The First Animals on Earth

Worms were among the first animals found around the world
Worms are soft-bodied animals that have long bodies shaped rather like a tube. They first evolved around 600 million years ago and lived in seas across the world. Ottoia (oh-toe-ee-ah) lived in what is now Canada. It lived in the mud of the sea bed, searching for tiny animals and plants. 


Trilobites were the most numerous arthropods
Trilobites first lived about 550 million years ago. Soon there were more trilobites than any other sort of creature. The word “trilobite” (try-low-bite) means “three parts”. It was given to creatures such as Conocoryphe (kone-oh-corr-eeff) because the body is always divided into three parts, a head, a body and a tail.


Trilobites had jointed bodies
Trilobites had a tough, hard covering all over their bodies. This protected them from injury. The outer shell was jointed wherever the animal needed to be able to move. Together with other animals with jointed outer shells – such as modern crabs – the trilobites belonged to a group of animals called the arthropods (arr-throw-pods).


Pterygotus was the first large hunter
Growing to be over 2 metres long, the same size as an adult human, Pterygotus (terr-ee-got-uss) was a ferocious hunter. It had powerful pincers to catch prey and could move quickly by beating its tails against the water. It belonged to a group of animals called sea scorpions. Sea scorpions lived between 500 and 250 million years ago.


Ammonites had curled shells
Scientists have found thousands of fossils with curly shells. The animal that lived inside the shell is called an ammonite (amm-oh-nite). Most of the shell was filled with gas to help the creature float in the water. Ammonites existed for millions of years, but they all died out around 65 million years ago.


All animals with backbones are related to each other
Many different sorts of animals – such as fish, reptiles and mammals – have backbones. A backbone is a series of bones inside which run nerves to carry messages to and from the brain. Scientists believe that all these animals are descended from a single type of animal. The earliest known creature with a single spinal nerve was Pikaia (pye-kee-ah). It lived about 530 million years ago in seas covering what is now North America.

Quiz
1. Which animals are shaped like a tube?
2. What does the name “trilobite” mean?
3. When did sea scorpions live?
4. What filled most of an ammonite shell?
5. What made Pikaia special?