Paleontology

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Paleontology
The study of ancient life.
In this Power Point Lab you will see how
geologists, particularly paleontologists, use
fossils to learn more about the past. ()
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This lab will concentrate on three aspects of
fossils
1. The methods of fossil preservation.
2. The use of fossils to determine the
environment of deposition of the sediment in
which they are found.
3. The identification of a few major types of
invertebrate fossils.
FOSSIL The trace of any living organism that
was preserved naturally in the rock record and is
at least 6000 years old (prehistoric). ()
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Fossil Preservation
The method and completeness of fossilization
determines how much information can be extracted
from the fossil. Preservation can be complete
with the original material preserved. An example
would be a wooly mammoth trapped in Arctic ice.
This provides a tremendous amount of information,
even DNA is preserved.
OR, fossilization could be only a foot print or a
burrow left by an animal which has only limited
value to the paleontologist. ()
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Fossil Preservation
Aside from the very unusual preservation of the
wooly mammoth in glacial ice (which is very
rare), most fossil preservation is in 3 distinct
methods. ()
REPLACEMENT
CARBON FILM
CAST OR MOLD
Lets take a look at some examples of each of
these. ()
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Replacement
Replacement refers to the removal of the original
remains of an organism and the substitution of
that matter with mineral deposits. Other than
the preservation of the original parts of the
organism (like the wooly mammoth, or
mummification), preservation by replacement is
the next best means of maintaining information
about the organism. ()
With replacement, very often the internal
structure of shells, bones, teeth or claws and
even wood are preserved. ()
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Replacement
These are examples of internal structures. The
sponge fossil on the left has preserved the
various canals in which the sponge circulates the
water to filter nutrients. On the right the
stromatolite displays the layer upon layer of its
growth. The stromatolite is a blue green algae
that lived in the ocean over 2 billion years ago.
()
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Carbon Film
As the name implies, a carbon film is flat and
black. Carbon films are produced when an
organism, normally without any hard parts, is
buried and compressed. This compaction drives
off the volatiles and leaves behind a carbon
(black) residue. Although there are many
examples of carbon films in the fossil record
including worms, fish, and tree limbs, the most
abundant fossil type is leaves. ()
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Carbon Film
Note that the rock in which the fossil is found
is fine grained shale. This is a low energy
environment that does not have turbulence that
would destroy delicate fossils. ()
The environment of deposition for this sample
would be a swamp or lake. ()
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Carbon Film
This is definitely a carbon film, just a flat,
black spot on this piece of shale. The organism
that left this mark was a brachiopod. ()
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Molds and Casts
Casts and molds are normally discussed together
although they are not quite the same thing. For
example, if a dinosaur steps into some soft sand
and leaves a footprint, that is an example of a
mold. If that footprint is then filled in with
sand and it becomes lithified, that sandstone is
the cast. The cast is the filling and the mold
is the impression (or indentation). (I do want
you to distinguish between a cast and a
mold.) Here are some examples. ()
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Molds and Casts
The plaster becomes the CAST. In nature, of
course, the impression of a plant or animal would
be filled with silt, clay, sand or some other
natural substance. This filling would become the
cast. ()
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Trace Fossils
A trace fossil is nothing more than a clue as to
what the organism was. For example, footprints
give paleontologists some insight on the weight
of the animal and its size. The structure of the
print can also be used to determine the use of
the foot does it have claws, pads, long toes,
short toes or toes at all. Sometimes a walkway
is recovered from the rocks. This can reveal
clues about the animals gait or how big it was
and how fast it was moving. Other trace fossils
include burrows, coprolites, gastroliths, skin
impressions, or even something as trivial as a
leaf blowing across a sand dune leaving a trail
of its adventure. Here are some examples. ()
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Trace Fossils
These are tracks left by some bottom feeding
animal, maybe a snail. This is probably a record
of a grazing pattern. ()
This is a coprolite. It is preserved excrement,
in this case from a fox like animal. Coporolites
provide valuable clues to the diet of the animals
that produced them. ()
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Practice Quiz
Here are some samples of various types of
fossils. When the image appears, study it and
look for clues of the method of fossilization.
