1. For this exercise you will gain an appreciation for the difference between fossils, molds, and casts. Rubber molds are created from the original fossil. Using the rubber molds and plaster of Paris, you will make a cast (or replica of the original fossil). Do this at the beginning of the lab, so that your plaster will have time to set (takes half an hour or more).

Plaster cast of fossil on left, and blue latex mold on right.

2. Examine the fossil specimens provided by your instructor. Give the type (or types) of preservation of each, as specifically as possible. If the hard parts are original material, please specify its composition. If the fossil consists of chemically altered hard parts, please specify the type of alteration that has occurred (permineralization, etc.) as well as the present composition. If you can see the imprints of hard parts in the sediment, please tell whether they are internal molds, external molds, or casts. If you are looking at a trace fossil, please specify what type.

2. Examine the photograph from Dinosaur Ridge near Morrison, Colorado, and answer the following questions.

1. Is the rock most probably of marine or non-marine origin?

   _________________________________________

2. What additional features would you look for to confirm your answer to question a, if you could examine the locality where these samples were collected?

   __________________________________________________________________

3. How many different animals left their mark on the rock?

   __________________________________________________________________

4. Are these tracks or trackways? ___________________

5. What is a possible origin of the circular imprints near the larger 3-toed tracks at the top of the image?

   ____________________________________________________

3. Examine the photograph and answer the following questions.

1. What types of behavior are suggested by the trails?

   _________________________________________________________________

2. What types of marine invertebrates may have produced these trails?

   __________________________________________________________________

3. What other sedimentary structure is present here?

   ____________________________________________________________________

4. What type of rock is this most likely to be?

   ____________________________________________________________________

5. What was the most probable depositional environment for this slab of rock?

   ____________________________________________________________________

4. The sketches below represent a cross-section of a bivalve shell with the hinge at the left. Complete the drawings below by shading in the part that would become:

Internal mold	External mold	Cast

Remember that the internal mold forms from the sediment that fills the space between the valves, and the external mold forms from the sediment surrounding the exterior of the valves. The cast forms in the area the the valves once occupied.

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This page created by Pamela J. W. Gore, Pamela.Gore@gpc.edu
Georgia Perimeter College

July 20, 1998
Modified December 24, 1998
Modified September 22, 1999
Modified June 6, 2001
Modified December 13, 2003

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