5 3 3 paleontology digging for dinosaurs and more

What are some things you can think of, other than dinosaur replica bones, that might be made in a mold3. To make replica bones, workers create a mold of each fossil bone.. The Finished

Suggested levels for Guided Reading, DRA, ™

Lexile, ® and Reading Recovery ™ are provided

in the Pearson Scott Foresman Leveling Guide.

Scott Foresman Reading Street 5.3.3

ISBN 0-328-13538-0 ì<(sk$m)=bdfdih< +^-Ä-U-Ä-U

Genre Comprehension

Skills and Strategy Text Features

Expository

nonfi ction

• Fact and Opinion

• Cause and Effect

• Predict

• Captions

• Headings

• Glossary

Life Science

Digging for Dinosaurs and More

by Laura Johnson

Paleontology:

Suggested levels for Guided Reading, DRA, ™

Lexile, ® and Reading Recovery ™ are provided

in the Pearson Scott Foresman Leveling Guide.

Scott Foresman Reading Street 5.3.3

ISBN 0-328-13538-0 ì<(sk$m)=bdfdih< +^-Ä-U-Ä-U

Genre Comprehension

Skills and Strategy Text Features

Expository

nonfi ction

• Fact and Opinion

• Cause and Effect

• Predict

• Captions

• Headings

• Glossary

Life Science

Digging for Dinosaurs and More

by Laura Johnson

Paleontology:

1 Using a graphic organizer like the one below, record

three facts about dinosaurs in the left-hand column Then write your opinion of this information in the right-hand column

2 What do you think paleontologists will do in the

future? On what facts are you basing your prediction?

3 What are some things you can think of, other than

dinosaur replica bones, that might be made in a mold?

4 What question would you most like to ask a

paleontologist? Why?

Reader Response

Vocabulary

erected

foundations

mold

occasion

proportion

tidied

workshop

Word count: 1,597

Paleontology:

by Laura Johnson

Digging for Dinosaurs and More

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3

What Is Paleontology?

Paleontology is the study of living things that died before people kept records If none of these living things are around today, how do we know they once lived? Through the study of fossils!

Fossils are preserved, or saved, remains that offer proof of plant or animal life from long ago There are two types of fossils One type is body fossils

These are remains of body parts, such as bones, that have been preserved over the years The second kind

is trace fossils These are clues left behind by animals, such as footprints, tracks, and bite marks

Bones are examples of body fossils Footprints and tracks are examples of trace fossils

From Bones to Fossils

Fossils can form when plants and animals die and

fall to the ground Plants and animals die all the

time, but fossils are rare This is because conditions

must be perfect for a fossil to form

Let’s look at how a fish can become a fossil

1 First, the fish dies in a place where there is little

air, such as the bottom of the ocean Or it dies at

the surface and sinks to the bottom

2 Minerals in the water work their way into the

fish’s bones and body parts After a long time, all

the bone in the skeleton is replaced by minerals

that harden and turn into stone

3 Layers of mud, sand, clay, and rock build up on top of the skeleton Their weight presses down Over many years, the pressing causes the layers to stick together and form rock

4 The fish is now preserved in solid rock If the fossil

is discovered and studied, it will provide clues about the fish that once lived

Paleontologists at Work

Paleontologists are scientists They study

prehistoric life by examining fossils They know

how to “read” fossils By studying a fossil, a

paleontologist might be able to tell the size of an

animal, where it lived, what it ate, and more

The first thing paleontologists do when they find

a fossil is map the area around it This area is called

the excavation, or digging, site They make a grid, a

type of graph, of the site to keep track of the fossils

Recording the exact location

of each fossil on a site map is

extremely important.

7

Fossils can be fragile Paleontologists often brush them with glue to give them strength and prevent chipping When a fossil is ready to be sent to a

workshop, it’s wrapped in paper or foam and packed

in bags Larger fossils are wrapped in casts similar to the ones that doctors put on broken arms or legs

Often the fossils sent back to the workshop have bits of rock still stuck to them Paleontologists at the workshop use tools to remove the bits of rock

Then the fossils are tidied up Paleontologists tidy

them by removing even tinier bits of rock They use microscopes to help them avoid chipping the fossils

Protective gear prevents injury from flying slivers

of rock.

