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(8) Earth in space and time. The student knows
that fossils provide evidence for geological and
biological evolution. Students are expected to:
(a) analyze and evaluate a variety of fossil types such as
transitional fossils, proposed transitional fossils, fossil
lineages, and significant fossil deposits with regard to their
appearance, completeness, and alignment with scientific
explanations in light of this fossil data;
(b) explain how sedimentation, fossilization, and speciation
affect the degree of completeness of the fossil record
(c) evaluate the significance of the terminal Permian and
Cretaceous mass extinction events, including adaptive
radiations of organisms after the events.
Fossilization refers to the series of changes that occurs to an
organism after death, that leads to replacement of minerals in
the original hard parts (shells, skeletons, teeth, horns, scales)
with different minerals.
• a process known as remineralization.
In addition, the term "fossil" is
applied in other ways, for example,
to preserved soils and landscapes
such as fossil dunes.
Through the study of fossils, it is
possible to reconstruct ancient
communities of living organisms and
to trace the evolution of species.
Fossils are usually formed when an organism is covered
by sediments (sedimentation) that then harden into
sandstone, slate, mudstone or flint (lithification).
Most organisms do not fossilize and those that do
are usually destroyed by geological processes or they
never surface for examination. Fossils that formed here, are
dragged beneath the crust
and destroyed in the
body construction: Does the organism have hard or soft
body parts?
• environment: Do the surrounding conditions allow for rapid
burial and preservation? Will the body be exposed to many
elements of erosion?
• presence of predators: Are other organisms going to
destroy the body before it can be preserved?
• If an individual is successfully fossilized and enters the
lithosphere, ongoing tectonic activity may stretch or melt it
in metamorphic processes in Earth's interior, or be weathered
away at Earth's surface.
• A fossil that has survived or avoided these events may
even succumb to improper collection techniques at the hands
of a human. All of these events and occurrences make the
fossil record, at best, incomplete
1. When the original hard parts of organisms become
replaced by different minerals, the process of _____
has occurred.
2. Because we study fossils we are able to do what two
3. What is the process whereby organisms are covered
with sediment?
4. What process forms sandstone, shale, and slate, or
5. What five things affect the completeness of the fossil
An exception is the Burgess Shale, in British
Columbia, where a number of soft-bodied
creatures were fossilized under highly favorable
conditions. These creatures have few relatives
that have been recorded in the fossil record; this
is due to the unlikelihood of the soft animals
being fossilized.
The Burgess Shale was discovered by
paleontologist Charles Walcott in 1909, towards
the end of the season's fieldwork
Badlands is a term used to denote what are usually areas that are
extensively eroded by wind and water, with many canyons,
ravines, and gullies, and other complex geological formations.
There are many “badlands” in the United States, in Utah,
Montana, Colorado…North and South Dakota. All of them are
fossil havens, rich in paleontological treasures.
The fossils of the Badlands are important because they represent
a well-preserved window into the past. They not only tell us what
lived here, but also what the environment was like at the time.
From fossils we can learn about food webs and food chains during
ancient times and how they compare to today.
Fossils are the remains or traces of an organism, or
environment, from Earth’s prehistory.
Biologists generally recognize two types of fossils.
the actual body or body parts
Zooliths and Phyto-fossils of an organism, whether
altered or not…sometimes
referred to as “body fossils”
any evidence of past life that is not
• Ichnofossils a body fossil. Examples include
footprints, trails, burrows, borings,
impressions, molds, casts, and
coprolites…usually referred to as
“trace fossils”
Geologists also recognize fossilized environments, such
as sand dunes, as said earlier.
6. Where is a famous fossil site for soft-bodied
organisms found?
7. Who discovered the Burgess Shale?
8. What two types of fossils do paleontologists
generally recognize?
9. What is the difference between a zoolith and a
10. What is another name for “trace fossil”?
• Unaltered remains This category includes those fossils that have
Unaltered skeletal
material, tar
impregnation, amber
undergone little or no change in structure and
As a general rule an organism which lived fairly
recently has a greater probability of being
unaltered than a more ancient one.
As the sediments that entomb fossils
• Altered Remains become compressed by the weight of
overlying sediments, they slowly
become rocks. The same processes
dissolution/replacement, that turn sediments into rocks can alter
organic remains .
Silica and Pyrite
11. Of the body fossils, describe ONE of the
processes that create unaltered remains…
altered remains…
A fossil is any trace of past life. A fossil does not have to be an
actual piece of an ancient organism. Many fossils are bones,
shells, or other body parts. However footprints and other traces
are fossils too.
Any reproduction of the anatomical features of the
internal or external surface of an organism. Animal
• Mold tracks preserved in rocks may be termed external
molds. Internal molds, particularly of shells, are
sometimes called Steinkerns. An impression is actually
and external mold.
• Cast
This is, in general, a duplication of the original. Casts
are formed when original parts are dissolved away and
the resulting space becomes filled either with sediment
or mineral matter, which harden to form rock.
