Name __________________________________
Period __________
Date ____________________________
Symmetry
One of the distinctive features of living and fossil organisms, particularly animals and higher plants, is their symmetry
and proportion. If one examines a living organism or a fossil, it can be seen that they are usually designed with a
symmetrical shape which can be divided into two or more equal segments or parts. The fundamental patterns of
symmetrical form and shape are radial, pentagonal (a type of radial), and bilateral. Some organisms build skeletons
which become asymmetrical.
Procedure
Categorize each fossil in the set by its symmetry. Sketch a picture of the fossil and write its name in the appropriate
column below.
Bilateral
Radial
Pentagonal
Asymmetrical
Coiling
Many fossil organisms have shells that are coiled. The type and direction of coiling is frequently a guide to identifying
the shell. If the organism is coiled on an axis which is in a plane, it is termed planispiral. If the axis of coiling is on a
spiral, it is termed trochosprial. Another basis of coiling is whether or not the shell coils up like a hose (evolute), or
whether the shell expands in width as it grows and in effect “swallows” the first or earlier parts of the shell into later
ones (involute).
Procedure
First, remove all of the coiled fossils from the set. Write their names in the appropriate column in the chart below.
Planispiral/Evolute
Planispiral/Involute
Trochospiral/Evolute
Trochospiral/Involute
Chronological Arrangement
The study of fossils helps us to determine many things about the Earth's past including: (1) the geographic range of fossil
species over the Earth; (2) the extent of a species or a group of organisms in time; (3) the types of organisms that lived in
communities in various environments; and (4) the changes in the form and nature of organisms through time.
Procedure
Using the "Fossil Guide" and the "Fossils and Time Chart", arrange the model fossils within the appropriate division of
geologic time. Then, answer the questions that follow using the "Taxonomy Chart".
1. You will note that the Paleozoic fossils as a group are different from the Mesozoic and Cenozoic assemblages. What
differences do you see?
2. As a group how does the Cenozoic assemblage differ from that of the Mesozoic and Paleozoic?
3. Describe any evidence of change through geologic time you see in any closely related groups of organisms.
Pull out all of the organisms from the Phylum Mollusca and put them in chronological order.
4. What similarities do you observe between these organisms? Differences?
5. How have these organisms appeared to change over geologic time?
6. Why are so few organisms preserved as fossils?
7. Differentiate between a chemically altered (petrified) fossil and a cast fossil.