Dinosaurs and Prehistoric Life

Three hundred million years before human first stood upright, reptiles known as dinosaurs ruled supreme. Some evolved to become the largest land animals ever to walk on Earth. Other were savage predators. The dinosaurs reign ended about 65 million years ago, probably when a asteroid smashed into the earth and caused them to extinct. In the period that followed, mammals were the dominant species, evolving to produce some amazing creatures, including, eventually us.

The Beginning of life

The Beginning Life on earth began about 3,5600 million years ago. When Earth first formed, it was too hot for life to exist. The first living things were bacteria, which developed in deep-sea springs or muddy pools near volcanoes after the earth had cooled. The bacteria took their energy from chemicals in eater, and slowly developed into more complex life forms, a process known as evolution. Many new living things began to develop by 3,000 million years ago, after some early life forms found a way of getting energy from sunlight and using it to make food. This process is called photosynthesis. During Photosynthesis, Plants release the gas oxygen. The first animals probably looked a little like tiny tadpoles, They lived in the shallow seas that covered earth about 1,200 million years ago and thrived on the new supplies of oxygen in the atmosphere. Slowly, these tiny animals grew together in clusters and developed into the first sponges.

**Stromatolites** are layers of blue-green algae and rocks. These algae were among the earliest living things to make food by photosynthesis.

Giant Forest and Insects

Plants began to grow on land around 475 million years ago. These plants lived in swamps and on the muddy shores of rivers. They probably had a waxy coating to stop the salty waters and the sun from drying them out. Plant gradually developed roots to reach water underground. They soon spread beyond the shores and began to the land green. Early plants were able to grow so big because of the climate long ago. In many places the air was damp , rather like it in tropical jungles today. As plants crowded together, they grew taller and taller as they competed for the light. Plants in the great early forests included huge horsetails, club mosses and ferns up to 50 meters tall, That is as high as 10 double Decker buses stacked on top of each other. The first insects were probably the bristle tails, which were the size of the a large prawn.. they had no wings and scurried about the ancient swamps on little legs, They used their bristles to sense movements in the air that warned them a predator was about. They had claws on their mouth-parts that they used to feed on plants and waste.

These ferns were common in the Carboniferous and Permian periods between 300 and 270 million years ago. While they had fern-like leaves, they produced seeds rather than spores. This 300 million year old fern is in an ironstone concretion. Photographed at the State Museum, Pennsylvania, USA.

Fossil dragonfly. A fossilized dragonfly preserved in rock. Fossilization occurs when an organism is buried and its body structures are slowly replaced by minerals, leaving an impression in the rock. Dragonflies are large carnivorous insects which catch other insects in mid-flight. Insects made their first appearance in geological history in the Devonian period, between 395 and 345 million years ago. This dragonfly lived in the Upper Jurassic period, 140 million years ago. The fossil comes from Kimmeridge, Solnhofen, Germany.

This giant swampy forest is from about 300 million years ago.

Rise of the Reptiles

The first reptile was probably Hylonomus, which lived 315 million years ago. Hylonomus was 20 centimetres long and looked rather like a modern lizard. Reptiles like these evolved from a group of amphibian-like tetrapods that laid their eggs on land. Inside the eggs,the young fed on yolks,which made them strong and more likely to survive. Reptiles soon became the dominant species on land. Some early reptiles lived permanently in water. The plesiosaurs had large paddle-like legs for moving through the water and long necks for reaching out to catch fish. Ichthyosaurs looked more like large, toothy dolphins. they were swimming in the oceans at the same time as dinosaurs were living on the land.

**Hylonomus** used its small sharp teeth to eat millipedes and early insects.

The group of reptiles known as **Pareiasaurs** had plates of bony Armour over their bodies. They lived about 260 million years ago. One type of pareiasaurs was **Scutosurus** which means “shield lizard.”

**Dimentrodon’s** spiny sail probably helped it to warm up and cool down.

**Ichthyosaurs** were sleek, fast-swimming reptiles.

Dawn of the Dinosaurs

The first dinosaurs developed from other reptiles from other reptiles about 230 million years ago. At this time, the world looked very different. There were no birds or mammals, and, although there were ferns and trees, there were no grasses or flowering plants. Vast areas were desert, Dinosaurs dominated the world for 150 million years. Dinosaurs lived on land. Some reptiles did live live in the sea, including Plesiosaurus, which was not related to dinosaurs. This large carnivorous animal had along neck and sharp teeth to catch fish. Other reptiles, such as the Pterosaurs, could fly. They had wings made of skin, similar to those of bats. Some dinosaurs might have hunted in packs, working together in order to catch and bring down larger dinosaurs. Their are several theories about why dinosaurs died out about 65 million years ago. The main one is that a giant asteroid crashed into earth around this time. The impact would have created dust, fires, tsunamis, (giant waves) and volcanic eruptions that caused a huge change in planet”s climate. it seems likely that the wold became freezing cold, and the dinosaurs simply could not survive in the icy conditions.

**Brachiosaurus** was one of the largest sauropods-gigantic, slow-moving plant eaters. Sauropods included some of the biggest land animals of all time.

**Plesiosaurus** lived in the sea and could grow upto to 12 meter long.

**Stegosaurus** used its spiked tail for defense and beaked mouth to bite off plants to eat.

**Gallimimus** was upto 6 meters long and about 3.5 meters tall.

**Argentinosaurus** grew to over 35 meters long. Even so, it was prey to Giganotosaurus.

**Tyrannosaurus Rex’s** teeth could be up to 30 centimetres long.

**Triceratops** used its horns for defense.

Early Birds

Scientists believe that birds developed from dinosaurs. They have discovered the fossil remains of feathered dinosaurs that many people believe are descended from dinosaurs. Archaeopteryx is the oldest known bird in the world. It flew in ancient skies about 150 million years ago. It was a meat – eating bird about the size of a cow that probably flew fairly short distances at a time. It had feathers like bird, but it also had teeth and clawed hand rather like a dinosaur.

The largest of the prehistoric birds was **Aepyornis**, also called the **Elephant bird**.

The Rise of Mammals

The 1st mammals developed almost 200 million years ago. During the time of the dinosaurs, mammals were small, furry creatures. They looked rather like the rats and shrews of today, and they ate insects. They scurried around at night and probably lived in holes underground to hide from dinosaurs. After the dinosaurs died out, many new kind of mammals slowly developed.

The 1st mammal was probably **Megazostrodon,** a small rat like animal.

From Apes to Humans

Primates are a group of mammals that includes apes, monkeys and humans. The 1st primates lived on earth about 50 million years ago, but they looked rather like squirrels. Over million of years, different kinds of primates evolved. Between 20 and 10 million years ago, giant apes were common in Africa. The Neanderthals were an ancient human species that lived in Europe and Asia from about 300,000 to 30,000 years ago, when they became extinct. Long ago, there were other human species, but all of these died out. One was Homo erectus, perhaps our earliest human ancestor. Homo erectus first appeared almost 2 million years ago and died out 100,000 years ago. The 1st people depended on wild plants and animals for food. They used sharp sticks to spear animals or knock them from trees. Their uses of tools and their ability to work together were two of the things that made early humans so successful. Around 5,000 years ago, people began to write and read. This was the end of the prehistoric period because started to write down their history.