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Taphonomy

What is Taphonomy?

One approach that I focus on is called taphonomy.  This helps tell me why we find fossils where we do and what the fossis may mean about the dinosaur communities that formed the fossil assemblage. Taphonomy started out as sub-field of paleontology, but only recently has established itself as a full-fledged interdisciplinary field.  It is now used not only in paleontology, but anthropology, archeology, and forensics as well.  Taphonomy describes the transfer of organic and inorganic remains of an organism from the biosphere (living world), to the lithosphere (the geological world). These are processes that act on an organism's remains following death up until discovery. These include preferential destruction of small remains/juveniles and soft tissues, the collection of remains in riverbeds, or chemical and physical destruction. This has given us some insight into which remains are preserved over others.  To add insult to injury, the fossil record itself is incomplete.  Not all times, places, and environments are equally preserved.  Understanding how this bias effects what fossils we find is vital to reconstructing the paleoecology of extinct organisms.

 

Dissertation Project

For my dissertation, I constructed several microcosms that ran under controlled laboratory conditions for 14 months.  This experiment was set up to test the effect of:

1) Matrix (sediment) type: I created two types of "soil" for my experiment; a high flow/low organic (HF/LO) matrix of 90% sand and 10% silt by volume, similar to sandy soils or riverbeds; and a low flow/high organic (LF/HO) matrix of 20% sand, 40% silt, and 40% peat by volume, similar to moist forest soil.

2) Bone size: I am using deer (large) and rabbit (small) vertebrae to see how much of a difference bone size, surface area, etc. makes in bone decay.  Do small bones just decay faster than large bones but at the same rate, or are there qualitative differences?

3) Plant type: I am interested in whether or not plants help facilitate bone decay when buried together.  Since I am also interested in dinosaurs, I am comparing the effects of angiosperm vs. non-angiosperm plant remains on bone decay, since angiosperms did not evolve until the Cretaceous Period, near the end of the dinosaurs' reign.  Could angiosperms have had an effect on the burial environment, influencing the preservation of vertebrate remains?

Each possible combination of factors were replicated three times and, along with controls, created a total of 54 experimental microcosms (see Table 1).

Table 1

Many people ask me if I will be able to see anything related to fossilization within such a short time frame. The short answer to that is: I'm not sure.  The interesting thing about my work is that not much like it has been done before, so any results (positive or negative) are helpful.

There is a long answer to that question as well: I am not studying fossilization, but the processes that act on bone before fossilization takes place.  It is generally agreed that the actual mineral replacement associated with fossilization can take a great deal of time, perhaps 10,000 years or more (and I certainly didn't want to be in grad school that long!).  However, there is good evidence that short-term processes acting on the time scale of a decade or less are deterministic in deciding whether a bone will survive to become a fossil at all.  This includes factors such as pH, soil organic matter, and hydrology.  These factors vary with environment, meaning there may be a strong climatic component to the chances of an animal becoming part of the fossil record.  If certain climates preserve vertebrates better than others, how does that affect our perceptions of their paleoecology today?  This is a question that has yet to be addressed in vertebrate paleontology.

Continue down to see pictures of my experiment....

 

 

These microcosms are constructed out of discarded 2L plastic soda bottles, supported by a wooden frame, with nozzles and clear plastic tubing for drainage.
 
Deionized water is fed into a holding tank, where CO2 gas is injected to lower the pH to the desired range of 5.6-5.7 (the pH of rain).  This water is then fed through a system of PVC pipe to each container, where drip rate is controlled by small valves.
 
Before they could be used, all deer and rabbit bones had to be manually cleaned of flesh.  This helps simplify conditions within the containers.
 
All bones were sealed in plastic containers for CT scanning in order to measure initial bone density and condition prior to burial.  They were scanned again at the end of the experiment and compared for density loss.
 
The mass and volume of every bone was carefully recorded prior to burial. Mass loss was measured after the experiment ended.
 
All plants were also washed and weighed before they were used.  An approximately equal amount was used in all treatments.
 
Images of bones being buried with some plant material.
 
Water is collected from the drain tube of each container, then filtered using a 0.22 µm syringe filter to remove particulates and bacteria.
 

The pH of each container is also regularly monitored to keep track of changing chemical conditions resulting from treatment.

Water samples are kept in glass vials and stored in a refrigerator. Water samples were analyzed using Direct Current Plasma Argon Emission Spectroscopy (DCP-AES) for calcium concentrations.The concentration of Ca in the sediment itself was measured with XRF.

 

 

 


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This page last updated June 18, 2012