Wikijunior:Dinosaurs/Prehistoric Creatures Before the Dinosaurs

The Earth existed for millions of years before the time of the dinosaurs. This time is known as the Paleozoic Era while the dinosaur time is known as the Mesozoic Era.

There were strange and wonderful creatures living in each of the seven periods of the Paleozoic Era: Precambrian, Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian.

The types of creatures that lived then were reptiles, amphibians, fish, arthropods and mammal-like reptiles.

In the late Permian a big extinction wiped out 90% of life on Earth. It all started 543 million years ago. Before this time there was a time called the Precambrian, it lasted for four billion years. The Permian extinction that wiped out 90% of all life on Earth gave the reptiles space to spread out quickly and evolution led them to develop into dinosaurs over millions of years.

The Precambrian period
This period was the period from which the Earth was first formed. It lasted billions of years and for almost all of it there was no life. However, for reasons we don't yet understand life suddenly began. It started out only as small, one-celled creatures. Soon they evolved into more complicated creatures at the start of the Cambrian period.

The Cambrian period
The Cambian started 543-490 million years ago. At this time life developed in the seas, not on dry land.

Some of the first creatures to live on Earth in the Cambrian were haikouichthys, trilobites, jellyfish and a creature called Anomalocaris. Haikouikthys were 2.5 centimeters (1 inch) long. They had a primitive backbone, scavenged meat and lived 535 million years ago in the area now known as China. Haikouicthys also was one of the first vertabrates

The trilobites were the Paleozoic's big success story; they could be 5 millimeters- 80 centimeters long (0.2-32 inches). The trilobites were scavengers too and they lived 520-248 million years ago in the Cambrian period to the Permian period. They could be found all over the world. They are known as the beetles of the Paleozoic.

The Anomalocaris was two meters (6.5 feet) long and it had a hard shell that could split off if it was bent too far. Anomalocaris was a carnivore. Anomalocaris lived in the areas now known as North America, China and Australia. Anomalocaris means strange crab.

The Ordovician period
The Ordovician Period lasted from about 510 to 440 million years ago. The land of the super-continents did not support life, so all the creatures lived in the oceans and seas. Some creatures that developed in the Ordovician had backbones and were the first vertebrates. Some common non-vertebrate animals from this period were corals, sea urchins, trilobites, sponges, arthropods and jellyfish.

One creature of the Ordovician Period was called Cameraceras. Cameraceras was a cone like creature that was 10-11 meters (33-36 feet) long. It lived in the ocean and is related to the modern day squid. Another creature of the Ordovician is Megalograptus, Megalograptus was one metre(3.25 feet) long. Megalograptus was carnivorous and was found in the area now known as North America.

The Silurian period
The Silurian started 433-417 million years ago. The first plants started to evolve, life finally reaching land. The land creatures were similar to today's millipedes and centipedes. As the plants died and the bugs and fungus decomposed them, the first dirt started to arrived. Silurian fish like cephalaspis were bony-headed fish. While life on land was going slowly, the water saw the arrival of massive arthropods like Brontoscorpio (meaning thunder scorpion), which was 99cm long. The fish back then had a good reason to have large head armour: since bones were still primitive, the fish used bony plates to protect their brain. Fish like cephalaspis had a very good sense of navigation and memory. Although there were benefits to having head wear, there was also the down side the boniness slowed the fish down, making them vulnerable to attack by Brontoscorpio.

The Devonian Period
During the Devonian Period, fish may have evolved feet and lungs, and became the first amphibians and the first vertebrate to walk on land. The Devonian also saw the success for the placoderms, a group of bony fish with scissor-like jaws and big bony teeth. The placoderms eventually became extinct at the end of the Devonian. On land, plants started to get big and turned into the first trees and since there would be nothing to eat the trees for the next hundred million years the trees turned into vast forests.

The Carboniferous period
This period was a time were giant insects ruled. The earth's oxygen content was 20% higher than today, and this probably explains why they got so big. As well as giant insects, many other huge creatures roamed the land, such as Eryops, a large carnivorous amphibian.

The Permian Period
Mammal-like reptiles started evolving such as Gorgonops, Dimetrodon and Lystrosaurus. Near the end of the Permian the earth's land formed the super continent Pangea, and started to dry up causing creatures like Scutosaurus to search the planet for water. The end of the Permian also saw an extinction worse than the K-T Extinction. The K-T extinction killed 75% of life on earth, but this extinction eventually caused the extiction of 90% of the life on earth.