Biology (Holt)

The Fossil Record

Have you ever looked at a series of maps that show how a city has
grown? Buildings and streets are added, changed, or destroyed as
the years pass by. In the same way, fossils of animals show a pattern
of development from early ancestors to modern descendants. Fos-
sils offer the most direct evidence that evolution takes place. Recall
that a fossil is the preserved or mineralized remains or imprint of
an organism that lived long ago. Fossils, therefore, provide an
actual record of Earth’s past life-forms. Change over time (evolu-
tion) can be seen in the fossil record. Fossilized species found in
older rocks are different from those found in newer rocks, as you
can see in Figure 7.
After observing such differences, Darwin predicted that interme-
diate forms between the great groups of organisms would eventually
be found. Since Darwin’s time, many of these intermediaries have
been found. For example, fossil intermediaries have been found
between fishes and amphibians, between reptiles and birds, and
between reptiles and mammals, adding valuable evidence about the
fossil history of the vertebrates.
Today, Darwin’s theory is almost universally accepted by scien-
tists as the best available explanation for the biological diversity on
Earth. Based on a large body of supporting evidence, most scien-
tists agree on the following three major points:

1.Earth is about 4.5 billion years old.

2.Organisms have inhabited Earth for most of its history.

3.All organisms living today share common ancestry with earlier,
simpler life-forms.

Evidence of Evolution

SECTION 2 Evidence of Evolution 283

Section 2

Objectives

Describehow the fossil

record supports evolution.

Summarizehow biological

molecules such as proteins

and DNA are used as

evidence of evolution.

Inferhow comparing the

anatomy and development

of living species provides

evidence of evolution.

Key Terms

paleontologist

vestigial structure

homologous

structure

Figure 7 Fossils.Fossils

of early multicellular life-forms,

such as the crinoid, occur in

800-million-year-old rocks

found in Indiana. Fossils

of the pterodactyl, an extinct

reptile, occur in 140- to

210-million-year-old rocks.

Crinoid Pterodactyl

7A

9A

7A