Bolstering geometric morphometrics sample sizes with damaged and pathologic specimens: Is near enough good enough?

Area of Science:

• Paleontology
• Biological Anthropology
• Comparative Anatomy

Background:

• Geometric morphometric studies often rely on museum skeletal specimens.
• Damaged or pathological specimens are typically excluded from shape analyses.
• Previous research on specimen inclusion has been limited to 2D data.

Purpose of the Study:

• To investigate the impact of including damaged/pathological specimens in 3D geometric morphometric analyses.
• To determine if these specimens strengthen or confound shape variation analyses.
• To assess the utility of damaged specimens for understanding intraspecific shape variation.

Main Methods:

• Collected 3D coordinate data from 100 crab-eating macaque crania and mandibles.
• Analyzed five datasets with varying degrees of specimen damage/pathology.
• Compared results from datasets including questionable specimens with those of high-quality specimens.

Main Results:

• Inclusion of damaged/pathological specimens increased variation linked to allometry, sexual dimorphism, and covariation.
• Analysis of only questionable specimens yielded consistent results for dominant shape aspects but affected minor components.
• Bolstered small datasets with damaged specimens adequately assessed major shape components, revealing finer scale differences.

Conclusions:

• Damaged/pathological specimens contribute normal, repeatable variation, emphasizing dominant shape predictors in larger datasets.
• Exclusion of these specimens may omit important demographic-specific shape variation.
• Inclusion is recommended for studies on dominant intraspecific shape variation, with caution for fine-scale analyses.