Preservation Lab April 14th

Preservation Lab


(Remaining eight questions)


1. It may seem intuitively obvious that a slimy little worm is not going to have a good fossil record. But intuition is not good enough for scientists. Explain why it probably won't fossilize using at least three lines of evidence.

Although really soft, sensitive organisms can fossilize when the conditions are just right, more often than not a slimy little worm will not preserve for several reasons based on evidence:

A. They get eaten by predators after they die.

B. They get eaten by predators while still alive. This is evident by the holes in shells, for example, created by predators attempting to eat the organism inside.

C. Sediments do not cover the dead organism in time for it to fossilize.


2. Do shelled organisms that live on top of other shelled organisms increase or reduce their chances of preservation? Explain.

Based on observation, it appears that shelled organisms clumped together would increase their chances of preservation: As mentioned in class (class lecture), shells, or filter feeders, face various directions to take in food. So when they die, it seems more likely that as sediments mold in and out of the shells it would keep the shells together as they were. On the other hand, if the shells were separated before they were preserved I think that they would more likely break apart and dissolve.


3. Why do you think most fossils of birds are from lakes?

Water, especially muddy shores, seem to be ideal conditions for organisms to fossilize. When a bird dies on the shore of a lake, for example, most likely it's wet. This allows sediments to quickly stick to the bird and build up overtime.

4. How do the processes in special preservation differ from the processes in normal preservation?

Fossilization can take place when all the necessary conditions occur. These chance events can result in different types of fossilization.

In normal preservation, organisms are typically eaten by bacteria or other predators but their vertebrae or shell remain and fossilize. Special preservation, however, occurs when the tissue of an organism can be observed in the fossil (class lecture). Such events can happen when a worm, for instance, is immediately covered by sediments upon its death. According to Wikipedia (http://en.wikipedia.org/wiki/Fossil), soft organisms can preserve in areas that are low in oxygen and its chances of decaying are low. But these results are rare and exceptional.

5. What is time-averaging?

According to the class lecture, time-averaging is a tool to measure the span of time an organism populated an area. This is based on many factors, but one way to understand this process is to look at the example of the helmet shells. Fossil remains of a particular species that dominate a specific layer in sediment rock is one possible way to determine the average time the species existed. However, there can be errors in these observations. It is important though to recognize that any fossil has some time averaging.

6. Write a caption for the figure below, explaining how it illustrates time-averaging.

Figure B seems to be representing the sequence of the shells as having existed separately, whereas Figure A shows the different shells overlapping. But I do not understand what the author means by completeness and over-completeness in the context of time-averaging.

7. Compare the magnitude of time-averaging in a varve to time-averaging along the continental shelf where most fossilization occurs.

8. What was the coolest thing you learned in this lab? Why was it cool?

Several things about this lab were cool, but was particularly intrigued by seeing actual fossils and applying what I have learned thus far about them. Further, understanding how the holes occur in shells was neat: were they signs of predation? Did they already have a hole? This was certainly a thought-provoking lab that made me realize the complexities of fossilization.