When you have made your decision, advance to the
answer. Remember your choices are limited to
these five choices REPLACEMENT, CAST, MOLD,
CARBON FILM or TRACE FOSSIL()
This is an example of replacement. This is a
section of a tree trunk from Petrified Forest
National Park, AZ. Notice that in the large
trunk there are some tree rings that have been
preserved. These are internal structures that
indicate replacement. ()
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Practice Quiz
You are looking at a fossil that has been cut in
half.
()
This is an example of replacement. This is a
fossil nautiloid. Nautiloids were squid like
marine animals that produced a shell. As the
animal grew it added chambers that accommodated
its larger size and it could regulate its
buoyancy by pushing gas in or out of the
chambers. This specimen has been sawed in half
with a diamond saw to show this internal
structure. ()
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Practice Quiz
()
This is an other example of replacement. In fact
it is another squid like animal called an
ammonite. Here a portion of its outer shell has
been worn away to show the intricate structure of
its chamber walls. ()
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Practice Quiz
()
This is an example of a carbon film. These leaf
fossils accumulated in a swampy area and were
then buried by more sediments. The result was
that compaction pressures flattened the leaves
and drove off all of the material making up the
leaf except the carbon. ()
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Practice Quiz
()
This is an example of a cast. This is a plaster
cast of a trilobite. If this were broken, it
obviously would not have any internal structure.
()
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Practice Quiz
Identify the light, branching lines.
()
This one is a bit more difficult and I would not
have expected you to correctly identify it. This
is a clam shell from Rocky Point. The shell has
a bright light bulb behind it and showing through
the shell are lighter markings. These were
produced by a boring sponge. The sponge bored
into the shell for protection from the pounding
waves. This is an example of a TRACE FOSSIL.
()
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ENVIRONMENT OF DEPOSITION
Many organisms are very particular about where
they live their ecological niche. For example
fish like water. It would be not be likely that
you would find a fish in a sand dune environment.
Similarly, you would not expect to find a
tarantula fossil in a marine limestone. ()
The point is that certain plants and animals are
indicators of to the environment in which they
are living. Some are obvious like fish.
Paleontologists make it their business to learn
about living organisms so that they can better
understand life of the past. ()
In fact, the expression The present is the key
to the past. is especially appropriate to
paleontology. We know that pine trees today are
terrestrial (they lived on land). So if we find
the remains of a pine tree in sandstone, we
assume it was a terrestrial sediment. We know
that corals are marine (normal salt water)
organisms. If we find fossil corals we know that
the rock in which they are found were marine
deposits. This is what is meant by the
ENVIRONMENT OF DEPOSITION ()
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ENVIRONMENT OF DEPOSITION
The Brachiopods
There are many organisms that have very
particular environmental niches. This part of
the lab will concentrate on a few invertebrates
that are widely used among paleontologists. The
reason for focusing on invertebrates is that they
are by far the most commonly preserved in the
rock record. ()
Brachiopoda is a phylum of shelled invertebrate
that is still around today. They are exclusively
marine animals, i.e., they lived in salt water.
They lived in shallow to deep waters that were
cold or warm, silt laden or clean. So, as a
group, they simply indicate marine conditions.
Here are some examples. ()
()
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ENVIRONMENT OF DEPOSITION
The Brachiopods
The brachiopod on the left has been replaced with
pyrite and the one on the right has been replaced
with quartz with hematite (red color). The
reason that we know that these brachiopods did
not develop these shell minerals naturally is
that brachiopods today do not. The present is
the key to the past. ()
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ENVIRONMENT OF DEPOSITION
The Brachiopods
There are thousands of fossil species of
brachiopods. The fossil below is of just one
shell. This well preserved (replacement)
specimen shows the mechanism of attachment of the
shells. It had hinged teeth for opening and
closing (as shown by the green arrows. ()
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ENVIRONMENT OF DEPOSITION
Crinoids
Crinoids were also called sea lilies in
allusion to their shape. They are actually
animals related to starfish and sea urchins but
they had a long slender stalk
that supported their main body called the calyx.
