Mammals

Lina is playing with her two cats, Alice and Bubbles. Lina loves her cats; she thinks they’re really smart, and she likes their soft fur. But Lina, do you know that cats are grouped into the same larger category of animals as blue whales? It sounds strange, because cats live on land and whales live in water; cats have fur and legs, whales don’t have fur or legs. But they actually have a lot more in common than you might think!

Let’s take a closer look. Both cats and blue whales, have a backbone, which means they are vertebrates. Both types of animal breathe with lungs: even though blue whales live underwater! Every half an hour or so, they need to come up to the surface to breathe air. They both regulate their own body temperature: they are warm-blooded.

Cats and blue whales both have a highly developed brain. The skin of cats and blue whales is covered in hair: cats have a very visible coat of fur, but whales actually have body hair too! The hairs serve different functions in these two types of animal though. In cats, their basic function is to help maintain a constant body temperature. In whales, they are mostly used for sensing their surroundings.

But the defining characteristic that groups both of these types of animal together, is that for quite some time after they are born, they only feed on milk. The milk is rich in nutrients, which help the young grow. It’s produced in specialised parts of the female body: the mammary glands. But it’s not just cats and blue whales that share these characteristics. More than 5000 other species have them too, among them, we humans!

The group, or CLASS, of animals that they belong to is called MAMMALS. But there is one major difference among mammals, which divides them into three distinct groups: the way in which they give birth! The majority of mammals, like blue whales, cats, and humans, give birth to live young. These mammals grow and develop in the womb, where they receive all the nutrients and oxygen they need, via a special organ called the placenta. Once they are born, they are still quite small, but they do have developed organ systems.

These mammals are placental mammals. Mammals like kangaroos and koalas, also give birth to live young, however their organs continue developing after birth. When they are born, they climb into a pouch on the front of the female body, where they feed on the milk, and continue to grow and develop. These mammals are marsupials. The third group of mammals includes the platypus and the echidnas.

These don’t give birth to live young: instead, they lay eggs, that the young hatch from! These mammals are called monotremes. Mammals are vertebrates, breathe with lungs, are warm-blooded, have highly developed brains, have body hair, and mammary glands. We too belong to this group of animals. But our behaviour, such as the destruction of the natural environment and pollution, puts mammals at risk of extinction.

We need to come up with solutions to maintain the incredible diversity of our class. Got any ideas Lina?