How It Works-Book Of Dinosaurs

Edaphosaurus

The fi rst true

mammals began to

evolve during the

Triassic period

Triassic fi sh and

ocean reptiles lived

in the warm seas

Ivantosaurus

Diplodocus

Augustasaurus

Pliosaurus

Chasmatosaurus

Lystrosaurus

Ichthyosaurs

Cynognathus

THE PREHISTORIC WORLD

Evolution of the dinosaur world

250 to 200 million years ago

It might have been quite hot and

dry, but that didn’t stop the very

fi rst mammals and fl ying reptiles

from appearing. Trees and plants

also grew in the places we know

today as the cold and icy south

and north poles

Triassic period

How did the dinosaurs’

world evolve?

Dinosaurs roamed Earth between

230 and 65 million years ago, when our

planet was very different to today

The ultra-dr y climates of the Permian

era, and the subsequent destruction of

the ancient coal swamps that were

home to a great many Carboniferous plants,

meant that the Mesozoic (or ‘middle life’) era

signalled something of a recover y period in

Earth’s histor y. Comprising the Triassic,

Jurassic and Cretaceous periods, the Mesozoic

era was less dr y but was still swathed in high

global temperatures, and the now-empt y

ecosystems on the land were soon taken over by

evolv ing mammals and dinosaurs. Meanwhile,

beneath the oceans, new corals appeared and

various sea urchins began to diversif y and

thrive, having been almost driven to the point

of extinction at the end of the Permian era.

Some estimates put some of the more tropical

temperatures during the start of the Triassic

period (at the beginning of the Mesozoic era)

as high as 38°C (100°F), and at this point

the world’s land masses were still

combined in one large supercontinent

called Pangaea. During the Triassic

period, Pangaea gave rise to climatic

zonation, with some areas becoming extremely

dr y and others experiencing monsoon-like

conditions. As a consequence of this climatic

zonation, plants began to separate into

northern and southern realms.

By the time of the Jurassic period, global

temperatures had dropped to around 30°C (86°F)

and Pangaea had separated into northern and

southern parts. The oceans as we know them

today really started to take shape during the

Cretaceous period – so-called because of the

large chalk content in the shallow seas as a

result of the build up of algae skeletons.

Following the major extinctions at the end of

the Cretaceous period, mammals – which were

prev iously small and insignifi cant compared to

the dinosaurs – were now able to exploit many

of the vacant ecosystems and gradually come to

dominate the planet.

200 to 145 million years ago

The Jurassic period is called the ‘Age

of the Reptiles’ because it was during

this time that reptiles ruled the planet

Jurassic period

1

2

3

4