Biology Reference
In-Depth Information
CHAPTER
12
Geo
metric Morphome
trics
Ashley H. McKeown, Ryan W. Schmidt
INTRODUCTION
Geometric morphometrics is a suite of methods for powerful analysis of shape variation.
Geometric morphometrics provides the tools to capture the geometry of a form, retain those
geometric properties throughout analysis, and visualize shape variation among specimens or
groups. The focus in geometric morphometrics is analyzing and visualizing shape variation
in the absence of size differences among specimens. By using
Cartesian
(
x
,
y
, and
z
) coordi-
nates to record morphological structures, the form of a specimen is captured as a two- or
three-dimensional configuration. The coordinates that define the configuration simulta-
neously contain information about landmark location in multiple planes (anterior
e
posterior
(A-P), superior
e
inferior (S-I), and medial
e
lateral (M-L)). The configuration can be plotted as
a two- or three-dimensional object. When geometric morphometric approaches are used for
analysis, this multidimensional information is utilized.
The most popular geometric morphometric approaches offer efficient scaling methods
enabling the analysis of shape variation independent of size. In studies of morphological
variation, size can be an informative parameter or it can be a confounding factor. For
example, there is size and shape variation in craniofacial morphology across human popula-
tions. When trying to estimate sex, size differences between males and females can be infor-
mative. However, when trying to assess variation in morphology across many populations,
size differences can obscure similarities in shape. Geometric morphometrics provides
methods for working solely with shape variation or for integrating size back into the analysis.
This flexibility makes these approaches highly suitable for research in human skeletal
biology.
Further benefits include graphical depictions of morphological variation that can be
used to explain statistical results. Identifying specific differences in landmark location
between groups can provide more in-depth answers about how the variation is patterned,
which can ultimately lead to better interpretations of variability within an evolutionary
framework.
This chapter provides an overview of geometric morphometrics as it is currently applied
to research in human skeletal biology. It is designed to introduce the topic and associated
resources to the reader. Anyone interested in employing geometric morphometrics in their
