Lesson 4 - Page 4



MATERIALS: PAST LIFE: FOSSILS, Swift GH microscope or Hand Lens 

PROBLEM: How can you tell what kind of organism a fossil represents?


PROCEDURE: Examine each fossil specimen and answer the questions about them. When you have finished, complete the fossil description chart (Question 10)


Trilobites were three lobed animals related to arthropods. They were marine organisms that ate debris that had accumulated on the bottom of the sea. They were a type of deposit feeder. Trilobites ranged in length from a few millimeters to almost 20 centimeters. Trilobites lived during the Paleozoic Era, between 545-220 million years ago.

A. What type of environment did trilobites live in? Because these organisms are now extinct, how can we tell what they looked like?

B. What living organism from the previous lab do trilobites resemble?

C. Sketch your trilobite.




Ammonites lived during the late Paleozoic and Mesozoic Eras (395-65 million years ago), but are now extinct. Ammonites were a type of mollusk, belonging to the class of Cephalopods. Cephalopods are best known for their arms and tentacles. An octopus is a modern example of a cephalopod. Ammonites probably had eight to ten tentacles which they used to move about and to catch food. Your specimen is only the shell of the ammonite. The ammonite lived in the larger opening at the end of the shell. The shell acts as protection and enabled the ammonite to regulate its body pressure as it moved through different depths of water.

A. This ammonite specimen came from Morocco. Where is Morocco? Can you predict the type of environment in Morocco area when this organism was alive?

B. What organisms does this resemble from the previous lab? Why?

C. Sketch the ammonite.



3. ORTHOCERAS (Nautiloid)

Like ammonites, Nautiloids  are a type of extinct cephalopod within the Mollusk group. Orthoceras is the genus name of a particular group of a nautiloid cephalopod.  The shell of the ammonite has a spiral shape, whereas the shell of Orthoceras is elongated. If you look closely at your specimen, you may be able to see the chambers within the shell where the organism lived.

A. Compare Orthoceras with the sea urchin spine that you observed in the previous lab on present day organisms. How are they similar? How are they different? Could you mistakenly believe these fossils are from related organisms? Why?

B. Sketch your Orthoceras.




This shark tooth is between 10 and 25 million years in age. The specimens are from Morocco. Every time a shark takes a bite, they eat their own teeth and whatever they bit into. Whey the shark "poops" the teeth are removed from the sharks systems and becomes a fossil.

A. Compare these specimens with the shark jaw that you saw in the previous lab. What are the differences and similarities? How big do you think this shark was?

B. Sketch your specimen.




Crinoids belong to the phylum Echinodermata, which includes sea stars and sand dollars. Crinoids were diverse in the Paleozoic. They attached to the marine floor using a tree-like stem. The organism’s main body which has arms radiating from its body, is attached on the top.

A. Compare the crinoid stem with the sea urchin spine. How are the two specimens similar, and how are they different? Could you mistakenly believe these fossils are from related organisms? Why or why not?

B. Sketch the crinoid stem.



6. GASTROPOD (Turritella agate)

Gastropods belong to the Phylum Mollusca. Their shells have a spiral symmetry, which makes them easy to recognize. In your specimen, the original shell material has been replaced by quartz (agate).

A. How do you know that these are fossil gastropods?

B. Why is the specimen shiny?

C. Sketch as many different gastropods as you can find in your specimen.



D. To which living organisms from the previous lab are these fossils most related? Explain.


Brachiopods were abundant animals in the seas of the Paleozoic Era. Starting about 200 million years ago, the Mollusk group took over their living spaces. Today, brachiopods only live in deep marine water, and are not abundant.

A. On the surface a brachiopod looks like a "clam." However, there is something different about the shells. What is the difference?

B. Sketch the brachiopod.




C. Which living organisms from the previous lab are these fossils most related? Explain


When fish die, their remains can settle to the ocean floor. If there is rapid burial, the fish will compress over time and a chemical change will convert the fish’s organic body into a film of carbon that is like an outline of the living fish.

A. Make a sketch of the specimen. Make a second sketch of what you think it may have looked like when this fish was alive.



B. Why is the specimen brown?


Sea urchins belong to the Echinodermata and has a typical five part symmetry. The spines help the sea urchin move and help protect the living organism.

A. Sketch the sea urchin spine. Point out which end was attached to the body of the sea urchin.



B. Does this specimen look similar to the sea urchin spine in the previous lab?

C. Could you guess what organism this belongs to if you didn’t have a knowledge of the present? Explain.

D. What other inanimate or animate object could you confuse this with? (Use your imagination.)

10. Using your answers from questions 1 to 9, complete the chart below.








shark tooth (Morocco)








(Nevada or Wyoming)


crinoid stem


sea urchin spine



[Back to Past Life]  [Back to Earth Science Grid]