What makes a mammal?
The features all mammals share, the three groups (egg-laying, pouched and placental mammals), different kinds of teeth, and how blubber keeps sea mammals warm. Then run a fair test on blubber.
Read
There are about 5,200 kinds of mammal. All of them have hair and mammary glands, which make milk to feed their young.[1]
Mammals are endotherms: they keep a fairly constant body temperature. Hair traps a layer of air close to the body to keep heat in, and special hairs called whiskers help them feel their way.[1][7]
Most mammals have different kinds of teeth: incisors, canines, premolars and molars. Most also grow two sets of teeth in their lifetime, just as you have milk teeth first.[1]
Mammals form three groups. Monotremes (the platypus and echidnas) lay eggs. Most marsupials, such as kangaroos and koalas, carry their very tiny young in a pouch. Placental mammals, including humans, feed the baby inside the mother through a placenta; they are the biggest group.[1]
Whales, dolphins and seals live in cold seas. A thick layer of fat called blubber keeps them warm and stores energy for when food is short.[6][3]
Bats are the only mammals that flap their wings to fly. Many find insects in the dark by echolocation: they make high sounds and listen for the echoes.[5]
Try it: Blubber test
You need
- Four zip-lock sandwich bags
- Vegetable shortening or lard (about 250 g)
- Two thermometers or temperature probes
- A large bowl of ice and cold water
- Sticky tape, spoon, paper towels
- Timer
Safety
Do not keep hands in ice water for more than a few seconds. Wipe up spills and fat straight away so the floor is not slippery. Check for food allergies before handling fats. Wash hands afterwards.
What to do
- Make a 'blubber bag': put a layer of shortening about 2–3 cm thick in a zip bag, push a second bag inside it and tape the tops together so the fat is trapped between the bags.
- Make a 'no blubber' bag the same way, but with nothing between the two bags.
- Put a thermometer inside the inner bag of each one. Record the starting temperatures.
- Push both bags into the ice water at the same time, to the same depth.
- Record the temperature inside each bag every minute for 10 minutes.
- Fair test: what did you keep the same? Repeat if you have time, and draw a line graph of both bags.
What happens, and why?
Blubber is a thick layer of fat that insulates sea mammals from the cold water. Heat moves out of the bag with no blubber much faster, so its temperature drops quickly; the fat layer slows the heat loss, just as blubber keeps a seal or whale warm.[6]
Play: Which group of mammals?
Is it a monotreme, a marsupial or a placental mammal?
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Quiz
Other ages: Ages 6–7 · Ages 15–16