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Classification of Animals: Vertebrates & Invertibrates

There are two basic groups of higher animals.

Invertebrates do not have backbones.


What makes vertebrates different?
Vertebrates are the most complex organisms on Earth.

Vertebrates consist of around Fifty thousand different kind of animals.

It might seem like a lot.

Compared to the invertebrates, which include millions of different kinds of animals, there are not that many of vertebrates.

One reason is that vertebrates are usually larger than invertebrates.
They need more space.
Here we are going to learn about the characteristics of vertebrates and compare the different classes among themselves.

Vertebrates are called vertebrates because they have a well defined vertebral system or backbone.

Vertebrates are smart.
The brains of vertebrates are highly advanced compared to the invertebrates.

More cool traits about vertebrates are that they have muscles and skeletons.
Vertebrates are classified into five different classes based on their distinguishing and unique features.

The five classes of vertebrates are:

Pisces (Fishes)



Aves (Birds)


Each class is a step higher than the previous one in terms of evolution.

Now we are going to learn about each class separately:-

Pisces (Fish)
The first fish didn’t have jaws.
These fish suck on the sides of other fish
One good example is a Lamprey.

Though not as advanced as fish with real bones, fish with cartilage are the coolest fish out there.

Cartilage is a tough, elastic bone like substance which is almost the same as bone but is more soft and flexible.
These fish include species of sharks, rays, and skates.
And then the fish with real bones came along.

Bony fish were able to out-compete most of the fish that had cartilage for skeletons.
Goldfish have complex skeletons and are built to move. Some move really fast and are very strong.
Something like a tuna can move extremely quickly through the water


Most of the amphibians are slimy.
Amphibians left the oceans and lakes and came on to land.
Frogs and toad are examples of amphibians. They have four legs.
Salamanders are like frogs, but their body shape is more like a lizard. They are longer and have shorter legs.

You will often find salamanders around ponds and other small bodies of fresh water.


These animals have scales and breathe through lungs.
Let’s start with alligators and crocodiles.

Of the reptiles on Earth, the alligators, crocodiles, and others of this type are the largest around.

Did you know that some of them get larger than 18 feet long (over 6 meters)?

Snakes are special because they have no legs.

Lizards have scales just like snakes. They also have legs.
They can dig, climb trees, and grab things.

Turtles and tortoises are the special species that have shells.
Some are found in forests, some are in the water, and some are in the deserts.
Turtles and tortoises are able to live anywhere that the temperatures are warm enough.
They are also able to live a very long time, sometimes over 100 years.
Turtles are usually the ones found near water.
Tortoises are found on land and dry areas.

While amphibians are dependent on water at some point in their lives, reptiles made it away from the water.

Ave’s ( Birds)

Birds rule the sky.
There are small hummingbirds that suck nectar from flowers.
There are midsized crows with high levels of intelligence.
Then there are massive eagles that are some of the most capable predators on Earth.

Scientists believe special reptiles began to develop bird-like characteristics towards the end of the dinosaur era.

Do you know?

A species called Archaeopteryx had traits such as feathers that may have allowed it to fly.

Not all birds fly.
Then what do they do?
Ostriches (one of the oldest bird species) have very strong legs and can run very fast.
Penguins have dense feathers and a waterproofing that allow them to swim underwater very efficiently.
Feathers are just specialized scales. They may have been developed to attract the ladies.

Birds have lighter bones. They make it much better for flying.

Ducks in the water have webbed feet; raptors (eagles/hawks) that hunt animals from the air have talons.


You are a mammal.

Your pet dogs and cats are mammals.

An elephant is a mammal and so is a whale.

When you learn about animals, the first you learn about are probably mammals.

In mammals the females give birth to young ones instead of laying eggs.

This is one special feature of mammals which distinguishes them from the other vertebrates.

There are some mammals that still lay eggs. They are the duckbill platypus

Mammals with pouches

There are special mammals that give birth to their young live, but the babies mature in pouches.

While they are in the pouch they suckle on the mother’s milk for nourishment.

Kangaroos, koalas, bandicoots, and possums are examples of mammals that have pouches.

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