Biology Reference
In-Depth Information
and low time investment inherent in the technique. As with other research methods, the time
and money that certain techniques require can greatly affect the types of research questions
that might be explored. Limitations on sample sizes and the time and resources necessary to
collect and analyze comparative samples should also be considered.
Pits and scratches are the two main features usually evaluated in microwear studies. Pits
are somewhat circular indentations in the enamel surface and scratches are more linear
features that are most often defined as having a length to width ratio of 4:1. Some researchers
have used ratios of 2:1 or 10:1 to distinguish the more linear scratch from the “spot” of the pit
(
Ungar et al., 2008
). However arbitrary these definitions may be, they are designed to distin-
guish between two different features that appear to be representative of different types of die-
tary abrasives.
One methodological issue that warrants consideration with both types of microscopy
commonly used in microwear analysis (both SEM and low-level magnification) is the docu-
mentation, both qualitatively and quantitatively, of a three-dimensional surface and associ-
ated features with two-dimensional imaging techniques. That is to say that although we can
recognize different features and count and group them in order to come up with profiles,
we have a difficult time measuring depth of pits and scratches or the surface relief of
a tooth.
In this vein, Ungar and colleagues (2008) have developed an automated method that
tracks “surface complexity” rather than relying on manually collected data. They report
that the method is fully automated, which reduces costs and time, and virtually eliminates
the previously mentioned high rates of interobserver error. By examining measures that
describe overall surface topography, their method records a three-dimensional account of
the appearance of microwear on the tooth surface. Comparing like surfaces, this method
found fewer surface complexities in folivores (leaf eaters) than in other primates. Significant
differences also existed within species, indicating differential exploitation of available dietary
resources.
To place this in a human context, we can consider the things that humans do with their
teeth that might contribute to differences in their microwear patterns. In addition to diet,
use of the teeth as a ”tool” contributes to microwear variation between populations. For
an extensive review on the occupational use of the dentition as a tool and appropriate
recording methodologies, see
Molnar (2011)
.
CASE STUDY: THE DEVIL IS IN THE DETAILS
My area of interest is dental development, and more specifically, how it relates to the
evolution of life history in fossil hominins. As discussed earlier, in this area of research tooth
growth is used to interpret the overall pace of life in our ancestors. To do this, we rely on our
understanding of the complex interconnectedness of the body's systems. My work engages
the interactions of these systems by using the teeth as a proxy for the chronology of important
life history events such as age at weaning, menarche, and first reproduction.
My dissertation topic grew out of my Master's thesis, which studied the prenatal develop-
ment of the teeth in Macaca nemestrina (the pigtailed macaque). I was lucky enough to be in
a programwhere my advisor had an extensive collection of lateral X-rays from a collection of