It is very difficult to distinguish a cast from an
altered body fossil, such as permineralization.
• Borings and Burrows
Certain worms and clams and
many other invertebrates burrow
into rocks, wood, shells, and all
types of sediment. These burrows
are frequently preserved,
especially in fine-grained rocks.
• Copralites
Fossil excrement can sometimes give definitive
knowledge about the diet and size of the animal
When you know what the organism ate, you
know a little more about the environment too.
These are smooth, polished stones that are often
found in the abdominal cavities of the skeletons
Gastroliths of dinosaurs. They are thought to have helped
those huge animals grind up vegetable matter in
their stomachs or gizzards just as in chickens of
If it weren’t for their association with skeletal fossils,
gastroliths would look like any polished river rocks.
Rodents and other animals chew on plants for
nourishment and on bones for the calcium content
and did so in the past. Gnawed plants and bones
are frequently preserved as fossils.
12. Describe and give examples of the following
• Mold
• Cast
• Coprolites
• Gastroliths
13. What kinds of things can a paleontologist
learn from studying coprolites?
Fossils are found on every continent and even on the sea floors.
By far, most of them are invertebrates with hard parts (for
example, mussels).
Vertebrates, the class that includes fish, amphibians, reptiles,
birds and mammals, are a relatively late development, and the
finding of a large, complete vertebrate fossil, with all its parts
close together, is rare.
Microfossils, on the other hand, are extremely common. The
microfossils include very early bacteria and algae (stromatolites);
the unicellular organisms called foraminiferans, which were
common in the Tertiary Periods; and fossil pollen. The study of
micro fossils is a specialized field called micropaleontology.
• is any fossilized remains of a
life form that exhibit
characteristics of two
taxonomic groups.
• is the fossil of an organism
near the branching point where
major individual lineages
• will have characteristics
typical of organisms on both
sides of the split.
The principal use of fossils by geologists has been to date rock
layers that have been deposited over millions of years, and as a
guide to evolutionary processes. Evolutionary succession can
easily be seen in the fossil record.
Distinctive fossilized life forms that are
typically associated with given intervals
of geologic time are known as index
fossils, or indicator species.
The concepts that different fossil
species correlate with different strata
and that, in the absence of upheaval,
older strata underlie younger ones are
attributed to the English geologist
William Smith, who worked in the
early nineteenth century, as well as
Nicholas Steno, to more fully develop
the Law of Superposition.
Five major mass extinctions have occurred since
life began on Earth. The rest have been
“background extinctions”, occurring throughout
While extinction events may spell doom for many
genera on Earth, they also spell “glory” for
Mammals would never have gotten a strong
foothold were it not for the extinction of the
dinosaurs, 65,000,000 years ago.
What animal group do you think will prosper and diversify when humans are
14. What is a transitional fossil, and what do they
show? Give an example.
15. What is an index fossil used for? Give and
16. Who is responsible for the development of
the Law of Superposition?
It is still somewhat of a
mystery as to what caused
the Permian Mass
extinction…if indeed it was
even one event. Many
speculate that it was a
combination of impacts,
The hardy “disaster taxa” Lystrosaurus
volcanic eruptions, and other
were the only abundant terrestrial
geologic upheavals that
vertebrates to make it through the event. caused the extinction. We do
know that there was a lower
There were no coal formations during this oxygen content and a higher
2 content during this
time period, which leads scientists to think CO
period, and that organisms
that there was not enough floral biomass to able to adapt made it
through the extinction.
produce coal.
The Permian “Great Dying” Mass extinction
was responsible for the extinction of 96%
of the marine life, and 70% of the
terrestrial life.
Without floral biomass, the herbivores like
rhynchosaurs were not supported, and thus
became extinct.
• Generalists
Resistant to extinction
• Specialists
Prone to extinction
Adaptive radiation occurs when animal and plant groups “adapt” ,
evolve, and “radiate” outward… in other words, diversify.
wereof organisms
Mass extinction events allow for adaptive
to occur. When one group of organisms isterrestrial
dominant on Earth for
too long a period of time, evolutionary processes
“slow down”.
organisms for
over 160,000,000
Mass extinctions allow for rapid bursts of speciation
to occur, and
both plants and animals flourish.
The diapsids, ("reptiles“) except for turtles and a few extinct
forms, rose to prominence during the latter Triassic times, later
giving rise to the dinosaurs.
Mass extinction is IMPORTANT to evolutionary processes.
• occurred approximately 65.5 million years ago
Several impact craters (Chicxulub) and
massive volcanic activity, such as that in
the Deccan traps, have been dated to the
approximate time of the extinction event.
The combination of these events may
have reduced sunlight and hindered
photosynthesis, also changing sea-levels,
leading to a massive disruption in Earth's
food webs.
Many researchers believe the extinction
was more gradual, perhaps taking millions
of years.
Either way, all the major extinctions were
gateways to new evolutionary events.
17. Why are mass extinctions so important to
evolutionary processes?
18. What types of factors might make organisms
resistant to extinction?