EARTH AND ENVIRONMENT THROUGH TIME - EES 1005

LABORATORY SIX

FOSSILS AND FOSSILIZATION

Introduction This week you will begin working on the

fossil notebook. It will be due in 4 weeks

and is worth 25% of your grade. This is an

exciting and important part of the class

because you have a chance to carefully look

at various fossils on your own and learn more

about them. You will be answering

questions which may take some extra

thought, so it is a good idea to do as much as

possible during lab time when the instructor

can help you. No late notebooks will be

accepted.

Please handle the specimens carefully.

Inform your instructor if any of them are

badly damaged, missing, or seem to be in the

wrong box. The notebooks are to be

handwritten and drawn only.

Photograph taken by Jacqueline Wood, 2005

No photographs. Drawing is an

important method of observation in the

scientific process. You are required to use

the sheets included in the Appendix of your

lab manual. These sheets with your drawings

and answers should be put in order into a

folder and handed in on the due date

specified by your instructor. This is the only

format that will be accepted

The fossil notebook is changed

every semester, so you should be using the

most current version. Do not use old copies.

The notebook and answers contained within

it should be yours and yours alone. Should

the TA notice any discrepancies, a zero grade

will be earned for that section of the

notebook.

Photograph taken by Jacqueline Wood, 2005

Fossils

Fossils are important

in helping reconstruct the

history of life on earth. A

fossil is any reasonably

obvious trace of pre-existing

life. Usually fossils are old.

Usually they are embedded in

sedimentary rocks. Finally,

they are usually not associated

with humans.

Paleontology is the study

and interpretation of fossils.

Fossils can be useful in several

ways. Paleontologists use

fossils to help determine

ancient environments and the

ages of rock beds. A fossil

may be direct remains of a part

of an organism, such as teeth,

bones, or shells. In addition

evidence of past life such as a

footprint or a "gizzard stone"

are known as trace fossils.

When one considers the

many factors that can destroy

an organism after its death, it

seems remarkable that so

many fossils can be found.

The process of fossilization is

a rare occurrence. Chemical

decomposition, erosion,

Points to Ponder

What is a fossil?

Why are some life forms

more conducive to

fossilization?

How does fossilization

occur?

What does the fossil record

tell us?

Does the fossil record

accurately document the

history of life?

scavengers, and pressure

and temperature changes are

several processes that

decrease the odds of

fossilization occurring. The

possession of hard parts,

rapid deep burial, and

protection from bacteria

are conducive for

fossilization.

Most of the fossils

used to interpret earth

history are organisms whose

hard part (shell, bone, ect.)

have been preserved. Since

the hard parts of most

invertebrate organisms are

composed of calcium

carbonate, silica, or chitin,

and since the bones of most

vertebrates are composed

primarily of calcium

phosphate, alteration during

transportation and burial is

expected. The following

sections outlie some of the

various methods of

preservation. Note that

some fossils may be

preserved by combinations

of more than one type of

preservation.

The Fossil Record is Biased Because the fossilization process favors the preservation of marine animals with hard

parts, the fossil record gives a biased view of the history of life on earth. Insects are one of the

dominant living animal groups, however insects make up only about 1% of all the fossils.

Even animals with hard parts are subjected to destruction. They may be broken by wind and

wave action, attacked by scavengers, or turned to dust due to chemical weathering. This

causes the fossil assemblage to reflect only a small portion of the original biosphere.

We will undertake our study of fossils from a biostratigraphic approach. We will look

at the organisms beginning with the oldest ones and study their evolution. By knowing which

fossils are likely to be found in certain stratigraphic age horizons, we will be able to use these

fossils to reconstruct the history of the area in which it was found. The next few chapters are

in chronological order. This appearance and extinction of different species in the fossil record

are outlined as well as the relative abundance of each important marine organism.

Methods of Preservation

Preservation Methods

1. Unaltered remains (rare)

Soft parts - entrapment of organisms in amber or oil seeps

Hard parts - unaltered shells, bones, or teeth

2. Permineralization - Minerals deposited in pore spaces (such as in wood and bone) and

may become permineralized: also called petrification.

Skeletal material may be the original, replaced, or recrystallized.

Common permineralization agents include calcium carbonate (CaCO3), silica (SiO2),

pyrite (FeS2), and dolomite (CaMg(CO3)2).

3. Recrystallization - Original material is recrystallized into a more stable form. No new

material is added or taken away. This method of preservation is hard to identify.

4. Replacement - New material replaces the original skeleton; common replacement minerals

includes calcite, quartz, and pyrite.

Mold - skeletal hard part dissolved resulting in a hole in the rock.

Internal molds preserve the internal structure.

External molds preserve the external structure.

Casts - new material fills in natural molds, forming a replica of the original skeleton.

5. Carbonization - Heat and pressure degrade original materials leaving a thin film of carbon

in the shape of the organism, this can preserve fine details and soft parts.

6. Trace fossils - Any indirect evidence of an organism. Records behavior of organism. ex:

tracks, trails, burrows, coprolites (fossilized feces), gastroliths (gizzard stones), may

help show the size, living conditions, or eating habits of the organism. Trace fossils do

not include the original organism, and are often difficult to connect to a particular

species.

Naming Organisms

In science every creature is given

two formal Latin or Latinized names - one

designating the genus and the other, the

species. Species are grouped together in a

genus by shared similarities. Those

classifications most useful in evolutionary

studies also reflect evolutionary

relationships and descent from a common

ancestor. Classifications are based on the

presence of homologous features (having

the same relative position, proportion,

value, or structure due to inheritance).

Features which are merely similar are

known as analogous, resulting from

convergent evolution. Analogous features

may be similar due to similar function or

ecological adaptations, not from a common

ancestor. Symmetry type is one of the

more useful characteristics in grouping

organisms, so be sure to note the symmetry

as well as other distinguishing features of

the study samples. We will only be as

specific as the class name for most of the

fossils we study.

All of the earliest organisms were marine (salt-water) dwelling. Non-marine

organisms are ones that live in freshwater or on land. In the Animal Kingdom, the only phyla

to make the transition from marine to non-marine were Mollusca, Arthropoda, and Chordata.

The table on the next page outlines some of the major changes in non-marine life through

geologic time.

Fossil Age Ranges

The following is a list of major

fossils groups and their age ranges (when

the organism evolved, followed by the

geologic time period that the organism

went extinct). Note that geologic ages

represent when each group formed a

noticeable part of the fossil record.