Evolution of prehistoric animals
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The Earth formed from a cloud of dust and gases drifting through space about 4.6 billion years ago. However, the first known life forms- bacteria and blue-green algae didn't appear until about 3.4 billion years ago and it was only about 700 million years ago that complex plants and animals began to develop. We know prehistoric animals existed because some of their remains have been preserved in rocks as fossils. These fossils reveal the shape and size of the animals. From this, scientists can work out how they lived, what they ate, and why most are no longer around.
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[edit] Armoured Creatures
The first living things appeared about 3.4 billion years ago. We don't know much about them because their soft bodies usually decayed rather than being fossilized after death. The greatest evidence available that they existed at all is the presence, later and to this day, of more complex life forms, which could have only evolved from simpler organisms. About 600 million years ago, animals began to develop shells or other hard coverings, and these hard parts were often preserved as fossils. Trilobites were among the earliest of the armoured creatures. They looked rather like woodlice and lived mainly on the sea bed. Corals and many kinds of shellfish lived with trilobites. Huge sea scorpions, up to about 2m long, and other predators, arose to feed on smaller animals.
[edit] Out of the water
The first animal with backbones were fish, which appeared about 500 million years ago. Many of them had bony armour to protect them from predators. The earliest prehistoric animals all lived in the sea, but they gradually spread into fresh water and then onto the land. The amphibians were the first backboned animals to move on to the land. These early amphibians were rather like fish with stumpy legs that could only just lift their bodies off the ground. Some of them looked like big newts or salamanders. The early amphibians, as today, lived in damp places and, just like today's frogs and toads, they had to go back to the water to breed. One group of amphibians started to change: their skins got thicker, allowing them to retain moisture when out of water, and they laid eggs with tough shells, which did the same for the developing embryos whilst also protecting them from being damaged. These animals became the first reptiles.
Being the first, and thus having no competition, the reptiles quickly "cornered the market" on land, establishing a foothold for life there that it has not given up to this day. The new land-dwellers could hunt in the sea, whilst sleeping and raising their offspring in the relative safety provided by the land. But as evolution turned several species into many, the land developed unique dangers of its own.
 DIPLOCAULUS-an amphibian from the Permian period, was a pond dweller. His head shape would have made him hard to swallow, and allowed him to maneuver well in water. |
[edit] Taking to the skies
Some reptiles, called pterosaurs, spurred by evolutionary changes, eventually learned to fly. Others went back to the sea, becoming the prehistoric equivalent of modern dolphins. The best known prehistoric reptiles were the dinosaurs, which "ruled" the earth for over 100 million years during the Triassic, Jurassic and Cretaceous periods. Many small, rat like mammals wandered over the land at the same time as dinosaurs. Most probably fed on seeds and tubers, and were relatively successful. But it was only when the dinosaurs died out, about 70 million years ago, that mammals really had a chance to thrive.
 Meganeura was like a giant dragonfly, with a wingspan reaching to about 75 centimeters. It probably grew large because of the warm Carboniferous forest, and the abundance of oxygen in the air. |
 Quetzalcoatlus was the largest pterosaur. It lived in Europe about 150 million years ago and a wingspan of at least 12 meters (almost 5 times bigger than our largest bird). Its loose throat pouch may have held fish. |
[edit] "Experimental" mammals
As nature experimented with different shapes and sizes, many very strange prehistoric mammals appeared. Baluchitherium was a giant, giraffe-shaped rhinoceros that lived in Asia between 20–30 million years ago. With its huge head carried 8m above the ground, it was probably the largest mammal ever to live on land. Most of these 'experimental' mammals died out completely, but some of them survived and gradually evolved into the mammals that we see around us. Like the reptiles before them, some returned to the sea and became whales and seals and some developed wings and learned how to fly, becoming modern bats.
 Smilodon (sabre-toothed cats)-was one of the sabre-toothed cats of the Pleistocene period. They had massive fangs, about 15 centimeters long, and huge neck muscles to power their jaws. Like modern big cats, they probably killed via strangulation |
[edit] Mammals in the ice age
During the last 2 million years, there have been several very cold periods called ice ages. Many northern parts of the world were covered with ice. Most animals moved south to avoid the cold, but some managed to survive close to the ice because they were able to grow thick coats, like the woolly rhinoceros and the woolly mammoth. These cold-climate mammals died out when the climate began to warm up about 10,000 years ago and new species evolved to replace them. The emergence of mankind may have also proved a factor, but this isn't known for certain.
[edit] Timeline
| Period | Animals | Year |
|---|---|---|
| Precambrian | Jellyfish, Worms | 3500 mya (mya - million year ago) |
| Cambrian | Sellfish, corals, jawless fish | 570 mya |
| Ordovician | 505 mya | |
| Silurian | First land plants | 438 mya |
| Devonian | Insects, spiders | 408 mya |
| Carboniferous | First reptile | 360 mya |
| Permian | 286 mya | |
| Triassic | Dinosaurs, mammals, frogs | 245 mya |
| Jurassic | First birds | 208 mya |
| Cretaceous | Snakes, first mordern animals | 144 mya |
| Palaeocene | Owls, shrews | 65 mya |
| Eocene | Horses, dogs, cats, elephants, rabbit | 58 mya |
| Oligocene | Deer, pigs, monkeys, rhino | 37 mya |
| Miocene | Mice, rats, apes | 24 mya |
| Pliocene | Cattle, sheep | 5 mya |
| Pleistocene (ice age) | Homo sapien | 2 million years ago |
| Precambrian 3500 MYA | Precambarian |
| Paleozoic 570-245 MYA | Permian, Carboniferous, Devonian, Silurian, Ordovician, Cambrian |
| Mesozoic 245-65 MYA | Cretaceous, Jurassic, Triassic |
| Cenozoic 65-0 MYA | Pleistocene (ice age), Pliocene, Miocene, Oligocene, Eocene, Palaeocene |