Excavation tools range in size from tiny drills to heavy jackhammers Very large jobs may require cranes and explosives.

Preparing Fossils for Display

Putting together an animal’s fossils to create a

museum exhibit is very difficult! Most fossils are too

delicate to be put on display Instead, replica, or

look-alike, bones are used

To make replica bones, workers create a mold of

each fossil bone The mold is created by painting a

bone with layers of a rubbery material After the

material dries, workers peel it away from the bone

Next, the mold is filled with either plastic or

plaster When this material hardens, the mold is

peeled away There is now a replica of the bone

The replica is painted to look like the original fossil

Sometimes, if a fossil skeleton is not complete,

workers need to create replacement parts The

replacement parts must be in the right proportion to

the rest of the bones

When the painting is finished, the replica bones

are ready to be connected in the shape of the

animal Workers build a frame to support the rebuilt

skeleton The frame is arranged to show how the

animal stood

Once the frame is erected, paleontologists lay

out the replica bones and arrange them correctly

Starting at the foundation, the bones are attached

to the frame Then the model is ready for display!

A worker creates a mold of a dinosaur skull.

The Finished Product: Sue

One of the most famous fossils is a Tyrannosaurus

rex named “Sue.” Sue was named after fossil hunter

Sue Hendrickson She discovered the fossils in 1990

Sue is the largest, most complete, and best preserved

Tyrannosaurus rex yet discovered Of the more than

250 bones in a Tyrannosaurus skeleton, only one

foot, one arm, and a few ribs and back bones are

missing from Sue

It took six paleontologists seventeen days to

excavate the fossil of Sue Then, it took a group of

ten workers two years to clean the bones and piece

them together!

You might be asking, do paleontologists ever

make mistakes when they make models of extinct

dinosaurs? Sometimes they do The first replica made

of a dinosaur was a model of an Iguanodon When

scientists first pieced its bones together, they decided

that one of the bones was a horn Years later, other

scientists realized that that bone was not a horn It

was a spike on the dinosaur’s thumb! On another

occasion, the head of one kind of dinosaur was

attached to the body of a different dinosaur

11

Sue can be seen at the Field Museum in Chicago, Illinois.

Always Learning

Paleontologists study chemistry, biology, zoology

(the study of animals), and geology (the study of

Earth) They also study math and computer science

Paleontologists often learn several languages This is

because their work takes them all over the world!

There are only about one hundred dinosaur

paleontologists in the world today, but they discover

an average of seven new kinds of dinosaurs a year!

As new fossils are collected and studied, what they

know about dinosaurs changes

For example, paleontologists once thought that

Tyrannosaurus rex was the largest meat-eating

dinosaur Then, in 1995, fossils were found in

Argentina of a meat-eating dinosaur that was even

larger than Tyrannosaurus rex Scientists named

this dinosaur Giganotosaurus

Giganotosaurus and

Tyrannosaurus rex lived

at different times and in

different places, so they

would never have met

Giganotosaurus was bigger than Tyrannosaurus rex

However, scientists think it had

a smaller brain, less powerful jaws, and narrower teeth than Tyrannosaurus rex.

Tyrannosaurus rex was

a huge meat-eating dinosaur For years, scientists have been puzzled about its tiny arms Its arms were

so short that they couldn’t even reach its mouth!

More Recent Discoveries

Paleontologists have known for a long time that

most plant-eating dinosaurs were bigger than their

meat-eating relatives For a while they thought that

the largest plant-eating dinosaur was Brachiosaurus

This huge dinosaur was about 90 feet long and

weighed roughly 75 tons In 1979 fossil hunters in

New Mexico discovered fossils of an even larger

plant-eater They named it Seismosaurus, meaning

“earth-shaker.” This dinosaur may have been 120 feet long

and may have weighed nearly 90 tons!

