The Stories Fossils Tell
Can you name the 4
types of Fossils ?
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Name the 4 types of Fossils
 Mold
 Trace
 Casts
 True
form
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Describe how Mold
Fossils are formed.
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Mold Fossils
-are usually formed in sediment
-organisms like shells, leaves or bones, are
covered with mud
-over time mud hardens
-water enters mold and dissolves dead
organism
-mold fossils are HOLLOW on the inside
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Describe how Casts
Fossils are formed.
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Casts fossils
-need a mold fossil first
-after organism dissolves and leaves
an empty space
-the empty space fills with minerals –
-as time passes it hardens to form a
cast fossil
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Describe how Trace
Fossils are formed.
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Trace Fossils
-are markings left by animals
-examples include leaf prints, footprints,
eggs and nests
-Trace fossils are good for scientists to
use to understand animals’ BEHAVIORS
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Fossil footprints have yielded information about:
Speed and length of stride
whether they walked on two or four legs
the bone structure of the foot
stalking behavior (a carnivore hunting a herd of
herbivores)
the existence of dinosaur herds and stampedes
how the tail is carried (few tail tracks have been found,
so tails were probably held above the ground)
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Describe how True Form
Fossils are formed.
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True Form Fossils
True Form fossils are formed when the animals
soft tissues or hard parts did not decay over
the years because they are trapped in sap that
hardens to become amber.
This evidence gives scientists the
BEST observation of past plants
and animals.
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Fossils start out as living things.
The organism can be either a plant or an animal.
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When the organism dies . . .

The soft parts that are
exposed to air
decompose quickly.

Hard parts like bones,
shells, or wood, don’t
decompose as
quickly. They have
the greatest chance
of becoming a fossil.
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The organism may be buried in layers
deep in the earth. These layers might
be composed of mud, lava or water.
Sediments
Basalt
Fossil layer
Sandstone
Basalt
Coal
Sedimentary Rock
Basalt
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Scientists sometimes dig in the
Earth looking for fossils.
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How do fossils help us learn about
the past?
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Thinking like a paleontologist
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Let’s practice making inferences
about living things.
Would the tree
live in this
environment?
Look at these
pictures of things
that come from a
tree. Make a
prediction about the
environment where
you would find this
tree.
… or, would
the tree live in
this
environment?
This is more difficult isn’t it? Why?
What would help you decide on the
correct environment?
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Can you be a paleontologist?
This is the environment where
you are looking for fossils.
Here in an example of the kinds of
fossil your team has found. What do
you think the environment might have
been like in the past?
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Let’s try another example!
You just found the plant fossils, on the left, in an area where it is now
hot and dry like the picture on the right. What predictions can you
make about what the environment might have been like in the past?
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“Once Upon a Time” is not just
for fairy tales.
Wooly Mammoth
Asian Elephant
How are these two animals the same?
How are they different?
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The wooly mammoth is the
ancestor of the modern Asian
elephant.
Wooly Mammoth
Asian Elephant
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Once Upon a Time – A Look at the
Horse
Horse B
Horse A
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Change Over Time – A Horse’s
Foot
Note how the distance of the wrist bones from
the ground changes. What else has
changed?
wrist
Adapted from Florida Museum of Natural History. For more information visit their website at
http://www.flmnh.ufl.edu/natsci/vertpaleo/fhc/relatives1.htm
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Let’s Look More Closely
How have the bones in horse feet changed over time?
Why might this have happened?
Adapted from Florida Museum of Natural History. For more information visit their website at
http://www.flmnh.ufl.edu/natsci/vertpaleo/fhc/relatives1.htm
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Wrap-Up

Fossils are formed under
very special conditions.

They give us clues about
what life was like long
ago.

Fossils also give us clues
about the environment
from a long time ago.

They help us understand
that plant and animal
species change over
time.
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Group 1, group 3, group 4,
group 2
Group 2 is the youngest.
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a. Rivers deposited the shells
b. The region was once under an ocean environment
c. Early Native American left them there.
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b.The region was
once under an ocean
environment
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