Animals of the past
The most famous prehistoric animals have got to be the
dinosaurs—but they lived many hundreds of thousands
of years after the first life-forms appeared on Earth. It is
thought that life first appeared on Earth around
3.8 billion years ago. They were small,
single-celled organisms called
prokaryotes. Some prokaryotes
survive today in the form
of cyanobacteria.
LIVING WORLD
The first forms of life
appeared on Earth:
simple, single-celled
prokaryotes.PRECAMBRIAN
4.6 BYA545 MYAThe first multicelled
and hard-bodied life
developed, including
mollusks and arthropods
such as trilobites.CAMBRIAN
545490 MYAThe first crustaceans
and jawless fish
evolve.ORDOVICIAN
490445 MYAEvolution of the first
fish with jaws, and
giant sea scorpions—
the ancestors of
modern arachnids.SILURIAN
445415 MYAThe “Age of Fishes,”
when fish diversified
rapidly. The first
amphibians evolved
from fish, becoming
the first vertebrates
to live on land.DEVONIAN
415355 MYAFlying insects
and amphibians
lived in swampy
forests during
this warm
period, but
reptiles ruled
the land.CARBONIFEROUS
355290 MYATIMELINE OF PREHISTORIC LIFE History is divided into different periods of time.^ MYA = million years ago.
WHAT WAS A DINOSAUR?
The word “dinosaur” means “terrible
lizard.” These reptiles ruled the Earth for
more than 160 million years until around
65 million years ago. But not all dinosaurs
were terrible: many were herbivorous, not
carnivorous, and while many were huge
and ferocious, there were also some that
were no bigger than a chicken.In Precambrian times,
prokaryotes grew in colonies that
spread out like mats, absorbing
sunlight so they could photosynthesize.
Billions of years later, their fossilized
remains still exist. These stony
platforms are called stromatolites,
and some can be found off the
coast of northwest
Australia.7
/ (^7)
DINKY DINOSAUR
The plant-eating Lesothosaurus is
thought to be the smallest dinosaur.
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