Landmark Typology in Applied Morphometrics Studies: What's the Point?

Area of Science:

• Morphological analysis
• Biological shape analysis
• Geometric morphometrics

Background:

• Landmarks are essential for biological shape analysis, serving as discrete anatomical points.
• Bookstein's widely used system classifies landmarks into three types based on anatomical location and biological significance.
• This typology has been used to justify landmark selection or exclusion in analyses due to perceived differences in information content and reliability.

Purpose of the Study:

• To investigate the consistency of landmark classification in geometric morphometrics (GM).
• To evaluate the correlation between landmark type and measurement reproducibility.
• To assess the utility of landmark typology in applied GM research.

Main Methods:

• Reviewed 17 studies employing geometric morphometrics.
• Analyzed variations in landmark classifications based on Bookstein's typology and individual landmark definitions.
• Examined literature for correlations between landmark type and measurement reproducibility, considering measurement tools and data sources.

Main Results:

• Demonstrated considerable variation in landmark classifications among studies, indicating disagreement in applying Bookstein's typology and definitions.
• Found little correlation between landmark type and measurement reproducibility.
• Identified that measurement tools and data sources significantly impact reproducibility, independent of landmark type.

Conclusions:

• Landmark typology, while useful for teaching, introduces confusion in research design and offers little practical information.
• Researchers should prioritize landmark configurations that test specific hypotheses.
• Justification of landmark choices, definitions, collection methods, and reproducibility analyses are crucial for applied GM studies.