Fig. 5: A simplified demonstration of how size can drive covariance between two characters.
From: Environmental drivers of body size evolution in crocodile-line archosaurs
In this two-dimensional example, relative size is indicated by the position of points along the trend line, which corresponds to the first axis returned by principal components analysis. Variations in shape are indicated by position on the orthogonal second component. A positive correlation between traits may be driven by factors other than size, therefore this study uses 21 characters, rather than just two.
