What are mammals?
- Mammary glands make milk for the young. This is the key feature.
- Hair or fur on the body (even whales have a few hairs).
- Warm-blooded: body temperature stays steady.
- Four-chambered heart and lungs.
- External ear flaps (in most) and different kinds of teeth (incisors, canines, premolars and molars).
- Most give birth to live young.
Monotremes, marsupials, placentals
- Monotremes (platypus, echidna): lay eggs. They have milk glands but no nipples; the young lick milk from the mother's fur.
- Marsupials (kangaroo, koala, opossum): give birth to very tiny young that crawl into the mother's pouch (marsupium) and feed on milk for months.
- Placental mammals (dog, cow, elephant, human, whale): the baby grows in the womb, joined to the mother by the placenta, which brings food and oxygen and takes away waste. They are the largest group.
Main orders of mammals (six to know)
An order is a group of related families. Learn at least six:
- Rodents (rat, squirrel, porcupine): front teeth that never stop growing.
- Carnivores (tiger, lion, dog, cat): sharp canine teeth for meat.
- Primates (monkey, ape, human): big brain, hands that grip.
- Hoofed mammals (cow, horse, deer): plant-eaters that walk on hooves.
- Bats (chiroptera): wings made of skin; the only flying mammals.
- Whales and dolphins (cetaceans): live in water, breathe with lungs through a blowhole.
Rodents as disease carriers
Rats and mice live near people and eat our stored food. They can carry germs and fleas. Diseases linked to rodents include plague (by rat fleas), leptospirosis (from urine in water) and hantavirus. They also spoil grain.
Control: keep food covered, keep houses and drains clean, use traps, and keep cats. Do not touch dead rats with bare hands.
Try it
Use the 3D: choose each group and slide the time. Make a small table: where does the baby grow, and what does it drink? At home, look at pets and cattle and list the mammal features you can see (hair, ears, teeth).
Key formulas and definitions
- Mammal = mammary glands + hair + warm blood + 4-chambered heart
- Monotremes: lay eggs. Marsupials: pouch. Placentals: womb and placenta.
- Six orders: rodents, carnivores, primates, hoofed mammals, bats, whales and dolphins
- Rodent incisors grow all the time and are worn down by gnawing
Worked examples
1. Why is a whale a mammal and not a fish?
A whale breathes with lungs, is warm-blooded, gives birth to live young and feeds them milk. These are mammal features.
2. How does a baby kangaroo differ in birth from a baby dog?
A kangaroo is born tiny and finishes growing in the pouch. A puppy grows longer inside the womb and is born well developed.
3. Name two ways to reduce disease spread by rats at home.
Keep food and waste covered and the house clean so rats find no food, and use traps or keep a cat.
Common mistakes
- Saying all mammals give birth to live young. Platypus and echidna lay eggs.
- Thinking a bat is a bird because it flies. A bat has fur and feeds milk to its young.
- Calling dolphins fish. They are mammals that breathe air.
- Thinking a marsupial baby is born big. It is born the size of a bean.