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.