Taphonomy
For the sake of this exercise, we recognize three "taphonomic grades":
- Good (1): Well preserved shells that show growth lines and ribs in their original or near-original condition.
- Fair (2): Shells in which the surface features are somewhat worn, but the growth lines and ribs are still seen.
- Poor (3): Shells in which most of the surface features are worn away and much of the shell's external surface is smooth and polished.
Examples of these three taphonomic grades are shown in the Reference collection. Look at these shells to familiarize yourself with the three taphonomic grades. You may need to refer to this reference collection later when analyzing the two samples.
Analysis: Compare the taphonomic condition of Sample A and Sample B. Three examples of Sample A are available; three of Sample B are available. Analyze one of each in the following way:
1. For each sample, tabulate the number and proportion of shells in each of the three taphonomic grades described above and illustrated in the reference collection. You might find, for example, that in one sample 30% of the shells are in "good" condition, 30% in "fair" condition, and 40% in "poor" condition. The other sample may have different proportions.
2. Plot, on the triangular diagram provided, the location of Sample A and Sample B.
3. Describe briefly how the two samples differ with respect to their taphonomic condition.
4. Discuss briefly why the taphonomic condition of the shells in the two samples might be different.
Taphonomy
Skim Chapter I in Prothero (1998), and read the section on Exceptional Preservation. Answer the following questions:
1. Why are deposits with exceptionally well-preserved fossils important? What types of information do they provide that are usually unavailable in the fossil record?
2. The Burgess shale and the Solnhofen Limestone axe 2 of the world's most famous fossil Lagerstatten. What characteristics did these depositional environments share that produce such extraordinary fossils?
Fossil concentrations
Examine the specimens of "fossil hash" - sedimentary rocks consisting largely of skeletal fragments. Fossil-rich sediments like these are favorite collecting sites for paleontologists. These kinds of concentrations may be the result of:
- Physical processes: such as storms or currents, which winnow away sediment and concentrate the most durable skeletal elements.
- Successive aggradation : ("piling up") of live individuals in their habitats, as happens on oyster banks or coral reefs.
How might you distinguish between these modes of fossil concentration?
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