Page 14 - The Dinosaur Book and Other Wonders of the Prehistoric World (DK-Smithsonian)

Types of

Introduction fossils

Most of what we know about
prehistoric life comes from fossils—

the remains of ancient organisms
entombed in rock. The study of
fossils and the sedimentary rocks
containing them has enabled
scientists to piece together a
record of life on Earth.

Natural cast
Fossils can form in various ways. Some
of the most common fossils are casts—
replicas of a whole body or a body part that
formed from minerals building up inside a cavity.
This ammonite cast formed when minerals built up inside
the animal’s spiral shell after its soft inner tissues decayed.
Ammonite cast

How fossils form

Only a tiny fraction of the
animals that lived in the
past left fossils behind.
Fossils of land animals
are especially rare because Thousands
of years later,
they form only in unusual The body of layers of mud
circumstances. The animal a drowned The flesh and sand
must die in a place where Tyrannosaurus slowly rots have buried
its body is undisturbed sinks to the away, leaving the skeleton.
and scavengers can’t easily muddy floor behind hard
of a delta,
consume it. Mud or sand where a river body parts
needs to cover the remains, meets the sea. such as bones
and teeth.
which must stay buried for
millions of years as they
slowly turn to rock.
Geological forces must
then bring the fossil back
to the surface, where it Dinosaur drowns Flesh decays Sediment builds up
can be found.
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