Geology 105 - Paleontology
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Lab #3: Sponges and Corals

At the end of this lab, you should be able to:

  1. 1. Identify a fossil as a sponge, archeocyathid, rugose, tabulate or scleractinian coral.
  2. 2. Know the skeletal structure and material of each of these animals.
  3. 3. Know the ecological characteristics of each of these animals.
  4. 4. Know the geologic range of each of these groups.
  5. 5. Know a few important genera (mentioned by name in this handout) for each group.

Display

Look carefully at the display specimens. Use your Critter Chart and textbook to help you find the important morphological features of each group.

Sponges (#90, 507, 506, 1622): pores, spicules, internal cavity (spongocoel), osculum

Archeocyathids (#674): cone-in-cone construction, septa, osculum, pores

Corals -

Questions:

Answer these questions about specific specimens:

Sponges
1. Specimen #156. Hydnoceras was an important reef builder in the latest Devonian. Does it show evidence of a well-organized skeleton? Look at the pattern of spicules. Is this a siliceous (Hexactinellida) or calcareous (Calcarea) sponge?



2. Specimen#142. Astreospongia is an important index fossil for the Silurian and Devonian. Find and sketch a spicule. Does this sponge show evidence of a well-organized skeleton? Is this a siliceous or calcareous sponge?



3. Specimen #505. Look at the cross-section through this sponge. Trace the path water would take through this animal. What is the mode of preservation for this fossil?


4. Specimen #358. Look carefully at the surface structure and the cross-section of this sponge. Do you see the external structure reflected in the internal structure? What kind of preservation is this? (You might want to compare this sample to #505).



5. Specimen #166. Examine this small spherical sponge carefully. How could you tell this is not just a pebble?



6. Specimen #23. This is a very early sponge fossil. Find spicules in this sample. How are they preserved? From the shape of the spicules, do you think this is more likely to be a silica or calcareous sponge?



Stromatoporoid
7. Stromatoporoids were very important reef builders of the Silurian and Devonian, but are otherwise mysterious. Paleontologists have described them as everything from cyanobacteria to their own extinct phylum, but their closest affinities seem to be with a small group of encrusting sponges, the Sclerospongea (not a name you need to remember). Contrast this stromatoporoid (#1614) with the stromatolite (#162). Stromatolites are fossils of algae, where sediment accumulated on the sticky bodies of single-celled algae forming thin layers. What are the morphologic features that let you distinguish the stromatoporoid form the stromatolite? Is #154 a stromatoporoid or stromatolite? What is your evidence?

 



Archeocyathid
8. Specimen #1613. Orient this sample as the organism would have been in life. How did water move through this specimen? Why are archeocyathids though to be closely related to sponges?

 



Corals
9. Specimen #839 is a mass of gregarious rugose corals which have grown up next to each other. (Gregarious means the organisms live in groups without being truly colonial - without being connected by soft tissue. Human beings, dogs, prairie dogs, lions are all gregarious animals).
Specimen # 657is the tabulate coral Favosites, a truly colonial coral.
Is specimen #521 a rugose or tabulate coral? To answer this question, think about what structural features distinguish the two groups. Do you think this organism was gregarious or colonial (a tricky question when no soft tissue remains)? Cite your evidence for both questions.

 



10. Specimen #1698, unlabelled specimen. One of these is a solitary rugose coral (Zaphrentis); the other is a solitary scleractinian. Which is which? Cite your evidence.

 



11. Specimen 516. Look carefully at the internal structure of this rugose coral . What are the lines running across the organism? How did these structures change over the lifetime of the organism?

 



12. Specimen 1417/1418. This sample contains 2 corals. What group does each belong to?



13. Specimen #829. Does this sample represent catastrophic burial of a living community, or an accumuloation of dead material? What is your evidence?

 



14. Specimen # 482. This is a colonial scleractinian coral. In life, where would the polyps be located? What skeletal material is this? What is the mode of preservation?



15. Specimen #888. This is a colonial rugose coral. Do you think this coral had zooxanthellae? Why or why not?



16. Specimen #1678. How is this fossil preserved?