Using computer technology, some paleontologists

have decided that Seismosaurus could move its tail

faster than the speed of sound There is one thing

we know for sure about the tail of Seismosaurus: It

was huge!

It would take five school buses lined up end-to-end

to equal the length of Seismosaurus!

15

In 1996, scientists

in China found a fossil skeleton of a small dinosaur that they named

Sinosauropteryx The fossil

had feather-like markings

Up until then, scientists thought all dinosaurs were cold blooded The discovery

of what might be feathers

on the Sinosauropteryx

fossil meant that some dinosaurs may have been warm blooded Warm-blooded animals include birds and mammals If dinosaurs were warm blooded, then they would have been able

to adapt to changes in temperature For cold-blooded animals, such as frogs, lizards, and snakes, the temperature of their blood changes with the temperature of their surroundings, so they can easily get too hot or too cold

Sinosauropteryx was about the size

of a turkey.

Recent discoveries have led scientists to change

their minds about how dinosaurs behaved

Paleontologists once thought that dinosaurs did

not form groups or care for their young However, a

set of newly discovered fossil footprints shows that

some dinosaurs lived in groups and took care of their

young

These footprints were found in Colorado and Texas

They show both small and large footprints made by the

Apatosaurus The prints seem to show that parents and

young dinosaurs traveled together

Sue Revisited

Computer images of the inside of Sue’s skull show very large olfactory bulbs These bulbs control an animal’s sense of smell Scientists used to think that

Tyrannosaurus rex had a poor sense of smell But the

images suggest Sue had a good one!

Most scientists believe that Tyrannosaurus rex was

mainly a hunter But this new information suggests that it might also have been a scavenger Scavengers are animals that eat dead and decaying creatures

So did Sue spend most of her time hunting or scavenging? New information often presents more questions than answers!

Apatosaurus lived in what is now Colorado and Texas.

Most dinosaurs lived in hot climates, but new

discoveries have shown that this wasn’t true of all

dinosaurs In 1985 fossils of eight types of dinosaurs

were found in Alaska Alaska is very cold today, so

scientists wondered how dinosaurs could survive

there However, when they studied the fossils of

plants as well as of dinosaurs, they discovered that

Alaska was much warmer millions of years ago

There are still some questions Though Alaska was

warmer then than it is today, it was still cooler than

places where most dinosaurs lived Scientists are still

trying to find out how Alaska’s dinosaurs adapted

In 1985 many dinosaur bones were found in Alaska

19

What Happened to the Dinosaurs?

There are several theories about what caused dinosaurs’ extinction At different times scientists thought that volcanic eruptions, diseases, or a gradual cooling of Earth might have been the cause Now, however, most scientists believe that the

effects from a huge asteroid hitting Earth caused the dinosaurs to become extinct

You’ve now learned about how paleontology works and what paleontologists do You’ve also read about the new ideas that have developed as new dinosaur fossils have been found One thing is for sure: We will keep learning more about dinosaurs as scientists find more dinosaur fossils!

A huge asteroid hitting Earth may have been responsible for the extinction of dinosaurs.

erected v to have been

put up straight; to have

set upright

foundation n the part on

which the other parts rest

for support; base

mold n a hollow shape

that you pour soft or

liquid material into that

gives its shape to the

hardened material

occasion n a particular

time

proportion n a proper

relation between parts

tidied v to have put in

order; to have made neat

workshop n a building or

area where work is done

1 Using a graphic organizer like the one below, record

three facts about dinosaurs in the left-hand column Then write your opinion of this information in the right-hand column

2 What do you think paleontologists will do in the

future? On what facts are you basing your prediction?

3 What are some things you can think of, other than

dinosaur replica bones, that might be made in a mold?

4 What question would you most like to ask a

paleontologist? Why?

Reader Response

Vocabulary

erected

foundations

mold

occasion

proportion

tidied

workshop

Word count: 1,597