Hello again, everyone. This week was mostly devoted to something only technically related to fossil faces: learning how to use ImageJ.
Last week I mentioned that the measurements I plan to take with the various A. afarensis mandibles will be digital, to ensure accuracy, and that some of the mandibles may need to be partially reconstructed. In order to do that, Dr Kimbel recommended an open-source program called ImageJ. I had hoped that, having some ancillary experience with GIMP and Photoshop, ImageJ would come easily to me, and require minimal learning time. I was wrong.
Therefore, I spent most of my time this week fiddling with ImageJ, trying to learn how to use the mirroring function effectively, among other things. I think, by this point, with as much practice as I put in, I should be fine.
The next step, then, is to actually reconstruct and measure the mandibles.
Sunday, March 8, 2015
Sunday, March 1, 2015
Week One
Hello everyone. This week, with me back in Arizona from Ohio and my on-site mentor back from Ethiopia, I could finally begin my project in earnest. And believe me, I had plenty on my plate this week; broadly, we began to find ways to build evidence for whether or not H. habilis and H. rudolfensis represent the same early-Homo species.
We began a little obliquely. One way to determine if a sample set should be classified into multiple separate groups, rather than one broad one, is to measure diversity in the sample. If, say, there is more diversity in a set of specimens than would be expected from an established species, it probably stands to reason that that set of specimens does not represent only one species. In order to form a basis for doing that, we decided to examine the mandibles of our H. habilis and H. rudolfensis specimens. Comparatively, we have a very small number of such specimens -- but we can solve this problem by comparing their degree of diversity to a well-established species with a large sample set. The obvious choice is Australopithecus afarensis, for which we have at least 17 usable (or mostly so) mandibles.
The basis for our comparison is simple. We plan to measure the mandibles of the A. afarensis specimens based on two criteria: depth of the anterior dental arcade as defined ahead of P3, and degree of divergence of the limbs of the mandible. With these measurements, we plan to construct an index of diversity to which we can compare the mandibles of the early-Homo specimens. In order to correct for size differences across specimens, both measurements are taken as relative to other features of the mandible itself; in the latter case, for example, the distance between any two complimentary pairs of molars is expressed as a percentage of the total "jaw length" (defined as the length as measured from the lingual ridge of the midline to an imaginary line immediately behind the M3s).
So, I spent quite a bit of time getting acquainted with A. afarensis jaws -- one of which was Lucy's. Once I determined, from the various specimens collected, which were usable (I ruled that there was one that could be used with extensive digital reconstruction techniques, while the rest (17 others) would be easy to prepare), I took the nine specimens that, by plaster reconstruction or preservation, were fully complete (both limbs of the mandible intact, all or most teeth still remaining) and examined them visually, attempting to evaluate their position on a continuum from most-arched to least-arched (in the anterior dental arcade), and most-divergent to least-divergent (in the limbs of the mandible); this process is mostly for initial convenience, and will be corrected (or not) by concrete empirical measurement.
What comes next week, then, is beginning to take the measurements. All of the measurements will be taken digitally to ensure as much accuracy as possible, especially on reconstructions. Therefore, measurement requires photography on a standard mandible orientation. At this point, it looks like we might be using Photoshop and Image J for our purposes in two dimensions -- if we upgrade to three, we will have to use a digitiser.
We began a little obliquely. One way to determine if a sample set should be classified into multiple separate groups, rather than one broad one, is to measure diversity in the sample. If, say, there is more diversity in a set of specimens than would be expected from an established species, it probably stands to reason that that set of specimens does not represent only one species. In order to form a basis for doing that, we decided to examine the mandibles of our H. habilis and H. rudolfensis specimens. Comparatively, we have a very small number of such specimens -- but we can solve this problem by comparing their degree of diversity to a well-established species with a large sample set. The obvious choice is Australopithecus afarensis, for which we have at least 17 usable (or mostly so) mandibles.
The basis for our comparison is simple. We plan to measure the mandibles of the A. afarensis specimens based on two criteria: depth of the anterior dental arcade as defined ahead of P3, and degree of divergence of the limbs of the mandible. With these measurements, we plan to construct an index of diversity to which we can compare the mandibles of the early-Homo specimens. In order to correct for size differences across specimens, both measurements are taken as relative to other features of the mandible itself; in the latter case, for example, the distance between any two complimentary pairs of molars is expressed as a percentage of the total "jaw length" (defined as the length as measured from the lingual ridge of the midline to an imaginary line immediately behind the M3s).
So, I spent quite a bit of time getting acquainted with A. afarensis jaws -- one of which was Lucy's. Once I determined, from the various specimens collected, which were usable (I ruled that there was one that could be used with extensive digital reconstruction techniques, while the rest (17 others) would be easy to prepare), I took the nine specimens that, by plaster reconstruction or preservation, were fully complete (both limbs of the mandible intact, all or most teeth still remaining) and examined them visually, attempting to evaluate their position on a continuum from most-arched to least-arched (in the anterior dental arcade), and most-divergent to least-divergent (in the limbs of the mandible); this process is mostly for initial convenience, and will be corrected (or not) by concrete empirical measurement.
What comes next week, then, is beginning to take the measurements. All of the measurements will be taken digitally to ensure as much accuracy as possible, especially on reconstructions. Therefore, measurement requires photography on a standard mandible orientation. At this point, it looks like we might be using Photoshop and Image J for our purposes in two dimensions -- if we upgrade to three, we will have to use a digitiser.
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