FIGURE 3 in Application of shell spiral deviation methodology to fossil brachiopods: Implications for obtaining specimen ontogenetic ages

FIGURE 3. Example of shell (Laqueus rubellus) digitization and spiral fitting. 1, The brachiopod shell was digitized by clicking the outline in an anterior-ward direction, starting at the umbo. 2, The digitized outline was saved as (x,y) coordinates, which were used to plot a biological outline in R. 3, R code was used to fit a perfect logarithmic spiral to the shell outline. 4, The deviations from a perfect spiral were represented in a spiral deviation graph, with green points representing spiral maxima and red points representing spiral minima.