed limits in whale zones.
Common mistakes
- Thinking whales and dolphins are fish. They breathe air, nurse their young and are warm-blooded.
- Thinking bats are birds.
- Thinking all mammals give birth to live young. Monotremes lay eggs.
Try it yourself
- Make a chart of 10 mammals with their habitat, diet and group (placental, marsupial or monotreme).
- Look at pictures of skulls from a herbivore and a carnivore. Compare their teeth.
- Test insulation: put one hand in a bag of shortening ("blubber glove") and both hands in ice water. Which hand stays warmer?
Quick recap
- Mammals have hair, make milk, are warm-blooded and breathe with lungs.
- Placental mammals, marsupials and monotremes develop young in different ways.
- Mammals live on land, in water, underground and in the air.
- Teeth reveal a mammal’s diet.
- Many mammals need protection from habitat loss and climate change.