What are morphometrics and archaeological morphometrics?
Morphometrics is the quantitative study and statistical analysis of size and shape. Together these define the form of an object studied. It is a methodological framework which can benefit any research field which depends upon comparative morphology; this includes evolutionary biology, systematics, ecology, physical anthropology, orthodontics etc.
The shape of an object, dataset or image can be defined as “the total of all information that is invariant under translation, rotations and isotropic rescalings” (Small, 1996).
Size refers to the spatial extent of an organism, and can be measured in different methods e.g. area, lengths, widths, sum of widths etc.
Two different styles of morphometrics are recognised, by the nature of data being analysed: traditional and geometric morphometrics.
Archaeological morphometrics is therefore the application of morphometrics within archaeological analyses. This can be applied to a variety of archaeological materials including, but not limited to, lithics, ceramics, skeletal, zooarchaeological and metalwork.
What are “traditional morphometrics”?
Traditional morphometrics involve categorising morphology in terms of lineal measurements (ratios, lengths, angles…) which are investigated, in turn, individually (univariate analyses) or several at a time (bivariate and multivariate analyses). Applications have frequently been concerned with allometry (changes in shape as a function of size) and size correction. Techniques incorporate Principal Component Analysis (PCA), Canonical Variate Analysis (CVA) and Discriminant Function Analysis (DFA), to name a few.
And what are “geometric morphometrics”?
Geometric morphometric methodologies are a powerful suite of techniques which provide an immediate visualisation of shape, and the spatial localisation of shape variation. There are, primarily, two branches of geometric morphometrics:
- Landmark-based geometric morphometrics: summarises shape in terms of landmark configuration (discrete anatomical loci, described by two-/three-dimensional Cartesian co-ordinates);
- Outline-based geometric morphometrics: summarises the shape of open or closed curves, typically without fixed landmarks. Analyses include Fourier (Elliptical Fourier, Fast Fourier etc.) and Eigenshape (and Extended Eigenshape) analyses
These are bridged by methods including (but not limited to) Euclidean Distance Matrix Analysis (EDMA), and semilandmarks/semi-landmark analysis..
For more information see blogposts and the website bibliography.