On the other end the stalk was modified into
sections that held the animal in place on the
ocean floor. These were like roots. ()
Crinoids were filter feeders and lived in
shallow, warm, clean marine waters. So when we
find crinoid fossils today, we assume this was
the environment of their accumulation
(deposition). ()
Crinoid Calyx
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ENVIRONMENT OF DEPOSITION
Crinoids
Here is another crinoid calyx from Indiana from a
time long ago when this area was below a shallow,
warm, clean ocean. ()
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ENVIRONMENT OF DEPOSITION
Crinoids
This is another crinoid calyx. It show its many
arms, some of which have many fine tendrils that
were used in filtering sea water for nutrients.
()
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ENVIRONMENT OF DEPOSITION
Crinoids
This is a crinoidal limestone from Indiana. Each
of the discs is a section of a crinoid. When the
animal died the discs usually fell apart. Here
they were gathered by weak currents to produce
this limestone dominated by crinoid fragments. ()
This portion of a crinoid stem show some of the
internal structure of this part of the animal.
The fact that some internal structure is
preserved in an indication that this is
fossilization by replacement. ()
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ENVIRONMENT OF DEPOSITION
Trilobites
Trilobites were some of the most successful
invertebrates that lived in the ancient oceans.
They were all marine organisms that are now
extinct. Finding a trilobite in a rock tells a
paleontologist that the rock is at least 225
million to 575 million years old. ()
In addition to fact that they are used to
determine the environment of deposition,
trilobites were so varied and distinct that they
are used as INDEX FOSSILS, i.e., that are used to
tell the age of the rock in which they are
found. Here are some more examples of trilobites.
()
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ENVIRONMENT OF DEPOSITION
Trilobites
This may be one of the best known trilobites. It
is called Elrathia kingii. It is from the
Wheeler Shale Formation of central Utah. Finding
this fossil in the shale indicates that the shale
is around 550 million years old. The little
agnostid trilobite seen below is another species
found in the shale. ()
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ENVIRONMENT OF DEPOSITION
Trilobites
The intricate spines on this trilobite was
probably an adaptation for protection. It would
have made it difficult for a predator to kill and
swallow this critter. ()
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ENVIRONMENT OF DEPOSITION
Trilobites
This trilobite had an enlarged glabella (central
nervous system). It also had well developed
faceted eyes. Faceted eyes are like those on
flies, dragon flies and butterflies. ()
Glabella
Lets take a look at a few more trilobites. By
the way the name trilobite refers to the three
lobes. The central lobe (where the word Eyes
is located and a lobe on either side. ()
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ENVIRONMENT OF DEPOSITION
Trilobites
The trilobites are a fossil type I want you to
know. ()
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ENVIRONMENT OF DEPOSITION
There are other clues to the environment of
deposition. ()
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ENVIRONMENT OF DEPOSITION
This is coquina. This is a representation of a
beach environment. ()
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ENVIRONMENT OF DEPOSITION
This is cross bedding. It is an indication of a
dune environment. ()
This sandstone is in Zion National Park in
southern Utah. It is a formation that was formed
when this part of the world was a vast desert.
()
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ENVIRONMENT OF DEPOSITION
These are gypsum veins in a reddish siltstone.
Gypsum is an indication of aridity. These
sediments were in an terrestrial environment that
was subject to extensive drying. ()
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ENVIRONMENT OF DEPOSITION
Here is a photograph of Scientist Cliffs in
Maryland. What do you think was the environment
of deposition ? ()
This is a beach deposit. ()
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ENVIRONMENT OF DEPOSITION
Here is a photograph taken in Oak Creek Canyon,
AZ. What do you think was the environment of
deposition ? ()
This is a dune deposit. ()
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REVIEW
After this lab you should be able to
Describe and identify the various methods of
fossilization including Replacement Casts Molds
Carbon Films Trace Fossils
Identify various type of depositional
environments by using fossils.
Identify brachiopods, trilobites and nautiloids
fossils from pictures. ()
THE END