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Class Notes: Bioarchaeology

Wednesday: November 2, 2011

Week 9: Diet II & Chemistry (Stable Isotopes and Trace Elements)

Tuesday:

Teeth are the only hard tissues in the body that directly interact with the environment. As such, they are of great use for bioarchaeological research. Dental macrowear is scored commonly on Scott’s ordinal scale. Teeth wear over time, and in ancient populations the wear was so great that almost nothing of the tooth would be left, and indeed sometimes the body would purge the tooth altogether. Macrowear studies this pattern, which can have different sequencing depending on diet and subsistence.

Dental topography was developed within the last decade, applying geological mountain mapping software to dental crowns.  This turns what is visually seen in Scott’s scale to quantitative data. [At school, it is part of my job as the research associate to use the 3D plotter machine to profile each tooth from Dr. S’s project to create a virtual catalogue.]

Dental microwear studies a tooth’s microscopic texture, including pitting and scratching. A scanning electron microscope (SEM) is a common method in doing so. Teeth are coated with a very fine layer of metal, then an electron gun shoots the specimen inside a vacuum chamber. The electrons will bounce off the object and the software is able to transform a 3D object into a 2D representation using a horizontal scan. Newer technology does exist to create a 3D model, but this is not yet typical.

A 3D method that is gaining speed, however, is that of the while light confocal microscopy profiler (WLCP). [The major part of my duties in the department.] It is similar to a compound microscope, except a beam of light is shot through the lens and bounces back. This distance is measured to created a vertical scan of the specimen. It uses scale sensitive fractal geometry to calculate variables like complexity of the occlusal surface, anisotropy and heterogeneity of features, and texture fill volume.

As usual, we discussed several case studies to wrap class up.

Thursday:

Class was almost entirely discussion from the texts. I admit that I still need to read these chapters, so this bit may not be the clearest. Stable isotopes and trace elements can provide evidence for the type of diet an individual ate. We discussed measuring carbon, nitrogen, and oxygen with a mass spectrometer. This breaks a sample down to its elemental parts, weighing each element separately. For instance, when measured, the delta of  13C can indicate a marine versus a terrestrial diet. Marine foods will show a delta closer to zero, while terrestrial foods will be closer to -7. Another benefit is that plants discriminate differentially to 13C in their photosynthesis, so C3 plants can be differentiated from C4 plants in the archaeological record. The benefit here is that maize is a C4 plant so the adoption of maize can be noted in archaeological remains. Nitrogen likewise proves a valuable factor of understanding diet, giving a trophic accumulation of 15N. Legumes will provide a base level of 15N, herbivores who eat these legumes will have a slightly higher value, and carnivores who eat the herbivores who eat the legumes will likewise have an even higher value. 15N therefore needs to be understood within the environmental context, because comparisons between environments like coastal versus inland, or arid versus humid will give the incorrect impressions. Oxygen analysis of both bone and teeth (18O), as well as strontium, can show migration patterns because it is linked to the available water source.

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2 remarks!

  1. I am having a problem with pronouncing the words – let alone trying to remember them . etc.

  2. Haha, sometimes when I am taking notes, I ask myself “why did I pick a field with so many big words?”

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